/*
 *  API calls related to general value stack manipulation: resizing the value
 *  stack, pushing and popping values, type checking and reading values,
 *  coercing values, etc.
 *
 *  Also contains internal functions (such as duk_get_tval()), defined
 *  in duk_api_internal.h, with semantics similar to the public API.
 */

/* XXX: repetition of stack pre-checks -> helper or macro or inline */
/* XXX: shared api error strings, and perhaps even throw code for rare cases? */

#include "duk_internal.h"

/*
 *  Forward declarations
 */

DUK_LOCAL_DECL duk_idx_t duk__push_c_function_raw(duk_hthread *thr, duk_c_function func, duk_idx_t nargs, duk_uint_t flags, duk_small_uint_t proto_bidx);

/*
 *  Global state for working around missing variadic macros
 */

#if !defined(DUK_USE_VARIADIC_MACROS)
DUK_EXTERNAL const char *duk_api_global_filename = NULL;
DUK_EXTERNAL duk_int_t duk_api_global_line = 0;
#endif

/*
 *  Misc helpers
 */

DUK_LOCAL const char * const duk__symbol_type_strings[4] = {
	"hidden", "global", "local", "wellknown"
};

#if !defined(DUK_USE_PACKED_TVAL)
DUK_LOCAL const duk_uint_t duk__type_from_tag[] = {
	DUK_TYPE_NUMBER,
	DUK_TYPE_NUMBER,  /* fastint */
	DUK_TYPE_UNDEFINED,
	DUK_TYPE_NULL,
	DUK_TYPE_BOOLEAN,
	DUK_TYPE_POINTER,
	DUK_TYPE_LIGHTFUNC,
	DUK_TYPE_NONE,
	DUK_TYPE_STRING,
	DUK_TYPE_OBJECT,
	DUK_TYPE_BUFFER,
};
DUK_LOCAL const duk_uint_t duk__type_mask_from_tag[] = {
	DUK_TYPE_MASK_NUMBER,
	DUK_TYPE_MASK_NUMBER,  /* fastint */
	DUK_TYPE_MASK_UNDEFINED,
	DUK_TYPE_MASK_NULL,
	DUK_TYPE_MASK_BOOLEAN,
	DUK_TYPE_MASK_POINTER,
	DUK_TYPE_MASK_LIGHTFUNC,
	DUK_TYPE_MASK_NONE,
	DUK_TYPE_MASK_STRING,
	DUK_TYPE_MASK_OBJECT,
	DUK_TYPE_MASK_BUFFER,
};
#endif  /* !DUK_USE_PACKED_TVAL */

/* Assert that there's room for one value. */
#define DUK__ASSERT_SPACE() do { \
		DUK_ASSERT(!(thr->valstack_top >= thr->valstack_end)); \
	} while (0)

/* Check that there's room to push one value. */
#if defined(DUK_USE_VALSTACK_UNSAFE)
/* Faster but value stack overruns are memory unsafe. */
#define DUK__CHECK_SPACE() DUK__ASSERT_SPACE()
#else
#define DUK__CHECK_SPACE() do { \
		if (DUK_UNLIKELY(thr->valstack_top >= thr->valstack_end)) { \
			DUK_ERROR_RANGE_PUSH_BEYOND(thr); \
		} \
	} while (0)
#endif

DUK_LOCAL duk_small_uint_t duk__get_symbol_type(duk_hstring *h) {
	const duk_uint8_t *data;
	duk_size_t len;

	DUK_ASSERT(h != NULL);
	DUK_ASSERT(DUK_HSTRING_HAS_SYMBOL(h));
	DUK_ASSERT(DUK_HSTRING_GET_BYTELEN(h) >= 1);  /* always true, symbol prefix */

	data = (const duk_uint8_t *) DUK_HSTRING_GET_DATA(h);
	len = DUK_HSTRING_GET_BYTELEN(h);
	DUK_ASSERT(len >= 1);

	/* XXX: differentiate between 0x82 and 0xff (hidden vs. internal?)? */

	if (data[0] == 0xffU) {
		return DUK_SYMBOL_TYPE_HIDDEN;
	} else if (data[0] == 0x82U) {
		return DUK_SYMBOL_TYPE_HIDDEN;
	} else if (data[0] == 0x80U) {
		return DUK_SYMBOL_TYPE_GLOBAL;
	} else if (data[len - 1] != 0xffU) {
		return DUK_SYMBOL_TYPE_LOCAL;
	} else {
		return DUK_SYMBOL_TYPE_WELLKNOWN;
	}
}

DUK_LOCAL const char *duk__get_symbol_type_string(duk_hstring *h) {
	duk_small_uint_t idx;
	idx = duk__get_symbol_type(h);
	DUK_ASSERT(idx < sizeof(duk__symbol_type_strings));
	return duk__symbol_type_strings[idx];
}

DUK_LOCAL_DECL duk_heaphdr *duk__get_tagged_heaphdr_raw(duk_hthread *thr, duk_idx_t idx, duk_uint_t tag);

DUK_LOCAL duk_int_t duk__api_coerce_d2i(duk_hthread *thr, duk_idx_t idx, duk_int_t def_value, duk_bool_t require) {
	duk_tval *tv;
	duk_small_int_t c;
	duk_double_t d;

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	/*
	 *  Special cases like NaN and +/- Infinity are handled explicitly
	 *  because a plain C coercion from double to int handles these cases
	 *  in undesirable ways.  For instance, NaN may coerce to INT_MIN
	 *  (not zero), and INT_MAX + 1 may coerce to INT_MIN (not INT_MAX).
	 *
	 *  This double-to-int coercion differs from ToInteger() because it
	 *  has a finite range (ToInteger() allows e.g. +/- Infinity).  It
	 *  also differs from ToInt32() because the INT_MIN/INT_MAX clamping
	 *  depends on the size of the int type on the platform.  In particular,
	 *  on platforms with a 64-bit int type, the full range is allowed.
	 */

#if defined(DUK_USE_FASTINT)
	if (DUK_TVAL_IS_FASTINT(tv)) {
		duk_int64_t t = DUK_TVAL_GET_FASTINT(tv);
#if (DUK_INT_MAX <= 0x7fffffffL)
		/* Clamping only necessary for 32-bit ints. */
		if (t < DUK_INT_MIN) {
			t = DUK_INT_MIN;
		} else if (t > DUK_INT_MAX) {
			t = DUK_INT_MAX;
		}
#endif
		return (duk_int_t) t;
	}
#endif

	if (DUK_TVAL_IS_NUMBER(tv)) {
		d = DUK_TVAL_GET_NUMBER(tv);
		c = (duk_small_int_t) DUK_FPCLASSIFY(d);
		if (c == DUK_FP_NAN) {
			return 0;
		} else if (d < (duk_double_t) DUK_INT_MIN) {
			/* covers -Infinity */
			return DUK_INT_MIN;
		} else if (d > (duk_double_t) DUK_INT_MAX) {
			/* covers +Infinity */
			return DUK_INT_MAX;
		} else {
			/* coerce towards zero */
			return (duk_int_t) d;
		}
	}

	if (require) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "number", DUK_STR_NOT_NUMBER);
		DUK_WO_NORETURN(return 0;);
	}

	return def_value;
}

DUK_LOCAL duk_uint_t duk__api_coerce_d2ui(duk_hthread *thr, duk_idx_t idx, duk_uint_t def_value, duk_bool_t require) {
	duk_tval *tv;
	duk_small_int_t c;
	duk_double_t d;

	/* Same as above but for unsigned int range. */

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

#if defined(DUK_USE_FASTINT)
	if (DUK_TVAL_IS_FASTINT(tv)) {
		duk_int64_t t = DUK_TVAL_GET_FASTINT(tv);
		if (t < 0) {
			t = 0;
		}
#if (DUK_UINT_MAX <= 0xffffffffUL)
		/* Clamping only necessary for 32-bit ints. */
		else if (t > DUK_UINT_MAX) {
			t = DUK_UINT_MAX;
		}
#endif
		return (duk_uint_t) t;
	}
#endif

	if (DUK_TVAL_IS_NUMBER(tv)) {
		d = DUK_TVAL_GET_NUMBER(tv);
		c = (duk_small_int_t) DUK_FPCLASSIFY(d);
		if (c == DUK_FP_NAN) {
			return 0;
		} else if (d < 0.0) {
			/* covers -Infinity */
			return (duk_uint_t) 0;
		} else if (d > (duk_double_t) DUK_UINT_MAX) {
			/* covers +Infinity */
			return (duk_uint_t) DUK_UINT_MAX;
		} else {
			/* coerce towards zero */
			return (duk_uint_t) d;
		}
	}

	if (require) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "number", DUK_STR_NOT_NUMBER);
		DUK_WO_NORETURN(return 0;);
	}

	return def_value;
}

/*
 *  Stack index validation/normalization and getting a stack duk_tval ptr.
 *
 *  These are called by many API entrypoints so the implementations must be
 *  fast and "inlined".
 *
 *  There's some repetition because of this; keep the functions in sync.
 */

DUK_EXTERNAL duk_idx_t duk_normalize_index(duk_hthread *thr, duk_idx_t idx) {
	duk_uidx_t vs_size;
	duk_uidx_t uidx;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	/* Care must be taken to avoid pointer wrapping in the index
	 * validation.  For instance, on a 32-bit platform with 8-byte
	 * duk_tval the index 0x20000000UL would wrap the memory space
	 * once.
	 */

	/* Assume value stack sizes (in elements) fits into duk_idx_t. */
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	vs_size = (duk_uidx_t) (thr->valstack_top - thr->valstack_bottom);
	DUK_ASSERT_DISABLE(vs_size >= 0);  /* unsigned */

	if (idx < 0) {
		uidx = vs_size + (duk_uidx_t) idx;
	} else {
		/* since index non-negative */
		DUK_ASSERT(idx != DUK_INVALID_INDEX);
		uidx = (duk_uidx_t) idx;
	}

	/* DUK_INVALID_INDEX won't be accepted as a valid index. */
	DUK_ASSERT(vs_size + (duk_uidx_t) DUK_INVALID_INDEX >= vs_size);

	if (DUK_LIKELY(uidx < vs_size)) {
		return (duk_idx_t) uidx;
	}
	return DUK_INVALID_INDEX;
}

DUK_EXTERNAL duk_idx_t duk_require_normalize_index(duk_hthread *thr, duk_idx_t idx) {
	duk_uidx_t vs_size;
	duk_uidx_t uidx;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	vs_size = (duk_uidx_t) (thr->valstack_top - thr->valstack_bottom);
	DUK_ASSERT_DISABLE(vs_size >= 0);  /* unsigned */

	if (idx < 0) {
		uidx = vs_size + (duk_uidx_t) idx;
	} else {
		DUK_ASSERT(idx != DUK_INVALID_INDEX);
		uidx = (duk_uidx_t) idx;
	}

	/* DUK_INVALID_INDEX won't be accepted as a valid index. */
	DUK_ASSERT(vs_size + (duk_uidx_t) DUK_INVALID_INDEX >= vs_size);

	if (DUK_LIKELY(uidx < vs_size)) {
		return (duk_idx_t) uidx;
	}
	DUK_ERROR_RANGE_INDEX(thr, idx);
	DUK_WO_NORETURN(return 0;);
}

DUK_INTERNAL duk_tval *duk_get_tval(duk_hthread *thr, duk_idx_t idx) {
	duk_uidx_t vs_size;
	duk_uidx_t uidx;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	vs_size = (duk_uidx_t) (thr->valstack_top - thr->valstack_bottom);
	DUK_ASSERT_DISABLE(vs_size >= 0);  /* unsigned */

	if (idx < 0) {
		uidx = vs_size + (duk_uidx_t) idx;
	} else {
		DUK_ASSERT(idx != DUK_INVALID_INDEX);
		uidx = (duk_uidx_t) idx;
	}

	/* DUK_INVALID_INDEX won't be accepted as a valid index. */
	DUK_ASSERT(vs_size + (duk_uidx_t) DUK_INVALID_INDEX >= vs_size);

	if (DUK_LIKELY(uidx < vs_size)) {
		return thr->valstack_bottom + uidx;
	}
	return NULL;
}

/* Variant of duk_get_tval() which is guaranteed to return a valid duk_tval
 * pointer.  When duk_get_tval() would return NULL, this variant returns a
 * pointer to a duk_tval with tag DUK_TAG_UNUSED.  This allows the call site
 * to avoid an unnecessary NULL check which sometimes leads to better code.
 * The return duk_tval is read only (at least for the UNUSED value).
 */
DUK_LOCAL const duk_tval_unused duk__const_tval_unused = DUK_TVAL_UNUSED_INITIALIZER();

DUK_INTERNAL duk_tval *duk_get_tval_or_unused(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval(thr, idx);
	if (tv != NULL) {
		return tv;
	}
	return (duk_tval *) DUK_LOSE_CONST(&duk__const_tval_unused);
}

DUK_INTERNAL duk_tval *duk_require_tval(duk_hthread *thr, duk_idx_t idx) {
	duk_uidx_t vs_size;
	duk_uidx_t uidx;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	vs_size = (duk_uidx_t) (thr->valstack_top - thr->valstack_bottom);
	DUK_ASSERT_DISABLE(vs_size >= 0);  /* unsigned */

	/* Use unsigned arithmetic to optimize comparison. */
	if (idx < 0) {
		uidx = vs_size + (duk_uidx_t) idx;
	} else {
		DUK_ASSERT(idx != DUK_INVALID_INDEX);
		uidx = (duk_uidx_t) idx;
	}

	/* DUK_INVALID_INDEX won't be accepted as a valid index. */
	DUK_ASSERT(vs_size + (duk_uidx_t) DUK_INVALID_INDEX >= vs_size);

	if (DUK_LIKELY(uidx < vs_size)) {
		return thr->valstack_bottom + uidx;
	}
	DUK_ERROR_RANGE_INDEX(thr, idx);
	DUK_WO_NORETURN(return NULL;);
}

/* Non-critical. */
DUK_EXTERNAL duk_bool_t duk_is_valid_index(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	return (duk_normalize_index(thr, idx) >= 0);
}

/* Non-critical. */
DUK_EXTERNAL void duk_require_valid_index(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	if (DUK_UNLIKELY(duk_normalize_index(thr, idx) < 0)) {
		DUK_ERROR_RANGE_INDEX(thr, idx);
		DUK_WO_NORETURN(return;);
	}
}

/*
 *  Value stack top handling
 */

DUK_EXTERNAL duk_idx_t duk_get_top(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
}

/* Internal helper to get current top but to require a minimum top value
 * (TypeError if not met).
 */
DUK_INTERNAL duk_idx_t duk_get_top_require_min(duk_hthread *thr, duk_idx_t min_top) {
	duk_idx_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	if (DUK_UNLIKELY(ret < min_top)) {
		DUK_ERROR_TYPE_INVALID_ARGS(thr);
		DUK_WO_NORETURN(return 0;);
	}
	return ret;
}

/* Set stack top within currently allocated range, but don't reallocate.
 * This is performance critical especially for call handling, so whenever
 * changing, profile and look at generated code.
 */
DUK_EXTERNAL void duk_set_top(duk_hthread *thr, duk_idx_t idx) {
	duk_uidx_t vs_size;
	duk_uidx_t vs_limit;
	duk_uidx_t uidx;
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_INVALID_INDEX < 0);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_end >= thr->valstack_bottom);
	vs_size = (duk_uidx_t) (thr->valstack_top - thr->valstack_bottom);
	vs_limit = (duk_uidx_t) (thr->valstack_end - thr->valstack_bottom);

	if (idx < 0) {
		/* Negative indices are always within allocated stack but
		 * must not go below zero index.
		 */
		uidx = vs_size + (duk_uidx_t) idx;
	} else {
		/* Positive index can be higher than valstack top but must
		 * not go above allocated stack (equality is OK).
		 */
		uidx = (duk_uidx_t) idx;
	}

	/* DUK_INVALID_INDEX won't be accepted as a valid index. */
	DUK_ASSERT(vs_size + (duk_uidx_t) DUK_INVALID_INDEX >= vs_size);
	DUK_ASSERT(vs_size + (duk_uidx_t) DUK_INVALID_INDEX >= vs_limit);

#if defined(DUK_USE_VALSTACK_UNSAFE)
	DUK_ASSERT(uidx <= vs_limit);
	DUK_UNREF(vs_limit);
#else
	if (DUK_UNLIKELY(uidx > vs_limit)) {
		DUK_ERROR_RANGE_INDEX(thr, idx);
		DUK_WO_NORETURN(return;);
	}
#endif
	DUK_ASSERT(uidx <= vs_limit);

	/* Handle change in value stack top.  Respect value stack
	 * initialization policy: 'undefined' above top.  Note that
	 * DECREF may cause a side effect that reallocates valstack,
	 * so must relookup after DECREF.
	 */

	if (uidx >= vs_size) {
		/* Stack size increases or stays the same. */
#if defined(DUK_USE_ASSERTIONS)
		duk_uidx_t count;

		count = uidx - vs_size;
		while (count != 0) {
			count--;
			tv = thr->valstack_top + count;
			DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(tv));
		}
#endif
		thr->valstack_top = thr->valstack_bottom + uidx;
	} else {
		/* Stack size decreases. */
#if defined(DUK_USE_REFERENCE_COUNTING)
		duk_uidx_t count;
		duk_tval *tv_end;

		count = vs_size - uidx;
		DUK_ASSERT(count > 0);
		tv = thr->valstack_top;
		tv_end = tv - count;
		DUK_ASSERT(tv > tv_end);  /* Because count > 0. */
		do {
			tv--;
			DUK_ASSERT(tv >= thr->valstack_bottom);
			DUK_TVAL_SET_UNDEFINED_UPDREF_NORZ(thr, tv);
		} while (tv != tv_end);
		thr->valstack_top = tv_end;
		DUK_REFZERO_CHECK_FAST(thr);
#else  /* DUK_USE_REFERENCE_COUNTING */
		duk_uidx_t count;
		duk_tval *tv_end;

		count = vs_size - uidx;
		tv = thr->valstack_top;
		tv_end = tv - count;
		DUK_ASSERT(tv > tv_end);
		do {
			tv--;
			DUK_TVAL_SET_UNDEFINED(tv);
		} while (tv != tv_end);
		thr->valstack_top = tv_end;
#endif  /* DUK_USE_REFERENCE_COUNTING */
	}
}

/* Internal variant with a non-negative index and no runtime size checks. */
#if defined(DUK_USE_PREFER_SIZE)
DUK_INTERNAL void duk_set_top_unsafe(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_set_top(thr, idx);
}
#else  /* DUK_USE_PREFER_SIZE */
DUK_INTERNAL void duk_set_top_unsafe(duk_hthread *thr, duk_idx_t idx) {
	duk_uidx_t uidx;
	duk_uidx_t vs_size;
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_end >= thr->valstack_bottom);
	DUK_ASSERT(idx >= 0);
	DUK_ASSERT(idx <= (duk_idx_t) (thr->valstack_end - thr->valstack_bottom));

	/* XXX: byte arithmetic */
	uidx = (duk_uidx_t) idx;
	vs_size = (duk_uidx_t) (thr->valstack_top - thr->valstack_bottom);

	if (uidx >= vs_size) {
		/* Stack size increases or stays the same. */
#if defined(DUK_USE_ASSERTIONS)
		duk_uidx_t count;

		count = uidx - vs_size;
		while (count != 0) {
			count--;
			tv = thr->valstack_top + count;
			DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(tv));
		}
#endif
		thr->valstack_top = thr->valstack_bottom + uidx;
	} else {
		/* Stack size decreases. */
#if defined(DUK_USE_REFERENCE_COUNTING)
		duk_uidx_t count;
		duk_tval *tv_end;

		count = vs_size - uidx;
		DUK_ASSERT(count > 0);
		tv = thr->valstack_top;
		tv_end = tv - count;
		DUK_ASSERT(tv > tv_end);  /* Because count > 0. */
		do {
			tv--;
			DUK_ASSERT(tv >= thr->valstack_bottom);
			DUK_TVAL_SET_UNDEFINED_UPDREF_NORZ(thr, tv);
		} while (tv != tv_end);
		thr->valstack_top = tv_end;
		DUK_REFZERO_CHECK_FAST(thr);
#else  /* DUK_USE_REFERENCE_COUNTING */
		duk_uidx_t count;
		duk_tval *tv_end;

		count = vs_size - uidx;
		tv = thr->valstack_top;
		tv_end = tv - count;
		DUK_ASSERT(tv > tv_end);
		do {
			tv--;
			DUK_TVAL_SET_UNDEFINED(tv);
		} while (tv != tv_end);
		thr->valstack_top = tv_end;
#endif  /* DUK_USE_REFERENCE_COUNTING */
	}
}
#endif  /* DUK_USE_PREFER_SIZE */

/* Internal helper: set top to 'top', and set [idx_wipe_start,top[ to
 * 'undefined' (doing nothing if idx_wipe_start == top).  Indices are
 * positive and within value stack reserve.  This is used by call handling.
 */
DUK_INTERNAL void duk_set_top_and_wipe(duk_hthread *thr, duk_idx_t top, duk_idx_t idx_wipe_start) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(top >= 0);
	DUK_ASSERT(idx_wipe_start >= 0);
	DUK_ASSERT(idx_wipe_start <= top);
	DUK_ASSERT(thr->valstack_bottom + top <= thr->valstack_end);
	DUK_ASSERT(thr->valstack_bottom + idx_wipe_start <= thr->valstack_end);

	duk_set_top_unsafe(thr, idx_wipe_start);
	duk_set_top_unsafe(thr, top);
}

DUK_EXTERNAL duk_idx_t duk_get_top_index(duk_hthread *thr) {
	duk_idx_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom) - 1;
	if (DUK_UNLIKELY(ret < 0)) {
		/* Return invalid index; if caller uses this without checking
		 * in another API call, the index won't map to a valid stack
		 * entry.
		 */
		return DUK_INVALID_INDEX;
	}
	return ret;
}

/* Internal variant: call assumes there is at least one element on the value
 * stack frame; this is only asserted for.
 */
DUK_INTERNAL duk_idx_t duk_get_top_index_unsafe(duk_hthread *thr) {
	duk_idx_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom) - 1;
	return ret;
}

DUK_EXTERNAL duk_idx_t duk_require_top_index(duk_hthread *thr) {
	duk_idx_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom) - 1;
	if (DUK_UNLIKELY(ret < 0)) {
		DUK_ERROR_RANGE_INDEX(thr, -1);
		DUK_WO_NORETURN(return 0;);
	}
	return ret;
}

/*
 *  Value stack resizing.
 *
 *  This resizing happens above the current "top": the value stack can be
 *  grown or shrunk, but the "top" is not affected.  The value stack cannot
 *  be resized to a size below the current reserve.
 *
 *  The low level reallocation primitive must carefully recompute all value
 *  stack pointers, and must also work if ALL pointers are NULL.  The resize
 *  is quite tricky because the valstack realloc may cause a mark-and-sweep,
 *  which may run finalizers.  Running finalizers may resize the valstack
 *  recursively (the same value stack we're working on).  So, after realloc
 *  returns, we know that the valstack bottom, top, and reserve should still
 *  be the same (there should not be live values above the "top"), but its
 *  underlying size, alloc_end, and base pointer may have changed.
 *
 *  'new_size' is known to be <= DUK_USE_VALSTACK_LIMIT, which ensures that
 *  size_t and pointer arithmetic won't wrap in duk__resize_valstack().
 */

/* Low level valstack resize primitive, used for both grow and shrink.  All
 * adjustments for slack etc have already been done.  Doesn't throw but does
 * have allocation side effects.
 */
DUK_LOCAL DUK_COLD DUK_NOINLINE duk_bool_t duk__resize_valstack(duk_hthread *thr, duk_size_t new_size) {
	duk_tval *pre_valstack;
	duk_tval *pre_bottom;
	duk_tval *pre_top;
	duk_tval *pre_end;
	duk_tval *pre_alloc_end;
	duk_ptrdiff_t ptr_diff;
	duk_tval *new_valstack;
	duk_size_t new_alloc_size;
	duk_tval *tv_prev_alloc_end;
	duk_tval *p;

	DUK_HTHREAD_ASSERT_VALID(thr);
	DUK_ASSERT(thr->valstack_bottom >= thr->valstack);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_end >= thr->valstack_top);
	DUK_ASSERT(thr->valstack_alloc_end >= thr->valstack_end);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack) <= new_size);  /* can't resize below 'top' */
	DUK_ASSERT(new_size <= DUK_USE_VALSTACK_LIMIT);  /* valstack limit caller has check, prevents wrapping */
	DUK_ASSERT(new_size <= DUK_SIZE_MAX / sizeof(duk_tval));  /* specific assert for wrapping */

	/* Pre-realloc pointer copies for asserts and debug logs. */
	pre_valstack = thr->valstack;
	pre_bottom = thr->valstack_bottom;
	pre_top = thr->valstack_top;
	pre_end = thr->valstack_end;
	pre_alloc_end = thr->valstack_alloc_end;

	DUK_UNREF(pre_valstack);
	DUK_UNREF(pre_bottom);
	DUK_UNREF(pre_top);
	DUK_UNREF(pre_end);
	DUK_UNREF(pre_alloc_end);

	/* If finalizer torture enabled, force base pointer change every time
	 * when it would be allowed.
	 */
#if defined(DUK_USE_FINALIZER_TORTURE)
	if (thr->heap->pf_prevent_count == 0) {
		duk_hthread_valstack_torture_realloc(thr);
	}
#endif

	/* Allocate a new valstack using DUK_REALLOC_DIRECT() to deal with
	 * a side effect changing the base pointer.
	 */
	new_alloc_size = sizeof(duk_tval) * new_size;
	new_valstack = (duk_tval *) DUK_REALLOC_INDIRECT(thr->heap, duk_hthread_get_valstack_ptr, (void *) thr, new_alloc_size);
	if (DUK_UNLIKELY(new_valstack == NULL)) {
		/* Because new_size != 0, if condition doesn't need to be
		 * (new_valstack != NULL || new_size == 0).
		 */
		DUK_ASSERT(new_size != 0);
		DUK_D(DUK_DPRINT("failed to resize valstack to %lu entries (%lu bytes)",
		                 (unsigned long) new_size, (unsigned long) new_alloc_size));
		return 0;
	}

	/* Debug log any changes in pointer(s) by side effects.  These don't
	 * necessarily imply any incorrect behavior, but should be rare in
	 * practice.
	 */
#if defined(DUK_USE_DEBUG)
	if (thr->valstack != pre_valstack) {
		DUK_D(DUK_DPRINT("valstack base pointer changed during valstack resize: %p -> %p",
		                 (void *) pre_valstack, (void *) thr->valstack));
	}
	if (thr->valstack_bottom != pre_bottom) {
		DUK_D(DUK_DPRINT("valstack bottom pointer changed during valstack resize: %p -> %p",
		                 (void *) pre_bottom, (void *) thr->valstack_bottom));
	}
	if (thr->valstack_top != pre_top) {
		DUK_D(DUK_DPRINT("valstack top pointer changed during valstack resize: %p -> %p",
		                 (void *) pre_top, (void *) thr->valstack_top));
	}
	if (thr->valstack_end != pre_end) {
		DUK_D(DUK_DPRINT("valstack end pointer changed during valstack resize: %p -> %p",
		                 (void *) pre_end, (void *) thr->valstack_end));
	}
	if (thr->valstack_alloc_end != pre_alloc_end) {
		DUK_D(DUK_DPRINT("valstack alloc_end pointer changed during valstack resize: %p -> %p",
		                 (void *) pre_alloc_end, (void *) thr->valstack_alloc_end));
	}
#endif

	/* Assertions: offsets for bottom, top, and end (reserve) must not
	 * have changed even with side effects because they are always
	 * restored in unwind.  For alloc_end there's no guarantee: it may
	 * have grown or shrunk (but remain above 'end').
	 */
	DUK_ASSERT(thr->valstack_bottom - thr->valstack == pre_bottom - pre_valstack);
	DUK_ASSERT(thr->valstack_top - thr->valstack == pre_top - pre_valstack);
	DUK_ASSERT(thr->valstack_end - thr->valstack == pre_end - pre_valstack);
	DUK_ASSERT(thr->valstack_alloc_end >= thr->valstack_end);

	/* Write new pointers.  Most pointers can be handled as a pointer
	 * difference.
	 */
	ptr_diff = (duk_ptrdiff_t) ((duk_uint8_t *) new_valstack - (duk_uint8_t *) thr->valstack);
	tv_prev_alloc_end = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack_alloc_end + ptr_diff);
	thr->valstack = new_valstack;
	thr->valstack_bottom = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack_bottom + ptr_diff);
	thr->valstack_top = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack_top + ptr_diff);
	thr->valstack_end = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack_end + ptr_diff);
	thr->valstack_alloc_end = (duk_tval *) (void *) ((duk_uint8_t *) new_valstack + new_alloc_size);

	/* Assertions: pointer sanity after pointer updates. */
	DUK_ASSERT(thr->valstack_bottom >= thr->valstack);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_end >= thr->valstack_top);
	DUK_ASSERT(thr->valstack_alloc_end >= thr->valstack_end);

	DUK_D(DUK_DPRINT("resized valstack %lu -> %lu elements (%lu -> %lu bytes): "
	                 "base=%p -> %p, bottom=%p -> %p (%ld), top=%p -> %p (%ld), "
	                 "end=%p -> %p (%ld), alloc_end=%p -> %p (%ld);"
	                 " tv_prev_alloc_end=%p (-> %ld inits; <0 means shrink)",
	                 (unsigned long) (pre_alloc_end - pre_valstack),
	                 (unsigned long) new_size,
	                 (unsigned long) ((duk_uint8_t *) pre_alloc_end - (duk_uint8_t *) pre_valstack),
	                 (unsigned long) new_alloc_size,
	                 (void *) pre_valstack, (void *) thr->valstack,
	                 (void *) pre_bottom, (void *) thr->valstack_bottom, (long) (thr->valstack_bottom - thr->valstack),
	                 (void *) pre_top, (void *) thr->valstack_top, (long) (thr->valstack_top - thr->valstack),
	                 (void *) pre_end, (void *) thr->valstack_end, (long) (thr->valstack_end - thr->valstack),
	                 (void *) pre_alloc_end, (void *) thr->valstack_alloc_end, (long) (thr->valstack_alloc_end - thr->valstack),
	                 (void *) tv_prev_alloc_end, (long) (thr->valstack_alloc_end - tv_prev_alloc_end)));

	/* If allocation grew, init any new slots to 'undefined'. */
	p = tv_prev_alloc_end;
	while (p < thr->valstack_alloc_end) {
		/* Never executed if new size is smaller. */
		DUK_TVAL_SET_UNDEFINED(p);
		p++;
	}

	/* Assert for value stack initialization policy. */
#if defined(DUK_USE_ASSERTIONS)
	p = thr->valstack_top;
	while (p < thr->valstack_alloc_end) {
		DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(p));
		p++;
	}
#endif

	return 1;
}

DUK_LOCAL DUK_COLD DUK_NOINLINE duk_bool_t duk__valstack_grow(duk_hthread *thr, duk_size_t min_bytes, duk_bool_t throw_on_error) {
	duk_size_t min_size;
	duk_size_t new_size;

	DUK_ASSERT(min_bytes / sizeof(duk_tval) * sizeof(duk_tval) == min_bytes);
	min_size = min_bytes / sizeof(duk_tval);  /* from bytes to slots */

#if defined(DUK_USE_VALSTACK_GROW_SHIFT)
	/* New size is minimum size plus a proportional slack, e.g. shift of
	 * 2 means a 25% slack.
	 */
	new_size = min_size + (min_size >> DUK_USE_VALSTACK_GROW_SHIFT);
#else
	/* New size is tight with no slack.  This is sometimes preferred in
	 * low memory environments.
	 */
	new_size = min_size;
#endif

	if (DUK_UNLIKELY(new_size > DUK_USE_VALSTACK_LIMIT || new_size < min_size /*wrap*/)) {
		/* Note: may be triggered even if minimal new_size would not reach the limit,
		 * plan limit accordingly.
		 */
		if (throw_on_error) {
			DUK_ERROR_RANGE(thr, DUK_STR_VALSTACK_LIMIT);
			DUK_WO_NORETURN(return 0;);
		}
		return 0;
	}

	if (duk__resize_valstack(thr, new_size) == 0) {
		if (throw_on_error) {
			DUK_ERROR_ALLOC_FAILED(thr);
			DUK_WO_NORETURN(return 0;);
		}
		return 0;
	}

	thr->valstack_end = thr->valstack + min_size;
	DUK_ASSERT(thr->valstack_alloc_end >= thr->valstack_end);

	return 1;
}

/* Hot, inlined value stack grow check.  Because value stack almost never
 * grows, the actual resize call is in a NOINLINE helper.
 */
DUK_INTERNAL DUK_INLINE void duk_valstack_grow_check_throw(duk_hthread *thr, duk_size_t min_bytes) {
	duk_tval *tv;

	tv = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack + min_bytes);
	if (DUK_LIKELY(thr->valstack_end >= tv)) {
		return;
	}
	if (DUK_LIKELY(thr->valstack_alloc_end >= tv)) {
		/* Values in [valstack_top,valstack_alloc_end[ are initialized
		 * to 'undefined' so we can just move the end pointer.
		 */
		thr->valstack_end = tv;
		return;
	}
	(void) duk__valstack_grow(thr, min_bytes, 1 /*throw_on_error*/);
}

/* Hot, inlined value stack grow check which doesn't throw. */
DUK_INTERNAL DUK_INLINE duk_bool_t duk_valstack_grow_check_nothrow(duk_hthread *thr, duk_size_t min_bytes) {
	duk_tval *tv;

	tv = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack + min_bytes);
	if (DUK_LIKELY(thr->valstack_end >= tv)) {
		return 1;
	}
	if (DUK_LIKELY(thr->valstack_alloc_end >= tv)) {
		thr->valstack_end = tv;
		return 1;
	}
	return duk__valstack_grow(thr, min_bytes, 0 /*throw_on_error*/);
}

/* Value stack shrink check, called from mark-and-sweep. */
DUK_INTERNAL void duk_valstack_shrink_check_nothrow(duk_hthread *thr, duk_bool_t snug) {
	duk_size_t alloc_bytes;
	duk_size_t reserve_bytes;
	duk_size_t shrink_bytes;

	alloc_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_alloc_end - (duk_uint8_t *) thr->valstack);
	reserve_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_end - (duk_uint8_t *) thr->valstack);
	DUK_ASSERT(alloc_bytes >= reserve_bytes);

	/* We're free to shrink the value stack allocation down to
	 * reserve_bytes but not more.  If 'snug' (emergency GC)
	 * shrink whatever we can.  Otherwise only shrink if the new
	 * size would be considerably smaller.
	 */

#if defined(DUK_USE_VALSTACK_SHRINK_CHECK_SHIFT)
	if (snug) {
		shrink_bytes = reserve_bytes;
	} else {
		duk_size_t proportion, slack;

		/* Require that value stack shrinks by at least X% of its
		 * current size.  For example, shift of 2 means at least
		 * 25%.  The proportion is computed as bytes and may not
		 * be a multiple of sizeof(duk_tval); that's OK here.
		 */
		proportion = alloc_bytes >> DUK_USE_VALSTACK_SHRINK_CHECK_SHIFT;
		if (alloc_bytes - reserve_bytes < proportion) {
			/* Too little would be freed, do nothing. */
			return;
		}

		/* Keep a slack after shrinking.  The slack is again a
		 * proportion of the current size (the proportion should
		 * of course be smaller than the check proportion above).
		 */
#if defined(DUK_USE_VALSTACK_SHRINK_SLACK_SHIFT)
		DUK_ASSERT(DUK_USE_VALSTACK_SHRINK_SLACK_SHIFT > DUK_USE_VALSTACK_SHRINK_CHECK_SHIFT);
		slack = alloc_bytes >> DUK_USE_VALSTACK_SHRINK_SLACK_SHIFT;
#else
		slack = 0;
#endif
		shrink_bytes = reserve_bytes +
		               slack / sizeof(duk_tval) * sizeof(duk_tval);  /* multiple of duk_tval */
	}
#else  /* DUK_USE_VALSTACK_SHRINK_CHECK_SHIFT */
	/* Always snug, useful in some low memory environments. */
	DUK_UNREF(snug);
	shrink_bytes = reserve_bytes;
#endif  /* DUK_USE_VALSTACK_SHRINK_CHECK_SHIFT */

	DUK_D(DUK_DPRINT("valstack shrink check: alloc_bytes=%ld, reserve_bytes=%ld, shrink_bytes=%ld (unvalidated)",
	                 (long) alloc_bytes, (long) reserve_bytes, (long) shrink_bytes));
	DUK_ASSERT(shrink_bytes >= reserve_bytes);
	if (shrink_bytes >= alloc_bytes) {
		/* Skip if shrink target is same as current one (or higher,
		 * though that shouldn't happen in practice).
		 */
		return;
	}
	DUK_ASSERT(shrink_bytes / sizeof(duk_tval) * sizeof(duk_tval) == shrink_bytes);

	DUK_D(DUK_DPRINT("valstack shrink check: decided to shrink, snug: %ld", (long) snug));

	duk__resize_valstack(thr, shrink_bytes / sizeof(duk_tval));
}

DUK_EXTERNAL duk_bool_t duk_check_stack(duk_hthread *thr, duk_idx_t extra) {
	duk_size_t min_new_bytes;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr != NULL);

	if (DUK_UNLIKELY(extra < 0 || extra > DUK_USE_VALSTACK_LIMIT)) {
		if (extra < 0) {
			/* Clamping to zero makes the API more robust to calling code
			 * calculation errors.
			 */
			extra = 0;
		} else {
			/* Cause grow check to fail without wrapping arithmetic. */
			extra = DUK_USE_VALSTACK_LIMIT;
		}
	}

	min_new_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_top - (duk_uint8_t *) thr->valstack) +
	                sizeof(duk_tval) * ((duk_size_t) extra + DUK_VALSTACK_INTERNAL_EXTRA);
	return duk_valstack_grow_check_nothrow(thr, min_new_bytes);
}

DUK_EXTERNAL void duk_require_stack(duk_hthread *thr, duk_idx_t extra) {
	duk_size_t min_new_bytes;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr != NULL);

	if (DUK_UNLIKELY(extra < 0 || extra > DUK_USE_VALSTACK_LIMIT)) {
		if (extra < 0) {
			/* Clamping to zero makes the API more robust to calling code
			 * calculation errors.
			 */
			extra = 0;
		} else {
			/* Cause grow check to fail without wrapping arithmetic. */
			extra = DUK_USE_VALSTACK_LIMIT;
		}
	}

	min_new_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_top - (duk_uint8_t *) thr->valstack) +
	                sizeof(duk_tval) * ((duk_size_t) extra + DUK_VALSTACK_INTERNAL_EXTRA);
	duk_valstack_grow_check_throw(thr, min_new_bytes);
}

DUK_EXTERNAL duk_bool_t duk_check_stack_top(duk_hthread *thr, duk_idx_t top) {
	duk_size_t min_new_bytes;

	DUK_ASSERT_API_ENTRY(thr);

	if (DUK_UNLIKELY(top < 0 || top > DUK_USE_VALSTACK_LIMIT)) {
		if (top < 0) {
			/* Clamping to zero makes the API more robust to calling code
			 * calculation errors.
			 */
			top = 0;
		} else {
			/* Cause grow check to fail without wrapping arithmetic. */
			top = DUK_USE_VALSTACK_LIMIT;
		}
	}

	DUK_ASSERT(top >= 0);
	min_new_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_bottom - (duk_uint8_t *) thr->valstack) +
	                sizeof(duk_tval) * ((duk_size_t) top + DUK_VALSTACK_INTERNAL_EXTRA);
	return duk_valstack_grow_check_nothrow(thr, min_new_bytes);
}

DUK_EXTERNAL void duk_require_stack_top(duk_hthread *thr, duk_idx_t top) {
	duk_size_t min_new_bytes;

	DUK_ASSERT_API_ENTRY(thr);

	if (DUK_UNLIKELY(top < 0 || top > DUK_USE_VALSTACK_LIMIT)) {
		if (top < 0) {
			/* Clamping to zero makes the API more robust to calling code
			 * calculation errors.
			 */
			top = 0;
		} else {
			/* Cause grow check to fail without wrapping arithmetic. */
			top = DUK_USE_VALSTACK_LIMIT;
		}
	}

	DUK_ASSERT(top >= 0);
	min_new_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_bottom - (duk_uint8_t *) thr->valstack) +
	                sizeof(duk_tval) * ((duk_size_t) top + DUK_VALSTACK_INTERNAL_EXTRA);
	duk_valstack_grow_check_throw(thr, min_new_bytes);
}

/*
 *  Basic stack manipulation: swap, dup, insert, replace, etc
 */

DUK_EXTERNAL void duk_swap(duk_hthread *thr, duk_idx_t idx1, duk_idx_t idx2) {
	duk_tval *tv1;
	duk_tval *tv2;
	duk_tval tv_tmp;

	DUK_ASSERT_API_ENTRY(thr);

	tv1 = duk_require_tval(thr, idx1);
	DUK_ASSERT(tv1 != NULL);
	tv2 = duk_require_tval(thr, idx2);
	DUK_ASSERT(tv2 != NULL);

	/* If tv1==tv2 this is a NOP, no check is needed */
	DUK_TVAL_SET_TVAL(&tv_tmp, tv1);
	DUK_TVAL_SET_TVAL(tv1, tv2);
	DUK_TVAL_SET_TVAL(tv2, &tv_tmp);
}

DUK_EXTERNAL void duk_swap_top(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_swap(thr, idx, -1);
}

DUK_EXTERNAL void duk_dup(duk_hthread *thr, duk_idx_t from_idx) {
	duk_tval *tv_from;
	duk_tval *tv_to;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();

	tv_from = duk_require_tval(thr, from_idx);
	tv_to = thr->valstack_top++;
	DUK_ASSERT(tv_from != NULL);
	DUK_ASSERT(tv_to != NULL);
	DUK_TVAL_SET_TVAL(tv_to, tv_from);
	DUK_TVAL_INCREF(thr, tv_to);  /* no side effects */
}

DUK_EXTERNAL void duk_dup_top(duk_hthread *thr) {
#if defined(DUK_USE_PREFER_SIZE)
	duk_dup(thr, -1);
#else
	duk_tval *tv_from;
	duk_tval *tv_to;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();

	if (DUK_UNLIKELY(thr->valstack_top - thr->valstack_bottom <= 0)) {
		DUK_ERROR_RANGE_INDEX(thr, -1);
		DUK_WO_NORETURN(return;);
	}
	tv_from = thr->valstack_top - 1;
	tv_to = thr->valstack_top++;
	DUK_ASSERT(tv_from != NULL);
	DUK_ASSERT(tv_to != NULL);
	DUK_TVAL_SET_TVAL(tv_to, tv_from);
	DUK_TVAL_INCREF(thr, tv_to);  /* no side effects */
#endif
}

DUK_INTERNAL void duk_dup_0(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_dup(thr, 0);
}
DUK_INTERNAL void duk_dup_1(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_dup(thr, 1);
}
DUK_INTERNAL void duk_dup_2(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_dup(thr, 2);
}
DUK_INTERNAL void duk_dup_m2(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_dup(thr, -2);
}
DUK_INTERNAL void duk_dup_m3(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_dup(thr, -3);
}
DUK_INTERNAL void duk_dup_m4(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_dup(thr, -4);
}

DUK_EXTERNAL void duk_insert(duk_hthread *thr, duk_idx_t to_idx) {
	duk_tval *p;
	duk_tval *q;
	duk_tval tv_tmp;
	duk_size_t nbytes;

	DUK_ASSERT_API_ENTRY(thr);

	p = duk_require_tval(thr, to_idx);
	DUK_ASSERT(p != NULL);
	q = duk_require_tval(thr, -1);
	DUK_ASSERT(q != NULL);

	DUK_ASSERT(q >= p);

	/*              nbytes
	 *           <--------->
	 *    [ ... | p | x | x | q ]
	 * => [ ... | q | p | x | x ]
	 */

	nbytes = (duk_size_t) (((duk_uint8_t *) q) - ((duk_uint8_t *) p));

	DUK_DDD(DUK_DDDPRINT("duk_insert: to_idx=%ld, p=%p, q=%p, nbytes=%lu",
	                     (long) to_idx, (void *) p, (void *) q, (unsigned long) nbytes));

	/* No net refcount changes.  No need to special case nbytes == 0
	 * (p == q).
	 */
	DUK_TVAL_SET_TVAL(&tv_tmp, q);
	duk_memmove((void *) (p + 1), (const void *) p, (size_t) nbytes);
	DUK_TVAL_SET_TVAL(p, &tv_tmp);
}

DUK_INTERNAL void duk_insert_undefined(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(idx >= 0);  /* Doesn't support negative indices. */

	duk_push_undefined(thr);
	duk_insert(thr, idx);
}

DUK_INTERNAL void duk_insert_undefined_n(duk_hthread *thr, duk_idx_t idx, duk_idx_t count) {
	duk_tval *tv, *tv_end;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(idx >= 0);  /* Doesn't support negative indices or count. */
	DUK_ASSERT(count >= 0);

	tv = duk_reserve_gap(thr, idx, count);
	tv_end = tv + count;
	while (tv != tv_end) {
		DUK_TVAL_SET_UNDEFINED(tv);
		tv++;
	}
}

DUK_EXTERNAL void duk_pull(duk_hthread *thr, duk_idx_t from_idx) {
	duk_tval *p;
	duk_tval *q;
	duk_tval tv_tmp;
	duk_size_t nbytes;

	DUK_ASSERT_API_ENTRY(thr);

	/*                         nbytes
	 *                       <--------->
	 *    [ ... | x | x | p | y | y | q ]
	 * => [ ... | x | x | y | y | q | p ]
	 */

	p = duk_require_tval(thr, from_idx);
	DUK_ASSERT(p != NULL);
	q = duk_require_tval(thr, -1);
	DUK_ASSERT(q != NULL);

	DUK_ASSERT(q >= p);

	nbytes = (duk_size_t) (((duk_uint8_t *) q) - ((duk_uint8_t *) p));

	DUK_DDD(DUK_DDDPRINT("duk_pull: from_idx=%ld, p=%p, q=%p, nbytes=%lu",
	                     (long) from_idx, (void *) p, (void *) q, (unsigned long) nbytes));

	/* No net refcount changes.  No need to special case nbytes == 0
	 * (p == q).
	 */
	DUK_TVAL_SET_TVAL(&tv_tmp, p);
	duk_memmove((void *) p, (const void *) (p + 1), (size_t) nbytes);
	DUK_TVAL_SET_TVAL(q, &tv_tmp);
}

DUK_EXTERNAL void duk_replace(duk_hthread *thr, duk_idx_t to_idx) {
	duk_tval *tv1;
	duk_tval *tv2;
	duk_tval tv_tmp;

	DUK_ASSERT_API_ENTRY(thr);

	tv1 = duk_require_tval(thr, -1);
	DUK_ASSERT(tv1 != NULL);
	tv2 = duk_require_tval(thr, to_idx);
	DUK_ASSERT(tv2 != NULL);

	/* For tv1 == tv2, both pointing to stack top, the end result
	 * is same as duk_pop(thr).
	 */
	DUK_TVAL_SET_TVAL(&tv_tmp, tv2);
	DUK_TVAL_SET_TVAL(tv2, tv1);
	DUK_TVAL_SET_UNDEFINED(tv1);
	thr->valstack_top--;
	DUK_TVAL_DECREF(thr, &tv_tmp);  /* side effects */
}

DUK_EXTERNAL void duk_copy(duk_hthread *thr, duk_idx_t from_idx, duk_idx_t to_idx) {
	duk_tval *tv1;
	duk_tval *tv2;

	DUK_ASSERT_API_ENTRY(thr);

	tv1 = duk_require_tval(thr, from_idx);
	DUK_ASSERT(tv1 != NULL);
	tv2 = duk_require_tval(thr, to_idx);
	DUK_ASSERT(tv2 != NULL);

	/* For tv1 == tv2, this is a no-op (no explicit check needed). */
	DUK_TVAL_SET_TVAL_UPDREF(thr, tv2, tv1);  /* side effects */
}

DUK_EXTERNAL void duk_remove(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *p;
	duk_tval *q;
#if defined(DUK_USE_REFERENCE_COUNTING)
	duk_tval tv_tmp;
#endif
	duk_size_t nbytes;

	DUK_ASSERT_API_ENTRY(thr);

	p = duk_require_tval(thr, idx);
	DUK_ASSERT(p != NULL);
	q = duk_require_tval(thr, -1);
	DUK_ASSERT(q != NULL);

	DUK_ASSERT(q >= p);

	/*              nbytes            zero size case
	 *           <--------->
	 *    [ ... | p | x | x | q ]     [ ... | p==q ]
	 * => [ ... | x | x | q ]         [ ... ]
	 */

#if defined(DUK_USE_REFERENCE_COUNTING)
	/* use a temp: decref only when valstack reachable values are correct */
	DUK_TVAL_SET_TVAL(&tv_tmp, p);
#endif

	nbytes = (duk_size_t) (((duk_uint8_t *) q) - ((duk_uint8_t *) p));  /* Note: 'q' is top-1 */
	duk_memmove((void *) p, (const void *) (p + 1), (size_t) nbytes);

	DUK_TVAL_SET_UNDEFINED(q);
	thr->valstack_top--;

#if defined(DUK_USE_REFERENCE_COUNTING)
	DUK_TVAL_DECREF(thr, &tv_tmp);  /* side effects */
#endif
}

DUK_INTERNAL void duk_remove_unsafe(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_remove(thr, idx);  /* XXX: no optimization for now */
}

DUK_INTERNAL void duk_remove_m2(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_remove(thr, -2);
}

DUK_INTERNAL void duk_remove_n(duk_hthread *thr, duk_idx_t idx, duk_idx_t count) {
#if defined(DUK_USE_PREFER_SIZE)
	/* XXX: maybe too slow even when preferring size? */
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(count >= 0);
	DUK_ASSERT(idx >= 0);

	while (count-- > 0) {
		duk_remove(thr, idx);
	}
#else  /* DUK_USE_PREFER_SIZE */
	duk_tval *tv_src;
	duk_tval *tv_dst;
	duk_tval *tv_newtop;
	duk_tval *tv;
	duk_size_t bytes;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(count >= 0);
	DUK_ASSERT(idx >= 0);

	tv_dst = thr->valstack_bottom + idx;
	DUK_ASSERT(tv_dst <= thr->valstack_top);
	tv_src = tv_dst + count;
	DUK_ASSERT(tv_src <= thr->valstack_top);
	bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_top - (duk_uint8_t *) tv_src);

	for (tv = tv_dst; tv < tv_src; tv++) {
		DUK_TVAL_DECREF_NORZ(thr, tv);
	}

	duk_memmove((void *) tv_dst, (const void *) tv_src, bytes);

	tv_newtop = thr->valstack_top - count;
	for (tv = tv_newtop; tv < thr->valstack_top; tv++) {
		DUK_TVAL_SET_UNDEFINED(tv);
	}
	thr->valstack_top = tv_newtop;

	/* When not preferring size, only NORZ macros are used; caller
	 * is expected to DUK_REFZERO_CHECK().
	 */
#endif  /* DUK_USE_PREFER_SIZE */
}

DUK_INTERNAL void duk_remove_n_unsafe(duk_hthread *thr, duk_idx_t idx, duk_idx_t count) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_remove_n(thr, idx, count);  /* XXX: no optimization for now */
}

/*
 *  Stack slice primitives
 */

DUK_EXTERNAL void duk_xcopymove_raw(duk_hthread *to_thr, duk_hthread *from_thr, duk_idx_t count, duk_bool_t is_copy) {
	void *src;
	duk_size_t nbytes;
	duk_tval *p;
	duk_tval *q;

	/* XXX: several pointer comparison issues here */

	DUK_ASSERT_API_ENTRY(to_thr);
	DUK_CTX_ASSERT_VALID(to_thr);
	DUK_CTX_ASSERT_VALID(from_thr);
	DUK_ASSERT(to_thr->heap == from_thr->heap);

	if (DUK_UNLIKELY(to_thr == from_thr)) {
		DUK_ERROR_TYPE(to_thr, DUK_STR_INVALID_CONTEXT);
		DUK_WO_NORETURN(return;);
	}
	if (DUK_UNLIKELY((duk_uidx_t) count > (duk_uidx_t) DUK_USE_VALSTACK_LIMIT)) {
		/* Maximum value check ensures 'nbytes' won't wrap below.
		 * Also handles negative count.
		 */
		DUK_ERROR_RANGE_INVALID_COUNT(to_thr);
		DUK_WO_NORETURN(return;);
	}
	DUK_ASSERT(count >= 0);

	nbytes = sizeof(duk_tval) * (duk_size_t) count;
	if (DUK_UNLIKELY(nbytes == 0)) {
		return;
	}
	DUK_ASSERT(to_thr->valstack_top <= to_thr->valstack_end);
	if (DUK_UNLIKELY((duk_size_t) ((duk_uint8_t *) to_thr->valstack_end - (duk_uint8_t *) to_thr->valstack_top) < nbytes)) {
		DUK_ERROR_RANGE_PUSH_BEYOND(to_thr);
		DUK_WO_NORETURN(return;);
	}
	src = (void *) ((duk_uint8_t *) from_thr->valstack_top - nbytes);
	if (DUK_UNLIKELY(src < (void *) from_thr->valstack_bottom)) {
		DUK_ERROR_RANGE_INVALID_COUNT(to_thr);
		DUK_WO_NORETURN(return;);
	}

	/* Copy values (no overlap even if to_thr == from_thr; that's not
	 * allowed now anyway).
	 */
	DUK_ASSERT(nbytes > 0);
	duk_memcpy((void *) to_thr->valstack_top, (const void *) src, (size_t) nbytes);

	p = to_thr->valstack_top;
	to_thr->valstack_top = (duk_tval *) (void *) (((duk_uint8_t *) p) + nbytes);

	if (is_copy) {
		/* Incref copies, keep originals. */
		q = to_thr->valstack_top;
		while (p < q) {
			DUK_TVAL_INCREF(to_thr, p);  /* no side effects */
			p++;
		}
	} else {
		/* No net refcount change. */
		p = from_thr->valstack_top;
		q = (duk_tval *) (void *) (((duk_uint8_t *) p) - nbytes);
		from_thr->valstack_top = q;

		while (p > q) {
			p--;
			DUK_TVAL_SET_UNDEFINED(p);
			/* XXX: fast primitive to set a bunch of values to UNDEFINED */
		}
	}
}

/* Internal helper: reserve a gap of 'count' elements at 'idx_base' and return a
 * pointer to the gap.  Values in the gap are garbage and MUST be initialized by
 * the caller before any side effects may occur.  The caller must ensure there's
 * enough stack reserve for 'count' values.
 */
DUK_INTERNAL duk_tval *duk_reserve_gap(duk_hthread *thr, duk_idx_t idx_base, duk_idx_t count) {
	duk_tval *tv_src;
	duk_tval *tv_dst;
	duk_size_t gap_bytes;
	duk_size_t copy_bytes;

	/* Caller is responsible for ensuring there's enough preallocated
	 * value stack.
	 */
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(count >= 0);
	DUK_ASSERT((duk_size_t) (thr->valstack_end - thr->valstack_top) >= (duk_size_t) count);

	tv_src = thr->valstack_bottom + idx_base;
	gap_bytes = (duk_size_t) count * sizeof(duk_tval);
	tv_dst = (duk_tval *) (void *) ((duk_uint8_t *) tv_src + gap_bytes);
	copy_bytes = (duk_size_t) ((duk_uint8_t *) thr->valstack_top - (duk_uint8_t *) tv_src);
	thr->valstack_top = (duk_tval *) (void *) ((duk_uint8_t *) thr->valstack_top + gap_bytes);
	duk_memmove((void *) tv_dst, (const void *) tv_src, copy_bytes);

	/* Values in the gap are left as garbage: caller must fill them in
	 * and INCREF them before any side effects.
	 */
	return tv_src;
}

/*
 *  Get/opt/require
 */

DUK_EXTERNAL void duk_require_undefined(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_UNDEFINED(tv))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "undefined", DUK_STR_NOT_UNDEFINED);
		DUK_WO_NORETURN(return;);
	}
}

DUK_EXTERNAL void duk_require_null(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_NULL(tv))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "null", DUK_STR_NOT_NULL);
		DUK_WO_NORETURN(return;);
	}
}

DUK_LOCAL DUK_ALWAYS_INLINE duk_bool_t duk__get_boolean_raw(duk_hthread *thr, duk_idx_t idx, duk_bool_t def_value) {
	duk_bool_t ret;
	duk_tval *tv;

	DUK_CTX_ASSERT_VALID(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_TVAL_IS_BOOLEAN(tv)) {
		ret = DUK_TVAL_GET_BOOLEAN(tv);
		DUK_ASSERT(ret == 0 || ret == 1);
	} else {
		ret = def_value;
		/* Not guaranteed to be 0 or 1. */
	}

	return ret;
}

DUK_EXTERNAL duk_bool_t duk_get_boolean(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk__get_boolean_raw(thr, idx, 0);  /* default: false */
}

DUK_EXTERNAL duk_bool_t duk_get_boolean_default(duk_hthread *thr, duk_idx_t idx, duk_bool_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk__get_boolean_raw(thr, idx, def_value);
}

DUK_EXTERNAL duk_bool_t duk_require_boolean(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_bool_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_LIKELY(DUK_TVAL_IS_BOOLEAN(tv))) {
		ret = DUK_TVAL_GET_BOOLEAN(tv);
		DUK_ASSERT(ret == 0 || ret == 1);
		return ret;
	} else {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "boolean", DUK_STR_NOT_BOOLEAN);
		DUK_WO_NORETURN(return 0;);
	}
}

DUK_EXTERNAL duk_bool_t duk_opt_boolean(duk_hthread *thr, duk_idx_t idx, duk_bool_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_boolean(thr, idx);
}

DUK_LOCAL DUK_ALWAYS_INLINE duk_double_t duk__get_number_raw(duk_hthread *thr, duk_idx_t idx, duk_double_t def_value) {
	duk_double_union ret;
	duk_tval *tv;

	DUK_CTX_ASSERT_VALID(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
#if defined(DUK_USE_FASTINT)
	if (DUK_TVAL_IS_FASTINT(tv)) {
		ret.d = (duk_double_t) DUK_TVAL_GET_FASTINT(tv);  /* XXX: cast trick */
	}
	else
#endif
	if (DUK_TVAL_IS_DOUBLE(tv)) {
		/* When using packed duk_tval, number must be in NaN-normalized form
		 * for it to be a duk_tval, so no need to normalize.  NOP for unpacked
		 * duk_tval.
		 */
		ret.d = DUK_TVAL_GET_DOUBLE(tv);
		DUK_ASSERT(DUK_DBLUNION_IS_NORMALIZED(&ret));
	} else {
		ret.d = def_value;
		/* Default value (including NaN) may not be normalized. */
	}

	return ret.d;
}

DUK_EXTERNAL duk_double_t duk_get_number(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_number_raw(thr, idx, DUK_DOUBLE_NAN);  /* default: NaN */
}

DUK_EXTERNAL duk_double_t duk_get_number_default(duk_hthread *thr, duk_idx_t idx, duk_double_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_number_raw(thr, idx, def_value);
}

DUK_EXTERNAL duk_double_t duk_require_number(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_double_union ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_NUMBER(tv))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "number", DUK_STR_NOT_NUMBER);
		DUK_WO_NORETURN(return 0.0;);
	}

	ret.d = DUK_TVAL_GET_NUMBER(tv);

	/* When using packed duk_tval, number must be in NaN-normalized form
	 * for it to be a duk_tval, so no need to normalize.  NOP for unpacked
	 * duk_tval.
	 */
	DUK_ASSERT(DUK_DBLUNION_IS_NORMALIZED(&ret));
	return ret.d;
}

DUK_EXTERNAL duk_double_t duk_opt_number(duk_hthread *thr, duk_idx_t idx, duk_double_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		/* User provided default is not NaN normalized. */
		return def_value;
	}
	return duk_require_number(thr, idx);
}

DUK_EXTERNAL duk_int_t duk_get_int(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_int_t) duk__api_coerce_d2i(thr, idx, 0 /*def_value*/, 0 /*require*/);
}

DUK_EXTERNAL duk_uint_t duk_get_uint(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_uint_t) duk__api_coerce_d2ui(thr, idx, 0 /*def_value*/, 0 /*require*/);
}

DUK_EXTERNAL duk_int_t duk_get_int_default(duk_hthread *thr, duk_idx_t idx, duk_int_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_int_t) duk__api_coerce_d2i(thr, idx, def_value, 0 /*require*/);
}

DUK_EXTERNAL duk_uint_t duk_get_uint_default(duk_hthread *thr, duk_idx_t idx, duk_uint_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_uint_t) duk__api_coerce_d2ui(thr, idx, def_value, 0 /*require*/);
}

DUK_EXTERNAL duk_int_t duk_require_int(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_int_t) duk__api_coerce_d2i(thr, idx, 0 /*def_value*/, 1 /*require*/);
}

DUK_EXTERNAL duk_uint_t duk_require_uint(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_uint_t) duk__api_coerce_d2ui(thr, idx, 0 /*def_value*/, 1 /*require*/);
}

DUK_EXTERNAL duk_int_t duk_opt_int(duk_hthread *thr, duk_idx_t idx, duk_int_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_int(thr, idx);
}

DUK_EXTERNAL duk_uint_t duk_opt_uint(duk_hthread *thr, duk_idx_t idx, duk_uint_t def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_uint(thr, idx);
}

DUK_EXTERNAL const char *duk_get_lstring(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len) {
	duk_hstring *h;
	const char *ret;
	duk_size_t len;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_get_hstring(thr, idx);
	if (h != NULL) {
		len = DUK_HSTRING_GET_BYTELEN(h);
		ret = (const char *) DUK_HSTRING_GET_DATA(h);
	} else {
		len = 0;
		ret = NULL;
	}

	if (out_len != NULL) {
		*out_len = len;
	}
	return ret;
}

DUK_EXTERNAL const char *duk_require_lstring(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_require_hstring(thr, idx);
	DUK_ASSERT(h != NULL);
	if (out_len) {
		*out_len = DUK_HSTRING_GET_BYTELEN(h);
	}
	return (const char *) DUK_HSTRING_GET_DATA(h);
}

DUK_INTERNAL const char *duk_require_lstring_notsymbol(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_require_hstring_notsymbol(thr, idx);
	DUK_ASSERT(h != NULL);
	if (out_len) {
		*out_len = DUK_HSTRING_GET_BYTELEN(h);
	}
	return (const char *) DUK_HSTRING_GET_DATA(h);
}

DUK_EXTERNAL const char *duk_get_string(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_get_hstring(thr, idx);
	if (h != NULL) {
		return (const char *) DUK_HSTRING_GET_DATA(h);
	} else {
		return NULL;
	}
}

DUK_EXTERNAL const char *duk_opt_lstring(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len, const char *def_ptr, duk_size_t def_len) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		if (out_len != NULL) {
			*out_len = def_len;
		}
		return def_ptr;
	}
	return duk_require_lstring(thr, idx, out_len);
}

DUK_EXTERNAL const char *duk_opt_string(duk_hthread *thr, duk_idx_t idx, const char *def_ptr) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_ptr;
	}
	return duk_require_string(thr, idx);
}

DUK_EXTERNAL const char *duk_get_lstring_default(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len, const char *def_ptr, duk_size_t def_len) {
	duk_hstring *h;
	const char *ret;
	duk_size_t len;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_get_hstring(thr, idx);
	if (h != NULL) {
		len = DUK_HSTRING_GET_BYTELEN(h);
		ret = (const char *) DUK_HSTRING_GET_DATA(h);
	} else {
		len = def_len;
		ret = def_ptr;
	}

	if (out_len != NULL) {
		*out_len = len;
	}
	return ret;
}

DUK_EXTERNAL const char *duk_get_string_default(duk_hthread *thr, duk_idx_t idx, const char *def_value) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_get_hstring(thr, idx);
	if (h != NULL) {
		return (const char *) DUK_HSTRING_GET_DATA(h);
	} else {
		return def_value;
	}
}

DUK_INTERNAL const char *duk_get_string_notsymbol(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_get_hstring_notsymbol(thr, idx);
	if (h) {
		return (const char *) DUK_HSTRING_GET_DATA(h);
	} else {
		return NULL;
	}
}

DUK_EXTERNAL const char *duk_require_string(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk_require_lstring(thr, idx, NULL);
}

DUK_INTERNAL const char *duk_require_string_notsymbol(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_require_hstring_notsymbol(thr, idx);
	DUK_ASSERT(h != NULL);
	return (const char *) DUK_HSTRING_GET_DATA(h);
}

DUK_EXTERNAL void duk_require_object(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_OBJECT(tv))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "object", DUK_STR_NOT_OBJECT);
		DUK_WO_NORETURN(return;);
	}
}

DUK_LOCAL void *duk__get_pointer_raw(duk_hthread *thr, duk_idx_t idx, void *def_value) {
	duk_tval *tv;
	void *p;

	DUK_CTX_ASSERT_VALID(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (!DUK_TVAL_IS_POINTER(tv)) {
		return def_value;
	}

	p = DUK_TVAL_GET_POINTER(tv);  /* may be NULL */
	return p;
}

DUK_EXTERNAL void *duk_get_pointer(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_pointer_raw(thr, idx, NULL /*def_value*/);
}

DUK_EXTERNAL void *duk_opt_pointer(duk_hthread *thr, duk_idx_t idx, void *def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_pointer(thr, idx);
}

DUK_EXTERNAL void *duk_get_pointer_default(duk_hthread *thr, duk_idx_t idx, void *def_value) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_pointer_raw(thr, idx, def_value);
}

DUK_EXTERNAL void *duk_require_pointer(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	void *p;

	DUK_ASSERT_API_ENTRY(thr);

	/* Note: here we must be wary of the fact that a pointer may be
	 * valid and be a NULL.
	 */
	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_POINTER(tv))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "pointer", DUK_STR_NOT_POINTER);
		DUK_WO_NORETURN(return NULL;);
	}
	p = DUK_TVAL_GET_POINTER(tv);  /* may be NULL */
	return p;
}

#if 0  /*unused*/
DUK_INTERNAL void *duk_get_voidptr(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_heaphdr *h;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (!DUK_TVAL_IS_HEAP_ALLOCATED(tv)) {
		return NULL;
	}

	h = DUK_TVAL_GET_HEAPHDR(tv);
	DUK_ASSERT(h != NULL);
	return (void *) h;
}
#endif

DUK_LOCAL void *duk__get_buffer_helper(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, void *def_ptr, duk_size_t def_size, duk_bool_t throw_flag) {
	duk_hbuffer *h;
	void *ret;
	duk_size_t len;
	duk_tval *tv;

	DUK_CTX_ASSERT_VALID(thr);

	if (out_size != NULL) {
		*out_size = 0;
	}

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_LIKELY(DUK_TVAL_IS_BUFFER(tv))) {
		h = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h != NULL);

		len = DUK_HBUFFER_GET_SIZE(h);
		ret = DUK_HBUFFER_GET_DATA_PTR(thr->heap, h);
	} else {
		if (throw_flag) {
			DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "buffer", DUK_STR_NOT_BUFFER);
			DUK_WO_NORETURN(return NULL;);
		}
		len = def_size;
		ret = def_ptr;
	}

	if (out_size != NULL) {
		*out_size = len;
	}
	return ret;
}

DUK_EXTERNAL void *duk_get_buffer(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk__get_buffer_helper(thr, idx, out_size, NULL /*def_ptr*/, 0 /*def_size*/, 0 /*throw_flag*/);
}

DUK_EXTERNAL void *duk_opt_buffer(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, void *def_ptr, duk_size_t def_size) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		if (out_size != NULL) {
			*out_size = def_size;
		}
		return def_ptr;
	}
	return duk_require_buffer(thr, idx, out_size);
}

DUK_EXTERNAL void *duk_get_buffer_default(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, void *def_ptr, duk_size_t def_len) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk__get_buffer_helper(thr, idx, out_size, def_ptr, def_len, 0 /*throw_flag*/);
}

DUK_EXTERNAL void *duk_require_buffer(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk__get_buffer_helper(thr, idx, out_size, NULL /*def_ptr*/, 0 /*def_size*/, 1 /*throw_flag*/);
}

/* Get the active buffer data area for a plain buffer or a buffer object.
 * Return NULL if the the value is not a buffer.  Note that a buffer may
 * have a NULL data pointer when its size is zero, the optional 'out_isbuffer'
 * argument allows caller to detect this reliably.
 */
DUK_INTERNAL void *duk_get_buffer_data_raw(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, void *def_ptr, duk_size_t def_size, duk_bool_t throw_flag, duk_bool_t *out_isbuffer) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	if (out_isbuffer != NULL) {
		*out_isbuffer = 0;
	}
	if (out_size != NULL) {
		*out_size = def_size;
	}

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	if (DUK_TVAL_IS_BUFFER(tv)) {
		duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h != NULL);
		if (out_size != NULL) {
			*out_size = DUK_HBUFFER_GET_SIZE(h);
		}
		if (out_isbuffer != NULL) {
			*out_isbuffer = 1;
		}
		return (void *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h);  /* may be NULL (but only if size is 0) */
	}
#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
	else if (DUK_TVAL_IS_OBJECT(tv)) {
		duk_hobject *h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		if (DUK_HOBJECT_IS_BUFOBJ(h)) {
			/* XXX: this is probably a useful shared helper: for a
			 * duk_hbufobj, get a validated buffer pointer/length.
			 */
			duk_hbufobj *h_bufobj = (duk_hbufobj *) h;
			DUK_HBUFOBJ_ASSERT_VALID(h_bufobj);

			if (h_bufobj->buf != NULL &&
			    DUK_HBUFOBJ_VALID_SLICE(h_bufobj)) {
				duk_uint8_t *p;

				p = (duk_uint8_t *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h_bufobj->buf);
				if (out_size != NULL) {
					*out_size = (duk_size_t) h_bufobj->length;
				}
				if (out_isbuffer != NULL) {
					*out_isbuffer = 1;
				}
				return (void *) (p + h_bufobj->offset);
			}
			/* if slice not fully valid, treat as error */
		}
	}
#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */

	if (throw_flag) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "buffer", DUK_STR_NOT_BUFFER);
		DUK_WO_NORETURN(return NULL;);
	}
	return def_ptr;
}

DUK_EXTERNAL void *duk_get_buffer_data(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_get_buffer_data_raw(thr, idx, out_size, NULL /*def_ptr*/, 0 /*def_size*/, 0 /*throw_flag*/, NULL);
}

DUK_EXTERNAL void *duk_get_buffer_data_default(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, void *def_ptr, duk_size_t def_size) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_get_buffer_data_raw(thr, idx, out_size, def_ptr, def_size, 0 /*throw_flag*/, NULL);
}

DUK_EXTERNAL void *duk_opt_buffer_data(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, void *def_ptr, duk_size_t def_size) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		if (out_size != NULL) {
			*out_size = def_size;
		}
		return def_ptr;
	}
	return duk_require_buffer_data(thr, idx, out_size);
}

DUK_EXTERNAL void *duk_require_buffer_data(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_get_buffer_data_raw(thr, idx, out_size, NULL /*def_ptr*/, 0 /*def_size*/, 1 /*throw_flag*/, NULL);
}

/* Raw helper for getting a value from the stack, checking its tag.
 * The tag cannot be a number because numbers don't have an internal
 * tag in the packed representation.
 */

DUK_LOCAL duk_heaphdr *duk__get_tagged_heaphdr_raw(duk_hthread *thr, duk_idx_t idx, duk_uint_t tag) {
	duk_tval *tv;
	duk_heaphdr *ret;

	DUK_CTX_ASSERT_VALID(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_TVAL_GET_TAG(tv) != tag) {
		return (duk_heaphdr *) NULL;
	}

	ret = DUK_TVAL_GET_HEAPHDR(tv);
	DUK_ASSERT(ret != NULL);  /* tagged null pointers should never occur */
	return ret;

}

DUK_INTERNAL duk_hstring *duk_get_hstring(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return (duk_hstring *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_STRING);
}

DUK_INTERNAL duk_hstring *duk_get_hstring_notsymbol(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hstring *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_STRING);
	if (DUK_UNLIKELY(h && DUK_HSTRING_HAS_SYMBOL(h))) {
		return NULL;
	}
	return h;
}

DUK_INTERNAL duk_hstring *duk_require_hstring(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hstring *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_STRING);
	if (DUK_UNLIKELY(h == NULL)) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "string", DUK_STR_NOT_STRING);
		DUK_WO_NORETURN(return NULL;);
	}
	return h;
}

DUK_INTERNAL duk_hstring *duk_require_hstring_notsymbol(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hstring *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_STRING);
	if (DUK_UNLIKELY(h == NULL || DUK_HSTRING_HAS_SYMBOL(h))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "string", DUK_STR_NOT_STRING);
		DUK_WO_NORETURN(return NULL;);
	}
	return h;
}

DUK_INTERNAL duk_hobject *duk_get_hobject(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
}

DUK_INTERNAL duk_hobject *duk_require_hobject(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(h == NULL)) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "object", DUK_STR_NOT_OBJECT);
		DUK_WO_NORETURN(return NULL;);
	}
	return h;
}

DUK_INTERNAL duk_hbuffer *duk_get_hbuffer(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return (duk_hbuffer *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_BUFFER);
}

DUK_INTERNAL duk_hbuffer *duk_require_hbuffer(duk_hthread *thr, duk_idx_t idx) {
	duk_hbuffer *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hbuffer *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_BUFFER);
	if (DUK_UNLIKELY(h == NULL)) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "buffer", DUK_STR_NOT_BUFFER);
		DUK_WO_NORETURN(return NULL;);
	}
	return h;
}

DUK_INTERNAL duk_hthread *duk_get_hthread(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(h != NULL && !DUK_HOBJECT_IS_THREAD(h))) {
		h = NULL;
	}
	return (duk_hthread *) h;
}

DUK_INTERNAL duk_hthread *duk_require_hthread(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(!(h != NULL && DUK_HOBJECT_IS_THREAD(h)))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "thread", DUK_STR_NOT_THREAD);
		DUK_WO_NORETURN(return NULL;);
	}
	return (duk_hthread *) h;
}

DUK_INTERNAL duk_hcompfunc *duk_get_hcompfunc(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(h != NULL && !DUK_HOBJECT_IS_COMPFUNC(h))) {
		h = NULL;
	}
	return (duk_hcompfunc *) h;
}

DUK_INTERNAL duk_hcompfunc *duk_require_hcompfunc(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(!(h != NULL && DUK_HOBJECT_IS_COMPFUNC(h)))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "compiledfunction", DUK_STR_NOT_COMPFUNC);
		DUK_WO_NORETURN(return NULL;);
	}
	return (duk_hcompfunc *) h;
}

DUK_INTERNAL duk_hnatfunc *duk_get_hnatfunc(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(h != NULL && !DUK_HOBJECT_IS_NATFUNC(h))) {
		h = NULL;
	}
	return (duk_hnatfunc *) h;
}

DUK_INTERNAL duk_hnatfunc *duk_require_hnatfunc(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(!(h != NULL && DUK_HOBJECT_IS_NATFUNC(h)))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "nativefunction", DUK_STR_NOT_NATFUNC);
		DUK_WO_NORETURN(return NULL;);
	}
	return (duk_hnatfunc *) h;
}

DUK_EXTERNAL duk_c_function duk_get_c_function(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_hobject *h;
	duk_hnatfunc *f;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_OBJECT(tv))) {
		return NULL;
	}
	h = DUK_TVAL_GET_OBJECT(tv);
	DUK_ASSERT(h != NULL);

	if (DUK_UNLIKELY(!DUK_HOBJECT_IS_NATFUNC(h))) {
		return NULL;
	}
	DUK_ASSERT(DUK_HOBJECT_HAS_NATFUNC(h));
	f = (duk_hnatfunc *) h;

	return f->func;
}

DUK_EXTERNAL duk_c_function duk_opt_c_function(duk_hthread *thr, duk_idx_t idx, duk_c_function def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_c_function(thr, idx);
}

DUK_EXTERNAL duk_c_function duk_get_c_function_default(duk_hthread *thr, duk_idx_t idx, duk_c_function def_value) {
	duk_c_function ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = duk_get_c_function(thr, idx);
	if (ret != NULL) {
		return ret;
	}

	return def_value;
}

DUK_EXTERNAL duk_c_function duk_require_c_function(duk_hthread *thr, duk_idx_t idx) {
	duk_c_function ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = duk_get_c_function(thr, idx);
	if (DUK_UNLIKELY(!ret)) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "nativefunction", DUK_STR_NOT_NATFUNC);
		DUK_WO_NORETURN(return ret;);
	}
	return ret;
}

DUK_EXTERNAL void duk_require_function(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	if (DUK_UNLIKELY(!duk_is_function(thr, idx))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "function", DUK_STR_NOT_FUNCTION);
		DUK_WO_NORETURN(return;);
	}
}

DUK_EXTERNAL void duk_require_constructable(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_require_hobject_accept_mask(thr, idx, DUK_TYPE_MASK_LIGHTFUNC);
	if (DUK_UNLIKELY(h != NULL && !DUK_HOBJECT_HAS_CONSTRUCTABLE(h))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "constructable", DUK_STR_NOT_CONSTRUCTABLE);
		DUK_WO_NORETURN(return;);
	}
	/* Lightfuncs (h == NULL) are constructable. */
}

DUK_EXTERNAL duk_hthread *duk_get_context(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk_get_hthread(thr, idx);
}

DUK_EXTERNAL duk_hthread *duk_require_context(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk_require_hthread(thr, idx);
}

DUK_EXTERNAL duk_hthread *duk_opt_context(duk_hthread *thr, duk_idx_t idx, duk_hthread *def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_context(thr, idx);
}

DUK_EXTERNAL duk_hthread *duk_get_context_default(duk_hthread *thr, duk_idx_t idx, duk_hthread *def_value) {
	duk_hthread *ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = duk_get_context(thr, idx);
	if (ret != NULL) {
		return ret;
	}

	return def_value;
}

DUK_EXTERNAL void *duk_get_heapptr(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	void *ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_HEAP_ALLOCATED(tv))) {
		return (void *) NULL;
	}

	ret = (void *) DUK_TVAL_GET_HEAPHDR(tv);
	DUK_ASSERT(ret != NULL);
	return ret;
}

DUK_EXTERNAL void *duk_opt_heapptr(duk_hthread *thr, duk_idx_t idx, void *def_value) {
	DUK_ASSERT_API_ENTRY(thr);

	if (duk_check_type_mask(thr, idx, DUK_TYPE_MASK_NONE | DUK_TYPE_MASK_UNDEFINED)) {
		return def_value;
	}
	return duk_require_heapptr(thr, idx);
}

DUK_EXTERNAL void *duk_get_heapptr_default(duk_hthread *thr, duk_idx_t idx, void *def_value) {
	void *ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = duk_get_heapptr(thr, idx);
	if (ret != NULL) {
		return ret;
	}

	return def_value;
}

DUK_EXTERNAL void *duk_require_heapptr(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	void *ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_UNLIKELY(!DUK_TVAL_IS_HEAP_ALLOCATED(tv))) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "heapobject", DUK_STR_UNEXPECTED_TYPE);
		DUK_WO_NORETURN(return NULL;);
	}

	ret = (void *) DUK_TVAL_GET_HEAPHDR(tv);
	DUK_ASSERT(ret != NULL);
	return ret;
}

/* Internal helper for getting/requiring a duk_hobject with possible promotion. */
DUK_LOCAL duk_hobject *duk__get_hobject_promote_mask_raw(duk_hthread *thr, duk_idx_t idx, duk_uint_t type_mask) {
	duk_uint_t val_mask;
	duk_hobject *res;

	DUK_CTX_ASSERT_VALID(thr);

	res = duk_get_hobject(thr, idx);  /* common case, not promoted */
	if (DUK_LIKELY(res != NULL)) {
		DUK_ASSERT(res != NULL);
		return res;
	}

	val_mask = duk_get_type_mask(thr, idx);
	if (val_mask & type_mask) {
		if (type_mask & DUK_TYPE_MASK_PROMOTE) {
			res = duk_to_hobject(thr, idx);
			DUK_ASSERT(res != NULL);
			return res;
		} else {
			return NULL;  /* accept without promoting */
		}
	}

	if (type_mask & DUK_TYPE_MASK_THROW) {
		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, "object", DUK_STR_NOT_OBJECT);
		DUK_WO_NORETURN(return NULL;);
	}
	return NULL;
}

/* Get a duk_hobject * at 'idx'; if the value is not an object but matches the
 * supplied 'type_mask', promote it to an object and return the duk_hobject *.
 * This is useful for call sites which want an object but also accept a plain
 * buffer and/or a lightfunc which gets automatically promoted to an object.
 * Return value is NULL if value is neither an object nor a plain type allowed
 * by the mask.
 */
DUK_INTERNAL duk_hobject *duk_get_hobject_promote_mask(duk_hthread *thr, duk_idx_t idx, duk_uint_t type_mask) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_hobject_promote_mask_raw(thr, idx, type_mask | DUK_TYPE_MASK_PROMOTE);
}

/* Like duk_get_hobject_promote_mask() but throw a TypeError instead of
 * returning a NULL.
 */
DUK_INTERNAL duk_hobject *duk_require_hobject_promote_mask(duk_hthread *thr, duk_idx_t idx, duk_uint_t type_mask) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_hobject_promote_mask_raw(thr, idx, type_mask | DUK_TYPE_MASK_THROW | DUK_TYPE_MASK_PROMOTE);
}

/* Require a duk_hobject * at 'idx'; if the value is not an object but matches the
 * supplied 'type_mask', return a NULL instead.  Otherwise throw a TypeError.
 */
DUK_INTERNAL duk_hobject *duk_require_hobject_accept_mask(duk_hthread *thr, duk_idx_t idx, duk_uint_t type_mask) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__get_hobject_promote_mask_raw(thr, idx, type_mask | DUK_TYPE_MASK_THROW);
}

DUK_INTERNAL duk_hobject *duk_get_hobject_with_class(duk_hthread *thr, duk_idx_t idx, duk_small_uint_t classnum) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT_DISABLE(classnum >= 0);  /* unsigned */
	DUK_ASSERT(classnum <= DUK_HOBJECT_CLASS_MAX);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(h != NULL && DUK_HOBJECT_GET_CLASS_NUMBER(h) != classnum)) {
		h = NULL;
	}
	return h;
}

DUK_INTERNAL duk_hobject *duk_require_hobject_with_class(duk_hthread *thr, duk_idx_t idx, duk_small_uint_t classnum) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT_DISABLE(classnum >= 0);  /* unsigned */
	DUK_ASSERT(classnum <= DUK_HOBJECT_CLASS_MAX);

	h = (duk_hobject *) duk__get_tagged_heaphdr_raw(thr, idx, DUK_TAG_OBJECT);
	if (DUK_UNLIKELY(!(h != NULL && DUK_HOBJECT_GET_CLASS_NUMBER(h) == classnum))) {
		duk_hstring *h_class;
		h_class = DUK_HTHREAD_GET_STRING(thr, DUK_HOBJECT_CLASS_NUMBER_TO_STRIDX(classnum));
		DUK_UNREF(h_class);

		DUK_ERROR_REQUIRE_TYPE_INDEX(thr, idx, (const char *) DUK_HSTRING_GET_DATA(h_class), DUK_STR_UNEXPECTED_TYPE);
		DUK_WO_NORETURN(return NULL;);
	}
	return h;
}

DUK_EXTERNAL duk_size_t duk_get_length(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_UNDEFINED:
	case DUK_TAG_NULL:
	case DUK_TAG_BOOLEAN:
	case DUK_TAG_POINTER:
		return 0;
#if defined(DUK_USE_PREFER_SIZE)
	/* String and buffer have a virtual non-configurable .length property
	 * which is within size_t range so it can be looked up without specific
	 * type checks.  Lightfuncs inherit from %NativeFunctionPrototype%
	 * which provides an inherited .length accessor; it could be overwritten
	 * to produce unexpected types or values, but just number convert and
	 * duk_size_t cast for now.
	 */
	case DUK_TAG_STRING:
	case DUK_TAG_BUFFER:
	case DUK_TAG_LIGHTFUNC: {
		duk_size_t ret;
		duk_get_prop_stridx(thr, idx, DUK_STRIDX_LENGTH);
		ret = (duk_size_t) duk_to_number_m1(thr);
		duk_pop_unsafe(thr);
		return ret;
	}
#else  /* DUK_USE_PREFER_SIZE */
	case DUK_TAG_STRING: {
		duk_hstring *h = DUK_TVAL_GET_STRING(tv);
		DUK_ASSERT(h != NULL);
		if (DUK_UNLIKELY(DUK_HSTRING_HAS_SYMBOL(h))) {
			return 0;
		}
		return (duk_size_t) DUK_HSTRING_GET_CHARLEN(h);
	}
	case DUK_TAG_BUFFER: {
		duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h != NULL);
		return (duk_size_t) DUK_HBUFFER_GET_SIZE(h);
	}
	case DUK_TAG_LIGHTFUNC: {
		/* We could look up the length from the lightfunc duk_tval,
		 * but since Duktape 2.2 lightfunc .length comes from
		 * %NativeFunctionPrototype% which can be overridden, so
		 * look up the property explicitly.
		 */
		duk_size_t ret;
		duk_get_prop_stridx(thr, idx, DUK_STRIDX_LENGTH);
		ret = (duk_size_t) duk_to_number_m1(thr);
		duk_pop_unsafe(thr);
		return ret;
	}
#endif  /* DUK_USE_PREFER_SIZE */
	case DUK_TAG_OBJECT: {
		duk_hobject *h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		return (duk_size_t) duk_hobject_get_length(thr, h);
	}
#if defined(DUK_USE_FASTINT)
	case DUK_TAG_FASTINT:
#endif
	default:
		/* number or 'unused' */
		DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv) || DUK_TVAL_IS_UNUSED(tv));
		return 0;
	}

	DUK_UNREACHABLE();
}

/*
 *  duk_known_xxx() helpers
 *
 *  Used internally when we're 100% sure that a certain index is valid and
 *  contains an object of a certain type.  For example, if we duk_push_object()
 *  we can then safely duk_known_hobject(thr, -1).  These helpers just assert
 *  for the index and type, and if the assumptions are not valid, memory unsafe
 *  behavior happens.
 */

DUK_LOCAL duk_heaphdr *duk__known_heaphdr(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_heaphdr *h;

	DUK_CTX_ASSERT_VALID(thr);
	if (idx < 0) {
		tv = thr->valstack_top + idx;
	} else {
		tv = thr->valstack_bottom + idx;
	}
	DUK_ASSERT(tv >= thr->valstack_bottom);
	DUK_ASSERT(tv < thr->valstack_top);
	h = DUK_TVAL_GET_HEAPHDR(tv);
	DUK_ASSERT(h != NULL);
	return h;
}

DUK_INTERNAL duk_hstring *duk_known_hstring(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(duk_get_hstring(thr, idx) != NULL);
	return (duk_hstring *) duk__known_heaphdr(thr, idx);
}

DUK_INTERNAL duk_hobject *duk_known_hobject(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(duk_get_hobject(thr, idx) != NULL);
	return (duk_hobject *) duk__known_heaphdr(thr, idx);
}

DUK_INTERNAL duk_hbuffer *duk_known_hbuffer(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(duk_get_hbuffer(thr, idx) != NULL);
	return (duk_hbuffer *) duk__known_heaphdr(thr, idx);
}

DUK_INTERNAL duk_hcompfunc *duk_known_hcompfunc(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(duk_get_hcompfunc(thr, idx) != NULL);
	return (duk_hcompfunc *) duk__known_heaphdr(thr, idx);
}

DUK_INTERNAL duk_hnatfunc *duk_known_hnatfunc(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(duk_get_hnatfunc(thr, idx) != NULL);
	return (duk_hnatfunc *) duk__known_heaphdr(thr, idx);
}

DUK_EXTERNAL void duk_set_length(duk_hthread *thr, duk_idx_t idx, duk_size_t len) {
	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_normalize_index(thr, idx);
	duk_push_uint(thr, (duk_uint_t) len);
	duk_put_prop_stridx(thr, idx, DUK_STRIDX_LENGTH);
}

/*
 *  Conversions and coercions
 *
 *  The conversion/coercions are in-place operations on the value stack.
 *  Some operations are implemented here directly, while others call a
 *  helper in duk_js_ops.c after validating arguments.
 */

/* E5 Section 8.12.8 */

DUK_LOCAL duk_bool_t duk__defaultvalue_coerce_attempt(duk_hthread *thr, duk_idx_t idx, duk_small_uint_t func_stridx) {
	if (duk_get_prop_stridx(thr, idx, func_stridx)) {
		/* [ ... func ] */
		if (duk_is_callable(thr, -1)) {
			duk_dup(thr, idx);         /* -> [ ... func this ] */
			duk_call_method(thr, 0);     /* -> [ ... retval ] */
			if (duk_is_primitive(thr, -1)) {
				duk_replace(thr, idx);
				return 1;
			}
			/* [ ... retval ]; popped below */
		}
	}
	duk_pop_unsafe(thr);  /* [ ... func/retval ] -> [ ... ] */
	return 0;
}

DUK_EXTERNAL void duk_to_undefined(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);
	DUK_TVAL_SET_UNDEFINED_UPDREF(thr, tv);  /* side effects */
}

DUK_EXTERNAL void duk_to_null(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);
	DUK_TVAL_SET_NULL_UPDREF(thr, tv);  /* side effects */
}

/* E5 Section 9.1 */
DUK_LOCAL const char * const duk__toprim_hint_strings[3] = {
	"default", "string", "number"
};
DUK_LOCAL void duk__to_primitive_helper(duk_hthread *thr, duk_idx_t idx, duk_int_t hint, duk_bool_t check_symbol) {
	/* Inline initializer for coercers[] is not allowed by old compilers like BCC. */
	duk_small_uint_t coercers[2];

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(hint == DUK_HINT_NONE || hint == DUK_HINT_NUMBER || hint == DUK_HINT_STRING);

	idx = duk_require_normalize_index(thr, idx);

	/* If already primitive, return as is. */
	if (!duk_check_type_mask(thr, idx, DUK_TYPE_MASK_OBJECT |
	                                   DUK_TYPE_MASK_LIGHTFUNC |
	                                   DUK_TYPE_MASK_BUFFER)) {
		DUK_ASSERT(!duk_is_buffer(thr, idx));  /* duk_to_string() relies on this behavior */
		return;
	}

	/* @@toPrimitive lookup.  Also do for plain buffers and lightfuncs
	 * which mimic objects.
	 */
	if (check_symbol && duk_get_method_stridx(thr, idx, DUK_STRIDX_WELLKNOWN_SYMBOL_TO_PRIMITIVE)) {
		DUK_ASSERT(hint >= 0 && (duk_size_t) hint < sizeof(duk__toprim_hint_strings) / sizeof(const char *));
		duk_dup(thr, idx);
		duk_push_string(thr, duk__toprim_hint_strings[hint]);
		duk_call_method(thr, 1);  /* [ ... method value hint ] -> [ ... res] */
		if (duk_check_type_mask(thr, -1, DUK_TYPE_MASK_OBJECT |
	                                         DUK_TYPE_MASK_LIGHTFUNC |
		                                 DUK_TYPE_MASK_BUFFER)) {
			goto fail;
		}
		duk_replace(thr, idx);
		return;
	}

	/* Objects are coerced based on E5 specification.
	 * Lightfuncs are coerced because they behave like
	 * objects even if they're internally a primitive
	 * type.  Same applies to plain buffers, which behave
	 * like ArrayBuffer objects since Duktape 2.x.
	 */

	/* Hint magic for Date is unnecessary in ES2015 because of
	 * Date.prototype[@@toPrimitive].  However, it is needed if
	 * symbol support is not enabled.
	 */
#if defined(DUK_USE_SYMBOL_BUILTIN)
	if (hint == DUK_HINT_NONE) {
		hint = DUK_HINT_NUMBER;
	}
#else  /* DUK_USE_SYMBOL_BUILTIN */
	if (hint == DUK_HINT_NONE) {
		duk_small_uint_t class_number;

		class_number = duk_get_class_number(thr, idx);
		if (class_number == DUK_HOBJECT_CLASS_DATE) {
			hint = DUK_HINT_STRING;
		} else {
			hint = DUK_HINT_NUMBER;
		}
	}
#endif  /* DUK_USE_SYMBOL_BUILTIN */

	coercers[0] = DUK_STRIDX_VALUE_OF;
	coercers[1] = DUK_STRIDX_TO_STRING;
	if (hint == DUK_HINT_STRING) {
		coercers[0] = DUK_STRIDX_TO_STRING;
		coercers[1] = DUK_STRIDX_VALUE_OF;
	}

	if (duk__defaultvalue_coerce_attempt(thr, idx, coercers[0])) {
		DUK_ASSERT(!duk_is_buffer(thr, idx));  /* duk_to_string() relies on this behavior */
		return;
	}

	if (duk__defaultvalue_coerce_attempt(thr, idx, coercers[1])) {
		DUK_ASSERT(!duk_is_buffer(thr, idx));  /* duk_to_string() relies on this behavior */
		return;
	}

 fail:
	DUK_ERROR_TYPE(thr, DUK_STR_TOPRIMITIVE_FAILED);
	DUK_WO_NORETURN(return;);
}

DUK_EXTERNAL void duk_to_primitive(duk_hthread *thr, duk_idx_t idx, duk_int_t hint) {
	duk__to_primitive_helper(thr, idx, hint, 1 /*check_symbol*/);
}

#if defined(DUK_USE_SYMBOL_BUILTIN)
DUK_INTERNAL void duk_to_primitive_ordinary(duk_hthread *thr, duk_idx_t idx, duk_int_t hint) {
	duk__to_primitive_helper(thr, idx, hint, 0 /*check_symbol*/);
}
#endif

/* E5 Section 9.2 */
DUK_EXTERNAL duk_bool_t duk_to_boolean(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_bool_t val;

	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);
	tv = DUK_GET_TVAL_POSIDX(thr, idx);
	DUK_ASSERT(tv != NULL);

	val = duk_js_toboolean(tv);
	DUK_ASSERT(val == 0 || val == 1);

	/* Note: no need to re-lookup tv, conversion is side effect free. */
	DUK_ASSERT(tv != NULL);
	DUK_TVAL_SET_BOOLEAN_UPDREF(thr, tv, val);  /* side effects */
	return val;
}

DUK_INTERNAL duk_bool_t duk_to_boolean_top_pop(duk_hthread *thr) {
	duk_tval *tv;
	duk_bool_t val;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, -1);
	DUK_ASSERT(tv != NULL);

	val = duk_js_toboolean(tv);
	DUK_ASSERT(val == 0 || val == 1);

	duk_pop_unsafe(thr);
	return val;
}

DUK_EXTERNAL duk_double_t duk_to_number(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_double_t d;

	DUK_ASSERT_API_ENTRY(thr);

	/* XXX: No need to normalize; the whole operation could be inlined here to
	 * avoid 'tv' re-lookup.
	 */
	idx = duk_require_normalize_index(thr, idx);
	tv = DUK_GET_TVAL_POSIDX(thr, idx);
	DUK_ASSERT(tv != NULL);
	d = duk_js_tonumber(thr, tv);  /* XXX: fastint coercion? now result will always be a non-fastint */

	/* ToNumber() may have side effects so must relookup 'tv'. */
	tv = DUK_GET_TVAL_POSIDX(thr, idx);
	DUK_TVAL_SET_NUMBER_UPDREF(thr, tv, d);  /* side effects */
	return d;
}

DUK_INTERNAL duk_double_t duk_to_number_m1(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_to_number(thr, -1);
}
DUK_INTERNAL duk_double_t duk_to_number_m2(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_to_number(thr, -2);
}

DUK_INTERNAL duk_double_t duk_to_number_tval(duk_hthread *thr, duk_tval *tv) {
#if defined(DUK_USE_PREFER_SIZE)
	duk_double_t res;

	DUK_ASSERT_API_ENTRY(thr);

	duk_push_tval(thr, tv);
	res = duk_to_number_m1(thr);
	duk_pop_unsafe(thr);
	return res;
#else
	duk_double_t res;
	duk_tval *tv_dst;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__ASSERT_SPACE();

	tv_dst = thr->valstack_top++;
	DUK_TVAL_SET_TVAL(tv_dst, tv);
	DUK_TVAL_INCREF(thr, tv_dst);  /* decref not necessary */
	res = duk_to_number_m1(thr);  /* invalidates tv_dst */

	tv_dst = --thr->valstack_top;
	DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv_dst));
	DUK_ASSERT(!DUK_TVAL_NEEDS_REFCOUNT_UPDATE(tv_dst));  /* plain number */
	DUK_TVAL_SET_UNDEFINED(tv_dst);  /* valstack init policy */

	return res;
#endif
}

/* XXX: combine all the integer conversions: they share everything
 * but the helper function for coercion.
 */

typedef duk_double_t (*duk__toint_coercer)(duk_hthread *thr, duk_tval *tv);

DUK_LOCAL duk_double_t duk__to_int_uint_helper(duk_hthread *thr, duk_idx_t idx, duk__toint_coercer coerce_func) {
	duk_tval *tv;
	duk_double_t d;

	DUK_CTX_ASSERT_VALID(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);

#if defined(DUK_USE_FASTINT)
	/* If argument is a fastint, guarantee that it remains one.
	 * There's no downgrade check for other cases.
	 */
	if (DUK_TVAL_IS_FASTINT(tv)) {
		/* XXX: Unnecessary conversion back and forth. */
		return (duk_double_t) DUK_TVAL_GET_FASTINT(tv);
	}
#endif
	d = coerce_func(thr, tv);

	/* XXX: fastint? */

	/* Relookup in case coerce_func() has side effects, e.g. ends up coercing an object */
	tv = duk_require_tval(thr, idx);
	DUK_TVAL_SET_NUMBER_UPDREF(thr, tv, d);  /* side effects */
	return d;
}

DUK_EXTERNAL duk_int_t duk_to_int(duk_hthread *thr, duk_idx_t idx) {
	/* Value coercion (in stack): ToInteger(), E5 Section 9.4,
	 * API return value coercion: custom.
	 */
	DUK_ASSERT_API_ENTRY(thr);
	(void) duk__to_int_uint_helper(thr, idx, duk_js_tointeger);
	return (duk_int_t) duk__api_coerce_d2i(thr, idx, 0 /*def_value*/, 0 /*require*/);
}

DUK_EXTERNAL duk_uint_t duk_to_uint(duk_hthread *thr, duk_idx_t idx) {
	/* Value coercion (in stack): ToInteger(), E5 Section 9.4,
	 * API return value coercion: custom.
	 */
	DUK_ASSERT_API_ENTRY(thr);
	(void) duk__to_int_uint_helper(thr, idx, duk_js_tointeger);
	return (duk_uint_t) duk__api_coerce_d2ui(thr, idx, 0 /*def_value*/, 0 /*require*/);
}

DUK_EXTERNAL duk_int32_t duk_to_int32(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_int32_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);
	ret = duk_js_toint32(thr, tv);

	/* Relookup in case coerce_func() has side effects, e.g. ends up coercing an object */
	tv = duk_require_tval(thr, idx);
	DUK_TVAL_SET_I32_UPDREF(thr, tv, ret);  /* side effects */
	return ret;
}

DUK_EXTERNAL duk_uint32_t duk_to_uint32(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_uint32_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);
	ret = duk_js_touint32(thr, tv);

	/* Relookup in case coerce_func() has side effects, e.g. ends up coercing an object */
	tv = duk_require_tval(thr, idx);
	DUK_TVAL_SET_U32_UPDREF(thr, tv, ret);  /* side effects */
	return ret;
}

DUK_EXTERNAL duk_uint16_t duk_to_uint16(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_uint16_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);
	ret = duk_js_touint16(thr, tv);

	/* Relookup in case coerce_func() has side effects, e.g. ends up coercing an object */
	tv = duk_require_tval(thr, idx);
	DUK_TVAL_SET_U32_UPDREF(thr, tv, ret);  /* side effects */
	return ret;
}

#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
/* Special coercion for Uint8ClampedArray. */
DUK_INTERNAL duk_uint8_t duk_to_uint8clamped(duk_hthread *thr, duk_idx_t idx) {
	duk_double_t d;
	duk_double_t t;
	duk_uint8_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	/* XXX: Simplify this algorithm, should be possible to come up with
	 * a shorter and faster algorithm by inspecting IEEE representation
	 * directly.
	 */

	d = duk_to_number(thr, idx);
	if (d <= 0.0) {
		return 0;
	} else if (d >= 255) {
		return 255;
	} else if (DUK_ISNAN(d)) {
		/* Avoid NaN-to-integer coercion as it is compiler specific. */
		return 0;
	}

	t = d - DUK_FLOOR(d);
	if (duk_double_equals(t, 0.5)) {
		/* Exact halfway, round to even. */
		ret = (duk_uint8_t) d;
		ret = (ret + 1) & 0xfe;  /* Example: d=3.5, t=0.5 -> ret = (3 + 1) & 0xfe = 4 & 0xfe = 4
		                          * Example: d=4.5, t=0.5 -> ret = (4 + 1) & 0xfe = 5 & 0xfe = 4
		                          */
	} else {
		/* Not halfway, round to nearest. */
		ret = (duk_uint8_t) (d + 0.5);
	}
	return ret;
}
#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */

DUK_EXTERNAL const char *duk_to_lstring(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len) {
	DUK_ASSERT_API_ENTRY(thr);

	(void) duk_to_string(thr, idx);
	DUK_ASSERT(duk_is_string(thr, idx));
	return duk_require_lstring(thr, idx, out_len);
}

DUK_LOCAL duk_ret_t duk__safe_to_string_raw(duk_hthread *thr, void *udata) {
	DUK_CTX_ASSERT_VALID(thr);
	DUK_UNREF(udata);

	(void) duk_to_string(thr, -1);
	return 1;
}

DUK_EXTERNAL const char *duk_safe_to_lstring(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_len) {
	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);

	/* We intentionally ignore the duk_safe_call() return value and only
	 * check the output type.  This way we don't also need to check that
	 * the returned value is indeed a string in the success case.
	 */

	duk_dup(thr, idx);
	(void) duk_safe_call(thr, duk__safe_to_string_raw, NULL /*udata*/, 1 /*nargs*/, 1 /*nrets*/);
	if (!duk_is_string(thr, -1)) {
		/* Error: try coercing error to string once. */
		(void) duk_safe_call(thr, duk__safe_to_string_raw, NULL /*udata*/, 1 /*nargs*/, 1 /*nrets*/);
		if (!duk_is_string(thr, -1)) {
			/* Double error */
			duk_pop_unsafe(thr);
			duk_push_hstring_stridx(thr, DUK_STRIDX_UC_ERROR);
		} else {
			;
		}
	} else {
		/* String; may be a symbol, accepted. */
		;
	}
	DUK_ASSERT(duk_is_string(thr, -1));

	duk_replace(thr, idx);
	DUK_ASSERT(duk_get_string(thr, idx) != NULL);
	return duk_get_lstring(thr, idx, out_len);
}

DUK_EXTERNAL const char *duk_to_stacktrace(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	idx = duk_require_normalize_index(thr, idx);

	/* The expected argument to the call is an Error object.  The stack
	 * trace is extracted without an inheritance-based instanceof check
	 * so that one can also extract the stack trace of a foreign error
	 * created in another Realm.  Accept only a string .stack property.
	 */
	if (duk_is_object(thr, idx)) {
		(void) duk_get_prop_string(thr, idx, "stack");
		if (duk_is_string(thr, -1)) {
			duk_replace(thr, idx);
		} else {
			duk_pop(thr);
		}
	}

	return duk_to_string(thr, idx);
}

DUK_LOCAL duk_ret_t duk__safe_to_stacktrace_raw(duk_hthread *thr, void *udata) {
	DUK_CTX_ASSERT_VALID(thr);
	DUK_UNREF(udata);

	(void) duk_to_stacktrace(thr, -1);

	return 1;
}

DUK_EXTERNAL const char *duk_safe_to_stacktrace(duk_hthread *thr, duk_idx_t idx) {
	duk_int_t rc;

	DUK_ASSERT_API_ENTRY(thr);
	idx = duk_require_normalize_index(thr, idx);

	duk_dup(thr, idx);
	rc = duk_safe_call(thr, duk__safe_to_stacktrace_raw, NULL /*udata*/, 1 /*nargs*/, 1 /*nrets*/);
	if (rc != 0) {
		/* Coercion failed.  Try to coerce the coercion itself error
		 * to a stack trace once.  If that also fails, return a fixed,
		 * preallocated 'Error' string to avoid potential infinite loop.
		 */
		rc = duk_safe_call(thr, duk__safe_to_stacktrace_raw, NULL /*udata*/, 1 /*nargs*/, 1 /*nrets*/);
		if (rc != 0) {
			duk_pop_unsafe(thr);
			duk_push_hstring_stridx(thr, DUK_STRIDX_UC_ERROR);
		}
	}
	duk_replace(thr, idx);

	return duk_get_string(thr, idx);
}

DUK_INTERNAL duk_hstring *duk_to_property_key_hstring(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);

	duk_to_primitive(thr, idx, DUK_HINT_STRING);  /* needed for e.g. Symbol objects */
	h = duk_get_hstring(thr, idx);
	if (h == NULL) {
		/* The "is string?" check may seem unnecessary, but as things
		 * are duk_to_hstring() invokes ToString() which fails for
		 * symbols.  But since symbols are already strings for Duktape
		 * C API, we check for that before doing the coercion.
		 */
		h = duk_to_hstring(thr, idx);
	}
	DUK_ASSERT(h != NULL);
	return h;
}

#if defined(DUK_USE_DEBUGGER_SUPPORT)  /* only needed by debugger for now */
DUK_INTERNAL duk_hstring *duk_safe_to_hstring(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	(void) duk_safe_to_string(thr, idx);
	DUK_ASSERT(duk_is_string(thr, idx));
	DUK_ASSERT(duk_get_hstring(thr, idx) != NULL);
	return duk_known_hstring(thr, idx);
}
#endif

/* Push Object.prototype.toString() output for 'tv'. */
DUK_INTERNAL void duk_push_class_string_tval(duk_hthread *thr, duk_tval *tv, duk_bool_t avoid_side_effects) {
	duk_hobject *h_obj;
	duk_small_uint_t classnum;
	duk_small_uint_t stridx;
	duk_tval tv_tmp;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(tv != NULL);

	/* Stabilize 'tv', duk_push_literal() may trigger side effects. */
	DUK_TVAL_SET_TVAL(&tv_tmp, tv);
	tv = &tv_tmp;

	/* Conceptually for any non-undefined/null value we should do a
	 * ToObject() coercion and look up @@toStringTag (from the object
	 * prototype) to see if a custom result should be used, with the
	 * exception of Arrays which are handled specially first.
	 *
	 * We'd like to avoid the actual conversion, but even for primitive
	 * types the prototype may have @@toStringTag.  What's worse, the
	 * @@toStringTag property may be a getter that must get the object
	 * coerced value (not the prototype) as its 'this' binding.
	 *
	 * For now, do an actual object coercion.  This could be avoided by
	 * doing a side effect free lookup to see if a getter would be invoked.
	 * If not, the value can be read directly and the object coercion could
	 * be avoided.  This may not be worth it in practice, because
	 * Object.prototype.toString() is usually not performance critical.
	 */

	duk_push_literal(thr, "[object ");  /* -> [ ... "[object" ] */

	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_UNUSED:  /* Treat like 'undefined', shouldn't happen. */
	case DUK_TAG_UNDEFINED: {
		duk_push_hstring_stridx(thr, DUK_STRIDX_UC_UNDEFINED);
		goto finish;
	}
	case DUK_TAG_NULL: {
		duk_push_hstring_stridx(thr, DUK_STRIDX_UC_NULL);
		goto finish;
	}
	}

	duk_push_tval(thr, tv);
	tv = NULL;  /* Invalidated by ToObject(). */
	h_obj = duk_to_hobject(thr, -1);
	DUK_ASSERT(h_obj != NULL);
	if (duk_js_isarray_hobject(h_obj)) {
		stridx = DUK_STRIDX_UC_ARRAY;
	} else {
		/* [ ... "[object" obj ] */

#if defined(DUK_USE_SYMBOL_BUILTIN)
		/* XXX: better handling with avoid_side_effects == 1; lookup tval
		 * without Proxy or getter side effects, and use it in sanitized
		 * form if it's a string.
		 */
		if (!avoid_side_effects) {
			(void) duk_get_prop_stridx(thr, -1, DUK_STRIDX_WELLKNOWN_SYMBOL_TO_STRING_TAG);
			if (duk_is_string_notsymbol(thr, -1)) {
				duk_remove_m2(thr);
				goto finish;
			}
			duk_pop_unsafe(thr);
		}
#else
		DUK_UNREF(avoid_side_effects);
#endif

		classnum = DUK_HOBJECT_GET_CLASS_NUMBER(h_obj);
		stridx = DUK_HOBJECT_CLASS_NUMBER_TO_STRIDX(classnum);
	}
	duk_pop_unsafe(thr);
	duk_push_hstring_stridx(thr, stridx);

 finish:
	/* [ ... "[object" tag ] */
	duk_push_literal(thr, "]");
	duk_concat(thr, 3);  /* [ ... "[object" tag "]" ] -> [ ... res ] */
}

/* XXX: other variants like uint, u32 etc */
DUK_INTERNAL duk_int_t duk_to_int_clamped_raw(duk_hthread *thr, duk_idx_t idx, duk_int_t minval, duk_int_t maxval, duk_bool_t *out_clamped) {
	duk_tval *tv;
	duk_tval tv_tmp;
	duk_double_t d, dmin, dmax;
	duk_int_t res;
	duk_bool_t clamped = 0;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	DUK_ASSERT(tv != NULL);
	d = duk_js_tointeger(thr, tv);  /* E5 Section 9.4, ToInteger() */

	dmin = (duk_double_t) minval;
	dmax = (duk_double_t) maxval;

	if (d < dmin) {
		clamped = 1;
		res = minval;
		d = dmin;
	} else if (d > dmax) {
		clamped = 1;
		res = maxval;
		d = dmax;
	} else {
		res = (duk_int_t) d;
	}
	DUK_UNREF(d);  /* SCANBUILD: with suitable dmin/dmax limits 'd' is unused */
	/* 'd' and 'res' agree here */

	/* Relookup in case duk_js_tointeger() ends up e.g. coercing an object. */
	tv = duk_get_tval(thr, idx);
	DUK_ASSERT(tv != NULL);  /* not popped by side effect */
	DUK_TVAL_SET_TVAL(&tv_tmp, tv);
#if defined(DUK_USE_FASTINT)
#if (DUK_INT_MAX <= 0x7fffffffL)
	DUK_TVAL_SET_I32(tv, res);
#else
	/* Clamping needed if duk_int_t is 64 bits. */
	if (res >= DUK_FASTINT_MIN && res <= DUK_FASTINT_MAX) {
		DUK_TVAL_SET_FASTINT(tv, res);
	} else {
		DUK_TVAL_SET_NUMBER(tv, d);
	}
#endif
#else
	DUK_TVAL_SET_NUMBER(tv, d);  /* no need to incref */
#endif
	DUK_TVAL_DECREF(thr, &tv_tmp);  /* side effects */

	if (out_clamped) {
		*out_clamped = clamped;
	} else {
		/* coerced value is updated to value stack even when RangeError thrown */
		if (clamped) {
			DUK_ERROR_RANGE(thr, DUK_STR_NUMBER_OUTSIDE_RANGE);
			DUK_WO_NORETURN(return 0;);
		}
	}

	return res;
}

DUK_INTERNAL duk_int_t duk_to_int_clamped(duk_hthread *thr, duk_idx_t idx, duk_idx_t minval, duk_idx_t maxval) {
	duk_bool_t dummy;

	DUK_ASSERT_API_ENTRY(thr);

	return duk_to_int_clamped_raw(thr, idx, minval, maxval, &dummy);
}

DUK_INTERNAL duk_int_t duk_to_int_check_range(duk_hthread *thr, duk_idx_t idx, duk_int_t minval, duk_int_t maxval) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_to_int_clamped_raw(thr, idx, minval, maxval, NULL);  /* out_clamped==NULL -> RangeError if outside range */
}

DUK_EXTERNAL const char *duk_to_string(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);
	tv = DUK_GET_TVAL_POSIDX(thr, idx);
	DUK_ASSERT(tv != NULL);

	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_UNDEFINED: {
		duk_push_hstring_stridx(thr, DUK_STRIDX_LC_UNDEFINED);
		break;
	}
	case DUK_TAG_NULL: {
		duk_push_hstring_stridx(thr, DUK_STRIDX_LC_NULL);
		break;
	}
	case DUK_TAG_BOOLEAN: {
		if (DUK_TVAL_GET_BOOLEAN(tv)) {
			duk_push_hstring_stridx(thr, DUK_STRIDX_TRUE);
		} else {
			duk_push_hstring_stridx(thr, DUK_STRIDX_FALSE);
		}
		break;
	}
	case DUK_TAG_STRING: {
		/* Nop for actual strings, TypeError for Symbols.
		 * Because various internals rely on ToString() coercion of
		 * internal strings, -allow- (NOP) string coercion for hidden
		 * symbols.
		 */
#if 1
		duk_hstring *h;
		h = DUK_TVAL_GET_STRING(tv);
		DUK_ASSERT(h != NULL);
		if (DUK_UNLIKELY(DUK_HSTRING_HAS_SYMBOL(h))) {
			DUK_ERROR_TYPE(thr, DUK_STR_CANNOT_STRING_COERCE_SYMBOL);
			DUK_WO_NORETURN(goto skip_replace;);
		} else {
			goto skip_replace;
		}
#else
		goto skip_replace;
#endif
		break;
	}
	case DUK_TAG_BUFFER: /* Go through Uint8Array.prototype.toString() for coercion. */
	case DUK_TAG_OBJECT: {
		/* Plain buffers: go through ArrayBuffer.prototype.toString()
		 * for coercion.
		 *
		 * Symbol objects: duk_to_primitive() results in a plain symbol
		 * value, and duk_to_string() then causes a TypeError.
		 */
		duk_to_primitive(thr, idx, DUK_HINT_STRING);
		DUK_ASSERT(!duk_is_buffer(thr, idx));  /* ToPrimitive() must guarantee */
		DUK_ASSERT(!duk_is_object(thr, idx));
		return duk_to_string(thr, idx);  /* Note: recursive call */
	}
	case DUK_TAG_POINTER: {
		void *ptr = DUK_TVAL_GET_POINTER(tv);
		if (ptr != NULL) {
			duk_push_sprintf(thr, DUK_STR_FMT_PTR, (void *) ptr);
		} else {
			/* Represent a null pointer as 'null' to be consistent with
			 * the JX format variant.  Native '%p' format for a NULL
			 * pointer may be e.g. '(nil)'.
			 */
			duk_push_hstring_stridx(thr, DUK_STRIDX_LC_NULL);
		}
		break;
	}
	case DUK_TAG_LIGHTFUNC: {
		/* Should match Function.prototype.toString() */
		duk_push_lightfunc_tostring(thr, tv);
		break;
	}
#if defined(DUK_USE_FASTINT)
	case DUK_TAG_FASTINT:
#endif
	default: {
		/* number */
		DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
		DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv));
		duk_push_tval(thr, tv);
		duk_numconv_stringify(thr,
		                      10 /*radix*/,
		                      0 /*precision:shortest*/,
		                      0 /*force_exponential*/);
		break;
	}
	}

	duk_replace(thr, idx);

 skip_replace:
	DUK_ASSERT(duk_is_string(thr, idx));
	return duk_require_string(thr, idx);
}

DUK_INTERNAL duk_hstring *duk_to_hstring(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *ret;

	DUK_ASSERT_API_ENTRY(thr);

	duk_to_string(thr, idx);
	ret = duk_get_hstring(thr, idx);
	DUK_ASSERT(ret != NULL);
	return ret;
}

DUK_INTERNAL duk_hstring *duk_to_hstring_m1(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_to_hstring(thr, -1);
}

DUK_INTERNAL duk_hstring *duk_to_hstring_acceptsymbol(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *ret;

	DUK_ASSERT_API_ENTRY(thr);

	ret = duk_get_hstring(thr, idx);
	if (DUK_UNLIKELY(ret && DUK_HSTRING_HAS_SYMBOL(ret))) {
		return ret;
	}
	return duk_to_hstring(thr, idx);
}

/* Convert a plain buffer or any buffer object into a string, using the buffer
 * bytes 1:1 in the internal string representation.  For views the active byte
 * slice (not element slice interpreted as an initializer) is used.  This is
 * necessary in Duktape 2.x because ToString(plainBuffer) no longer creates a
 * string with the same bytes as in the buffer but rather (usually)
 * '[object ArrayBuffer]'.
 */
DUK_EXTERNAL const char *duk_buffer_to_string(duk_hthread *thr, duk_idx_t idx) {
	void *ptr_src;
	duk_size_t len;
	const char *res;

	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);

	ptr_src = duk_require_buffer_data(thr, idx, &len);
	DUK_ASSERT(ptr_src != NULL || len == 0);

	res = duk_push_lstring(thr, (const char *) ptr_src, len);
	duk_replace(thr, idx);
	return res;
}

DUK_EXTERNAL void *duk_to_buffer_raw(duk_hthread *thr, duk_idx_t idx, duk_size_t *out_size, duk_uint_t mode) {
	duk_hbuffer *h_buf;
	const duk_uint8_t *src_data;
	duk_size_t src_size;
	duk_uint8_t *dst_data;

	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);

	h_buf = duk_get_hbuffer(thr, idx);
	if (h_buf != NULL) {
		/* Buffer is kept as is, with the fixed/dynamic nature of the
		 * buffer only changed if requested.  An external buffer
		 * is converted into a non-external dynamic buffer in a
		 * duk_to_dynamic_buffer() call.
		 */
		duk_uint_t tmp;
		duk_uint8_t *tmp_ptr;

		tmp_ptr = (duk_uint8_t *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h_buf);
		src_data = (const duk_uint8_t *) tmp_ptr;
		src_size = DUK_HBUFFER_GET_SIZE(h_buf);

		tmp = (DUK_HBUFFER_HAS_DYNAMIC(h_buf) ? DUK_BUF_MODE_DYNAMIC : DUK_BUF_MODE_FIXED);
		if ((tmp == mode && !DUK_HBUFFER_HAS_EXTERNAL(h_buf)) ||
		    mode == DUK_BUF_MODE_DONTCARE) {
			/* Note: src_data may be NULL if input is a zero-size
			 * dynamic buffer.
			 */
			dst_data = tmp_ptr;
			goto skip_copy;
		}
	} else {
		/* Non-buffer value is first ToString() coerced, then converted
		 * to a buffer (fixed buffer is used unless a dynamic buffer is
		 * explicitly requested).  Symbols are rejected with a TypeError.
		 * XXX: C API could maybe allow symbol-to-buffer coercion?
		 */
		src_data = (const duk_uint8_t *) duk_to_lstring(thr, idx, &src_size);
	}

	dst_data = (duk_uint8_t *) duk_push_buffer(thr, src_size, (mode == DUK_BUF_MODE_DYNAMIC) /*dynamic*/);
	/* dst_data may be NULL if size is zero. */
	duk_memcpy_unsafe((void *) dst_data, (const void *) src_data, (size_t) src_size);

	duk_replace(thr, idx);
 skip_copy:

	if (out_size) {
		*out_size = src_size;
	}
	return dst_data;
}

DUK_EXTERNAL void *duk_to_pointer(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	void *res;

	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);
	tv = DUK_GET_TVAL_POSIDX(thr, idx);
	DUK_ASSERT(tv != NULL);

	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_UNDEFINED:
	case DUK_TAG_NULL:
	case DUK_TAG_BOOLEAN:
		res = NULL;
		break;
	case DUK_TAG_POINTER:
		res = DUK_TVAL_GET_POINTER(tv);
		break;
	case DUK_TAG_STRING:
	case DUK_TAG_OBJECT:
	case DUK_TAG_BUFFER:
		/* Heap allocated: return heap pointer which is NOT useful
		 * for the caller, except for debugging.
		 */
		res = (void *) DUK_TVAL_GET_HEAPHDR(tv);
		break;
	case DUK_TAG_LIGHTFUNC:
		/* Function pointers do not always cast correctly to void *
		 * (depends on memory and segmentation model for instance),
		 * so they coerce to NULL.
		 */
		res = NULL;
		break;
#if defined(DUK_USE_FASTINT)
	case DUK_TAG_FASTINT:
#endif
	default:
		/* number */
		DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
		DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv));
		res = NULL;
		break;
	}

	duk_push_pointer(thr, res);
	duk_replace(thr, idx);
	return res;
}

DUK_LOCAL void duk__push_func_from_lightfunc(duk_hthread *thr, duk_c_function func, duk_small_uint_t lf_flags) {
	duk_idx_t nargs;
	duk_uint_t flags = 0;   /* shared flags for a subset of types */
	duk_small_uint_t lf_len;
	duk_hnatfunc *nf;

	nargs = (duk_idx_t) DUK_LFUNC_FLAGS_GET_NARGS(lf_flags);
	if (nargs == DUK_LFUNC_NARGS_VARARGS) {
		nargs = (duk_idx_t) DUK_VARARGS;
	}

	flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
	        DUK_HOBJECT_FLAG_CONSTRUCTABLE |
	        DUK_HOBJECT_FLAG_CALLABLE |
	        DUK_HOBJECT_FLAG_FASTREFS |
	        DUK_HOBJECT_FLAG_NATFUNC |
	        DUK_HOBJECT_FLAG_NEWENV |
	        DUK_HOBJECT_FLAG_STRICT |
	        DUK_HOBJECT_FLAG_NOTAIL |
	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);
	(void) duk__push_c_function_raw(thr, func, nargs, flags, DUK_BIDX_NATIVE_FUNCTION_PROTOTYPE);

	lf_len = DUK_LFUNC_FLAGS_GET_LENGTH(lf_flags);
	if ((duk_idx_t) lf_len != nargs) {
		/* Explicit length is only needed if it differs from 'nargs'. */
		duk_push_int(thr, (duk_int_t) lf_len);
		duk_xdef_prop_stridx_short(thr, -2, DUK_STRIDX_LENGTH, DUK_PROPDESC_FLAGS_NONE);
	}

#if defined(DUK_USE_FUNC_NAME_PROPERTY)
	duk_push_lightfunc_name_raw(thr, func, lf_flags);
	duk_xdef_prop_stridx_short(thr, -2, DUK_STRIDX_NAME, DUK_PROPDESC_FLAGS_C);
#endif

	nf = duk_known_hnatfunc(thr, -1);
	nf->magic = (duk_int16_t) DUK_LFUNC_FLAGS_GET_MAGIC(lf_flags);
}

DUK_EXTERNAL void duk_to_object(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_uint_t flags = 0;   /* shared flags for a subset of types */
	duk_small_int_t proto = 0;

	DUK_ASSERT_API_ENTRY(thr);

	idx = duk_require_normalize_index(thr, idx);
	tv = DUK_GET_TVAL_POSIDX(thr, idx);
	DUK_ASSERT(tv != NULL);

	switch (DUK_TVAL_GET_TAG(tv)) {
#if !defined(DUK_USE_BUFFEROBJECT_SUPPORT)
	case DUK_TAG_BUFFER:  /* With no bufferobject support, don't object coerce. */
#endif
	case DUK_TAG_UNDEFINED:
	case DUK_TAG_NULL: {
		DUK_ERROR_TYPE(thr, DUK_STR_NOT_OBJECT_COERCIBLE);
		DUK_WO_NORETURN(return;);
		break;
	}
	case DUK_TAG_BOOLEAN: {
		flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
		        DUK_HOBJECT_FLAG_FASTREFS |
		        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_BOOLEAN);
		proto = DUK_BIDX_BOOLEAN_PROTOTYPE;
		goto create_object;
	}
	case DUK_TAG_STRING: {
		duk_hstring *h;
		h = DUK_TVAL_GET_STRING(tv);
		DUK_ASSERT(h != NULL);
		if (DUK_UNLIKELY(DUK_HSTRING_HAS_SYMBOL(h))) {
			flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
			        DUK_HOBJECT_FLAG_FASTREFS |
			        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_SYMBOL);
			proto = DUK_BIDX_SYMBOL_PROTOTYPE;
		} else {
			flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
			        DUK_HOBJECT_FLAG_FASTREFS |
			        DUK_HOBJECT_FLAG_EXOTIC_STRINGOBJ |
			        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_STRING);
			proto = DUK_BIDX_STRING_PROTOTYPE;
		}
		goto create_object;
	}
	case DUK_TAG_OBJECT: {
		/* nop */
		break;
	}
#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
	case DUK_TAG_BUFFER: {
		/* A plain buffer object coerces to a full ArrayBuffer which
		 * is not fully transparent behavior (ToObject() should be a
		 * nop for an object).  This behavior matches lightfuncs which
		 * also coerce to an equivalent Function object.  There are
		 * also downsides to defining ToObject(plainBuffer) as a no-op;
		 * for example duk_to_hobject() could result in a NULL pointer.
		 */
		duk_hbuffer *h_buf;

		h_buf = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h_buf != NULL);
		duk_hbufobj_push_uint8array_from_plain(thr, h_buf);
		goto replace_value;
	}
#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */
	case DUK_TAG_POINTER: {
		flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
		        DUK_HOBJECT_FLAG_FASTREFS |
		        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_POINTER);
		proto = DUK_BIDX_POINTER_PROTOTYPE;
		goto create_object;
	}
	case DUK_TAG_LIGHTFUNC: {
		/* Lightfunc coerces to a Function instance with concrete
		 * properties.  Since 'length' is virtual for Duktape/C
		 * functions, don't need to define that.  The result is made
		 * extensible to mimic what happens to strings in object
		 * coercion:
		 *
		 *   > Object.isExtensible(Object('foo'))
		 *   true
		 */
		duk_small_uint_t lf_flags;
		duk_c_function func;

		DUK_TVAL_GET_LIGHTFUNC(tv, func, lf_flags);
		duk__push_func_from_lightfunc(thr, func, lf_flags);
		goto replace_value;
	}
#if defined(DUK_USE_FASTINT)
	case DUK_TAG_FASTINT:
#endif
	default: {
		DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
		DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv));
		flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
		        DUK_HOBJECT_FLAG_FASTREFS |
		        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_NUMBER);
		proto = DUK_BIDX_NUMBER_PROTOTYPE;
		goto create_object;
	}
	}
	DUK_ASSERT(duk_is_object(thr, idx));
	return;

 create_object:
	(void) duk_push_object_helper(thr, flags, proto);

	/* Note: Boolean prototype's internal value property is not writable,
	 * but duk_xdef_prop_stridx() disregards the write protection.  Boolean
	 * instances are immutable.
	 *
	 * String and buffer special behaviors are already enabled which is not
	 * ideal, but a write to the internal value is not affected by them.
	 */
	duk_dup(thr, idx);
	duk_xdef_prop_stridx_short(thr, -2, DUK_STRIDX_INT_VALUE, DUK_PROPDESC_FLAGS_NONE);

 replace_value:
	duk_replace(thr, idx);
	DUK_ASSERT(duk_is_object(thr, idx));
}

DUK_INTERNAL duk_hobject *duk_to_hobject(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *ret;

	DUK_ASSERT_API_ENTRY(thr);

	duk_to_object(thr, idx);
	ret = duk_known_hobject(thr, idx);
	return ret;
}

/*
 *  Type checking
 */

DUK_LOCAL duk_bool_t duk__tag_check(duk_hthread *thr, duk_idx_t idx, duk_small_uint_t tag) {
	duk_tval *tv;

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	return (DUK_TVAL_GET_TAG(tv) == tag);
}

DUK_LOCAL duk_bool_t duk__obj_flag_any_default_false(duk_hthread *thr, duk_idx_t idx, duk_uint_t flag_mask) {
	duk_hobject *obj;

	DUK_ASSERT_API_ENTRY(thr);

	obj = duk_get_hobject(thr, idx);
	if (obj) {
		return (DUK_HEAPHDR_CHECK_FLAG_BITS((duk_heaphdr *) obj, flag_mask) ? 1 : 0);
	}
	return 0;
}

DUK_INTERNAL duk_int_t duk_get_type_tval(duk_tval *tv) {
	DUK_ASSERT(tv != NULL);

#if defined(DUK_USE_PACKED_TVAL)
	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_UNUSED:
		return DUK_TYPE_NONE;
	case DUK_TAG_UNDEFINED:
		return DUK_TYPE_UNDEFINED;
	case DUK_TAG_NULL:
		return DUK_TYPE_NULL;
	case DUK_TAG_BOOLEAN:
		return DUK_TYPE_BOOLEAN;
	case DUK_TAG_STRING:
		return DUK_TYPE_STRING;
	case DUK_TAG_OBJECT:
		return DUK_TYPE_OBJECT;
	case DUK_TAG_BUFFER:
		return DUK_TYPE_BUFFER;
	case DUK_TAG_POINTER:
		return DUK_TYPE_POINTER;
	case DUK_TAG_LIGHTFUNC:
		return DUK_TYPE_LIGHTFUNC;
#if defined(DUK_USE_FASTINT)
	case DUK_TAG_FASTINT:
#endif
	default:
		/* Note: number has no explicit tag (in 8-byte representation) */
		DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
		DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv));
		return DUK_TYPE_NUMBER;
	}
#else  /* DUK_USE_PACKED_TVAL */
	DUK_ASSERT(DUK_TVAL_IS_VALID_TAG(tv));
	DUK_ASSERT(sizeof(duk__type_from_tag) / sizeof(duk_uint_t) == DUK_TAG_MAX - DUK_TAG_MIN + 1);
	return (duk_int_t) duk__type_from_tag[DUK_TVAL_GET_TAG(tv) - DUK_TAG_MIN];
#endif  /* DUK_USE_PACKED_TVAL */
}

DUK_EXTERNAL duk_int_t duk_get_type(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	return duk_get_type_tval(tv);
}

#if defined(DUK_USE_VERBOSE_ERRORS) && defined(DUK_USE_PARANOID_ERRORS)
DUK_LOCAL const char * const duk__type_names[] = {
	"none",
	"undefined",
	"null",
	"boolean",
	"number",
	"string",
	"object",
	"buffer",
	"pointer",
	"lightfunc"
};

DUK_INTERNAL const char *duk_get_type_name(duk_hthread *thr, duk_idx_t idx) {
	duk_int_t type_tag;

	DUK_ASSERT_API_ENTRY(thr);

	type_tag = duk_get_type(thr, idx);
	DUK_ASSERT(type_tag >= DUK_TYPE_MIN && type_tag <= DUK_TYPE_MAX);
	DUK_ASSERT(DUK_TYPE_MIN == 0 && sizeof(duk__type_names) / sizeof(const char *) == DUK_TYPE_MAX + 1);

	return duk__type_names[type_tag];
}
#endif  /* DUK_USE_VERBOSE_ERRORS && DUK_USE_PARANOID_ERRORS */

DUK_INTERNAL duk_small_uint_t duk_get_class_number(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;
	duk_hobject *obj;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_OBJECT:
		obj = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(obj != NULL);
		return DUK_HOBJECT_GET_CLASS_NUMBER(obj);
	case DUK_TAG_BUFFER:
		/* Buffers behave like Uint8Array objects. */
		return DUK_HOBJECT_CLASS_UINT8ARRAY;
	case DUK_TAG_LIGHTFUNC:
		/* Lightfuncs behave like Function objects. */
		return DUK_HOBJECT_CLASS_FUNCTION;
	default:
		/* Primitive or UNUSED, no class number. */
		return DUK_HOBJECT_CLASS_NONE;
	}
}

DUK_EXTERNAL duk_bool_t duk_check_type(duk_hthread *thr, duk_idx_t idx, duk_int_t type) {
	DUK_ASSERT_API_ENTRY(thr);

	return (duk_get_type(thr, idx) == type) ? 1 : 0;
}

DUK_INTERNAL duk_uint_t duk_get_type_mask_tval(duk_tval *tv) {
	DUK_ASSERT(tv != NULL);

#if defined(DUK_USE_PACKED_TVAL)
	switch (DUK_TVAL_GET_TAG(tv)) {
	case DUK_TAG_UNUSED:
		return DUK_TYPE_MASK_NONE;
	case DUK_TAG_UNDEFINED:
		return DUK_TYPE_MASK_UNDEFINED;
	case DUK_TAG_NULL:
		return DUK_TYPE_MASK_NULL;
	case DUK_TAG_BOOLEAN:
		return DUK_TYPE_MASK_BOOLEAN;
	case DUK_TAG_STRING:
		return DUK_TYPE_MASK_STRING;
	case DUK_TAG_OBJECT:
		return DUK_TYPE_MASK_OBJECT;
	case DUK_TAG_BUFFER:
		return DUK_TYPE_MASK_BUFFER;
	case DUK_TAG_POINTER:
		return DUK_TYPE_MASK_POINTER;
	case DUK_TAG_LIGHTFUNC:
		return DUK_TYPE_MASK_LIGHTFUNC;
#if defined(DUK_USE_FASTINT)
	case DUK_TAG_FASTINT:
#endif
	default:
		/* Note: number has no explicit tag (in 8-byte representation) */
		DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
		DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv));
		return DUK_TYPE_MASK_NUMBER;
	}
#else  /* DUK_USE_PACKED_TVAL */
	DUK_ASSERT(DUK_TVAL_IS_VALID_TAG(tv));
	DUK_ASSERT(sizeof(duk__type_mask_from_tag) / sizeof(duk_uint_t) == DUK_TAG_MAX - DUK_TAG_MIN + 1);
	return duk__type_mask_from_tag[DUK_TVAL_GET_TAG(tv) - DUK_TAG_MIN];
#endif  /* DUK_USE_PACKED_TVAL */
}

DUK_EXTERNAL duk_uint_t duk_get_type_mask(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	return duk_get_type_mask_tval(tv);
}

DUK_EXTERNAL duk_bool_t duk_check_type_mask(duk_hthread *thr, duk_idx_t idx, duk_uint_t mask) {
	DUK_ASSERT_API_ENTRY(thr);

	if (DUK_LIKELY((duk_get_type_mask(thr, idx) & mask) != 0U)) {
		return 1;
	}
	if (mask & DUK_TYPE_MASK_THROW) {
		DUK_ERROR_TYPE(thr, DUK_STR_UNEXPECTED_TYPE);
		DUK_WO_NORETURN(return 0;);
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_undefined(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_UNDEFINED);
}

DUK_EXTERNAL duk_bool_t duk_is_null(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_NULL);
}

DUK_EXTERNAL duk_bool_t duk_is_boolean(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_BOOLEAN);
}

DUK_EXTERNAL duk_bool_t duk_is_number(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	/*
	 *  Number is special because it doesn't have a specific
	 *  tag in the 8-byte representation.
	 */

	/* XXX: shorter version for unpacked representation? */

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	return DUK_TVAL_IS_NUMBER(tv);
}

DUK_EXTERNAL duk_bool_t duk_is_nan(duk_hthread *thr, duk_idx_t idx) {
	/* XXX: This will now return false for non-numbers, even though they would
	 * coerce to NaN (as a general rule).  In particular, duk_get_number()
	 * returns a NaN for non-numbers, so should this function also return
	 * true for non-numbers?
	 */

	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);

	/* XXX: for packed duk_tval an explicit "is number" check is unnecessary */
	if (!DUK_TVAL_IS_NUMBER(tv)) {
		return 0;
	}
	return (duk_bool_t) DUK_ISNAN(DUK_TVAL_GET_NUMBER(tv));
}

DUK_EXTERNAL duk_bool_t duk_is_string(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_STRING);
}

DUK_INTERNAL duk_bool_t duk_is_string_notsymbol(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_get_hstring_notsymbol(thr, idx) != NULL;
}

DUK_EXTERNAL duk_bool_t duk_is_object(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_OBJECT);
}

DUK_EXTERNAL duk_bool_t duk_is_buffer(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_BUFFER);
}

#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
DUK_EXTERNAL duk_bool_t duk_is_buffer_data(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_TVAL_IS_BUFFER(tv)) {
		return 1;
	} else if (DUK_TVAL_IS_OBJECT(tv)) {
		duk_hobject *h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		if (DUK_HOBJECT_IS_BUFOBJ(h)) {
			return 1;
		}
	}
	return 0;
}
#else  /* DUK_USE_BUFFEROBJECT_SUPPORT */
DUK_EXTERNAL duk_bool_t duk_is_buffer_data(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);

	return duk_is_buffer(thr, idx);
}

#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */

DUK_EXTERNAL duk_bool_t duk_is_pointer(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_POINTER);
}

DUK_EXTERNAL duk_bool_t duk_is_lightfunc(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__tag_check(thr, idx, DUK_TAG_LIGHTFUNC);
}

DUK_EXTERNAL duk_bool_t duk_is_symbol(duk_hthread *thr, duk_idx_t idx) {
	duk_hstring *h;

	DUK_ASSERT_API_ENTRY(thr);
	h = duk_get_hstring(thr, idx);
	/* Use DUK_LIKELY() here because caller may be more likely to type
	 * check an expected symbol than not.
	 */
	if (DUK_LIKELY(h != NULL && DUK_HSTRING_HAS_SYMBOL(h))) {
		return 1;
	}
	return 0;
}

/* IsArray(), returns true for Array instance or Proxy of Array instance. */
DUK_EXTERNAL duk_bool_t duk_is_array(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval(thr, idx);
	if (tv) {
		return duk_js_isarray(tv);
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_function(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	if (DUK_TVAL_IS_OBJECT(tv)) {
		duk_hobject *h;
		h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		return DUK_HOBJECT_HAS_CALLABLE(h) ? 1 : 0;
	}
	if (DUK_TVAL_IS_LIGHTFUNC(tv)) {
		return 1;
	}
	return 0;
}

DUK_INTERNAL duk_bool_t duk_is_callable_tval(duk_hthread *thr, duk_tval *tv) {
	DUK_ASSERT_API_ENTRY(thr);

	DUK_UNREF(thr);

	if (DUK_TVAL_IS_OBJECT(tv)) {
		duk_hobject *h;
		h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		return DUK_HOBJECT_HAS_CALLABLE(h) ? 1 : 0;
	}
	if (DUK_TVAL_IS_LIGHTFUNC(tv)) {
		return 1;
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_constructable(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	if (DUK_TVAL_IS_OBJECT(tv)) {
		duk_hobject *h;
		h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		return DUK_HOBJECT_HAS_CONSTRUCTABLE(h) ? 1 : 0;
	}
	if (DUK_TVAL_IS_LIGHTFUNC(tv)) {
		return 1;
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_c_function(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__obj_flag_any_default_false(thr,
	                                       idx,
	                                       DUK_HOBJECT_FLAG_NATFUNC);
}

DUK_EXTERNAL duk_bool_t duk_is_ecmascript_function(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__obj_flag_any_default_false(thr,
	                                       idx,
	                                       DUK_HOBJECT_FLAG_COMPFUNC);
}

DUK_EXTERNAL duk_bool_t duk_is_bound_function(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__obj_flag_any_default_false(thr,
	                                       idx,
	                                       DUK_HOBJECT_FLAG_BOUNDFUNC);
}

DUK_EXTERNAL duk_bool_t duk_is_thread(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *obj;

	DUK_ASSERT_API_ENTRY(thr);

	obj = duk_get_hobject(thr, idx);
	if (obj) {
		return (DUK_HOBJECT_GET_CLASS_NUMBER(obj) == DUK_HOBJECT_CLASS_THREAD ? 1 : 0);
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_fixed_buffer(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_TVAL_IS_BUFFER(tv)) {
		duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h != NULL);
		return (DUK_HBUFFER_HAS_DYNAMIC(h) ? 0 : 1);
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_dynamic_buffer(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_TVAL_IS_BUFFER(tv)) {
		duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h != NULL);
		return (DUK_HBUFFER_HAS_DYNAMIC(h) && !DUK_HBUFFER_HAS_EXTERNAL(h) ? 1 : 0);
	}
	return 0;
}

DUK_EXTERNAL duk_bool_t duk_is_external_buffer(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_get_tval_or_unused(thr, idx);
	DUK_ASSERT(tv != NULL);
	if (DUK_TVAL_IS_BUFFER(tv)) {
		duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
		DUK_ASSERT(h != NULL);
		return (DUK_HBUFFER_HAS_DYNAMIC(h) && DUK_HBUFFER_HAS_EXTERNAL(h) ? 1 : 0);
	}
	return 0;
}

DUK_EXTERNAL duk_errcode_t duk_get_error_code(duk_hthread *thr, duk_idx_t idx) {
	duk_hobject *h;
	duk_uint_t sanity;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_get_hobject(thr, idx);

	sanity = DUK_HOBJECT_PROTOTYPE_CHAIN_SANITY;
	do {
		if (!h) {
			return DUK_ERR_NONE;
		}

		/* XXX: something more convenient? */

		if (h == thr->builtins[DUK_BIDX_EVAL_ERROR_PROTOTYPE]) {
			return DUK_ERR_EVAL_ERROR;
		}
		if (h == thr->builtins[DUK_BIDX_RANGE_ERROR_PROTOTYPE]) {
			return DUK_ERR_RANGE_ERROR;
		}
		if (h == thr->builtins[DUK_BIDX_REFERENCE_ERROR_PROTOTYPE]) {
			return DUK_ERR_REFERENCE_ERROR;
		}
		if (h == thr->builtins[DUK_BIDX_SYNTAX_ERROR_PROTOTYPE]) {
			return DUK_ERR_SYNTAX_ERROR;
		}
		if (h == thr->builtins[DUK_BIDX_TYPE_ERROR_PROTOTYPE]) {
			return DUK_ERR_TYPE_ERROR;
		}
		if (h == thr->builtins[DUK_BIDX_URI_ERROR_PROTOTYPE]) {
			return DUK_ERR_URI_ERROR;
		}
		if (h == thr->builtins[DUK_BIDX_ERROR_PROTOTYPE]) {
			return DUK_ERR_ERROR;
		}

		h = DUK_HOBJECT_GET_PROTOTYPE(thr->heap, h);
	} while (--sanity > 0);

	return DUK_ERR_NONE;
}

/*
 *  Pushers
 */

DUK_INTERNAL void duk_push_tval(duk_hthread *thr, duk_tval *tv) {
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(tv != NULL);

	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_TVAL(tv_slot, tv);
	DUK_TVAL_INCREF(thr, tv);  /* no side effects */
}

DUK_EXTERNAL void duk_push_undefined(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	DUK__CHECK_SPACE();

	/* Because value stack init policy is 'undefined above top',
	 * we don't need to write, just assert.
	 */
	thr->valstack_top++;
	DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(thr->valstack_top - 1));
}

DUK_EXTERNAL void duk_push_null(duk_hthread *thr) {
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_NULL(tv_slot);
}

DUK_EXTERNAL void duk_push_boolean(duk_hthread *thr, duk_bool_t val) {
	duk_tval *tv_slot;
	duk_small_int_t b;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	b = (val ? 1 : 0);  /* ensure value is 1 or 0 (not other non-zero) */
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_BOOLEAN(tv_slot, b);
}

DUK_EXTERNAL void duk_push_true(duk_hthread *thr) {
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_BOOLEAN_TRUE(tv_slot);
}

DUK_EXTERNAL void duk_push_false(duk_hthread *thr) {
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_BOOLEAN_FALSE(tv_slot);
}

/* normalize NaN which may not match our canonical internal NaN */
DUK_EXTERNAL void duk_push_number(duk_hthread *thr, duk_double_t val) {
	duk_tval *tv_slot;
	duk_double_union du;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	du.d = val;
	DUK_DBLUNION_NORMALIZE_NAN_CHECK(&du);
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_NUMBER(tv_slot, du.d);
}

DUK_EXTERNAL void duk_push_int(duk_hthread *thr, duk_int_t val) {
#if defined(DUK_USE_FASTINT)
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
#if DUK_INT_MAX <= 0x7fffffffL
	DUK_TVAL_SET_I32(tv_slot, (duk_int32_t) val);
#else
	if (val >= DUK_FASTINT_MIN && val <= DUK_FASTINT_MAX) {
		DUK_TVAL_SET_FASTINT(tv_slot, (duk_int64_t) val);
	} else {
		duk_double_t = (duk_double_t) val;
		DUK_TVAL_SET_NUMBER(tv_slot, d);
	}
#endif
#else  /* DUK_USE_FASTINT */
	duk_tval *tv_slot;
	duk_double_t d;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	d = (duk_double_t) val;
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_NUMBER(tv_slot, d);
#endif  /* DUK_USE_FASTINT */
}

DUK_EXTERNAL void duk_push_uint(duk_hthread *thr, duk_uint_t val) {
#if defined(DUK_USE_FASTINT)
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
#if DUK_UINT_MAX <= 0xffffffffUL
	DUK_TVAL_SET_U32(tv_slot, (duk_uint32_t) val);
#else
	if (val <= DUK_FASTINT_MAX) {  /* val is unsigned so >= 0 */
		/* XXX: take advantage of val being unsigned, no need to mask */
		DUK_TVAL_SET_FASTINT(tv_slot, (duk_int64_t) val);
	} else {
		duk_double_t = (duk_double_t) val;
		DUK_TVAL_SET_NUMBER(tv_slot, d);
	}
#endif
#else  /* DUK_USE_FASTINT */
	duk_tval *tv_slot;
	duk_double_t d;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	d = (duk_double_t) val;
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_NUMBER(tv_slot, d);
#endif  /* DUK_USE_FASTINT */
}

DUK_EXTERNAL void duk_push_nan(duk_hthread *thr) {
	duk_tval *tv_slot;
	duk_double_union du;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	DUK_DBLUNION_SET_NAN(&du);
	DUK_ASSERT(DUK_DBLUNION_IS_NORMALIZED(&du));
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_NUMBER(tv_slot, du.d);
}

DUK_EXTERNAL const char *duk_push_lstring(duk_hthread *thr, const char *str, duk_size_t len) {
	duk_hstring *h;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	/* Check stack before interning (avoid hanging temp). */
	DUK__CHECK_SPACE();

	/* NULL with zero length represents an empty string; NULL with higher
	 * length is also now treated like an empty string although it is
	 * a bit dubious.  This is unlike duk_push_string() which pushes a
	 * 'null' if the input string is a NULL.
	 */
	if (DUK_UNLIKELY(str == NULL)) {
		len = 0U;
	}

	/* Check for maximum string length. */
	if (DUK_UNLIKELY(len > DUK_HSTRING_MAX_BYTELEN)) {
		DUK_ERROR_RANGE(thr, DUK_STR_STRING_TOO_LONG);
		DUK_WO_NORETURN(return NULL;);
	}

	h = duk_heap_strtable_intern_checked(thr, (const duk_uint8_t *) str, (duk_uint32_t) len);
	DUK_ASSERT(h != NULL);

	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_STRING(tv_slot, h);
	DUK_HSTRING_INCREF(thr, h);  /* no side effects */

	return (const char *) DUK_HSTRING_GET_DATA(h);
}

DUK_EXTERNAL const char *duk_push_string(duk_hthread *thr, const char *str) {
	DUK_ASSERT_API_ENTRY(thr);

	if (str) {
		return duk_push_lstring(thr, str, DUK_STRLEN(str));
	} else {
		duk_push_null(thr);
		return NULL;
	}
}

#if !defined(DUK_USE_PREFER_SIZE)
#if defined(DUK_USE_LITCACHE_SIZE)
DUK_EXTERNAL const char *duk_push_literal_raw(duk_hthread *thr, const char *str, duk_size_t len) {
	duk_hstring *h;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(str != NULL);
	DUK_ASSERT(str[len] == (char) 0);

	/* Check for maximum string length. */
	if (DUK_UNLIKELY(len > DUK_HSTRING_MAX_BYTELEN)) {
		DUK_ERROR_RANGE(thr, DUK_STR_STRING_TOO_LONG);
		DUK_WO_NORETURN(return NULL;);
	}

	h = duk_heap_strtable_intern_literal_checked(thr, (const duk_uint8_t *) str, (duk_uint32_t) len);
	DUK_ASSERT(h != NULL);

	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_STRING(tv_slot, h);
	DUK_HSTRING_INCREF(thr, h);  /* no side effects */

	return (const char *) DUK_HSTRING_GET_DATA(h);
}
#else  /* DUK_USE_LITCACHE_SIZE */
DUK_EXTERNAL const char *duk_push_literal_raw(duk_hthread *thr, const char *str, duk_size_t len) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(str != NULL);
	DUK_ASSERT(str[len] == (char) 0);

	return duk_push_lstring(thr, str, len);
}
#endif  /* DUK_USE_LITCACHE_SIZE */
#endif  /* !DUK_USE_PREFER_SIZE */

DUK_EXTERNAL void duk_push_pointer(duk_hthread *thr, void *val) {
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK__CHECK_SPACE();
	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_POINTER(tv_slot, val);
}

DUK_INTERNAL duk_hstring *duk_push_uint_to_hstring(duk_hthread *thr, duk_uint_t i) {
	duk_hstring *h_tmp;

	DUK_ASSERT_API_ENTRY(thr);

	/* XXX: this could be a direct DUK_SPRINTF to a buffer followed by duk_push_string() */
	duk_push_uint(thr, (duk_uint_t) i);
	h_tmp = duk_to_hstring_m1(thr);
	DUK_ASSERT(h_tmp != NULL);
	return h_tmp;
}

DUK_LOCAL void duk__push_this_helper(duk_hthread *thr, duk_small_uint_t check_object_coercible) {
	duk_tval *tv_slot;

	DUK__CHECK_SPACE();

	DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(thr->valstack_top));  /* because of valstack init policy */
	tv_slot = thr->valstack_top++;

	if (DUK_UNLIKELY(thr->callstack_curr == NULL)) {
		if (check_object_coercible) {
			goto type_error;
		}
		/* 'undefined' already on stack top */
	} else {
		duk_tval *tv;

		/* 'this' binding is just before current activation's bottom */
		DUK_ASSERT(thr->valstack_bottom > thr->valstack);
		tv = thr->valstack_bottom - 1;
		if (check_object_coercible &&
		    (DUK_TVAL_IS_UNDEFINED(tv) || DUK_TVAL_IS_NULL(tv))) {
			/* XXX: better macro for DUK_TVAL_IS_UNDEFINED_OR_NULL(tv) */
			goto type_error;
		}

		DUK_TVAL_SET_TVAL(tv_slot, tv);
		DUK_TVAL_INCREF(thr, tv);
	}
	return;

 type_error:
	DUK_ERROR_TYPE(thr, DUK_STR_NOT_OBJECT_COERCIBLE);
	DUK_WO_NORETURN(return;);
}

DUK_EXTERNAL void duk_push_this(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	duk__push_this_helper(thr, 0 /*check_object_coercible*/);
}

DUK_INTERNAL void duk_push_this_check_object_coercible(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	duk__push_this_helper(thr, 1 /*check_object_coercible*/);
}

DUK_INTERNAL duk_hobject *duk_push_this_coercible_to_object(duk_hthread *thr) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	duk__push_this_helper(thr, 1 /*check_object_coercible*/);
	h = duk_to_hobject(thr, -1);
	DUK_ASSERT(h != NULL);
	return h;
}

DUK_INTERNAL duk_hstring *duk_push_this_coercible_to_string(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	duk__push_this_helper(thr, 1 /*check_object_coercible*/);
	return duk_to_hstring_m1(thr);  /* This will reject all Symbol values; accepts Symbol objects. */
}

DUK_INTERNAL duk_tval *duk_get_borrowed_this_tval(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	DUK_ASSERT(thr->callstack_top > 0);  /* caller required to know */
	DUK_ASSERT(thr->callstack_curr != NULL);  /* caller required to know */
	DUK_ASSERT(thr->valstack_bottom > thr->valstack);  /* consequence of above */
	DUK_ASSERT(thr->valstack_bottom - 1 >= thr->valstack);  /* 'this' binding exists */

	return thr->valstack_bottom - 1;
}

DUK_EXTERNAL void duk_push_new_target(duk_hthread *thr) {
	duk_activation *act;

	DUK_ASSERT_API_ENTRY(thr);

	/* https://www.ecma-international.org/ecma-262/6.0/#sec-meta-properties-runtime-semantics-evaluation
	 * https://www.ecma-international.org/ecma-262/6.0/#sec-getnewtarget
	 *
	 * No newTarget support now, so as a first approximation
	 * use the resolved (non-bound) target function.
	 *
	 * Check CONSTRUCT flag from current function, or if running
	 * direct eval, from a non-direct-eval parent (with possibly
	 * more than one nested direct eval).  An alternative to this
	 * would be to store [[NewTarget]] as a hidden symbol of the
	 * lexical scope, and then just look up that variable.
	 *
	 * Calls from the application will either be for an empty
	 * call stack, or a Duktape/C function as the top activation.
	 */

	act = thr->callstack_curr;
	for (;;) {
		if (act == NULL) {
			break;
		}

		if (act->flags & DUK_ACT_FLAG_CONSTRUCT) {
			duk_push_tval(thr, &act->tv_func);
			return;
		} else if (act->flags & DUK_ACT_FLAG_DIRECT_EVAL) {
			act = act->parent;
		} else {
			break;
		}
	}

	duk_push_undefined(thr);
}

DUK_EXTERNAL void duk_push_current_function(duk_hthread *thr) {
	duk_activation *act;

	DUK_ASSERT_API_ENTRY(thr);

	act = thr->callstack_curr;
	if (act != NULL) {
		duk_push_tval(thr, &act->tv_func);
	} else {
		duk_push_undefined(thr);
	}
}

DUK_EXTERNAL void duk_push_current_thread(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	if (thr->heap->curr_thread) {
		duk_push_hobject(thr, (duk_hobject *) thr->heap->curr_thread);
	} else {
		duk_push_undefined(thr);
	}
}

DUK_EXTERNAL void duk_push_global_object(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_push_hobject_bidx(thr, DUK_BIDX_GLOBAL);
}

/* XXX: size optimize */
DUK_LOCAL void duk__push_stash(duk_hthread *thr) {
	if (!duk_xget_owndataprop_stridx_short(thr, -1, DUK_STRIDX_INT_VALUE)) {
		DUK_DDD(DUK_DDDPRINT("creating heap/global/thread stash on first use"));
		duk_pop_unsafe(thr);
		duk_push_bare_object(thr);
		duk_dup_top(thr);
		duk_xdef_prop_stridx_short(thr, -3, DUK_STRIDX_INT_VALUE, DUK_PROPDESC_FLAGS_C);  /* [ ... parent stash stash ] -> [ ... parent stash ] */
	}
	duk_remove_m2(thr);
}

DUK_EXTERNAL void duk_push_heap_stash(duk_hthread *thr) {
	duk_heap *heap;
	DUK_ASSERT_API_ENTRY(thr);
	heap = thr->heap;
	DUK_ASSERT(heap->heap_object != NULL);
	duk_push_hobject(thr, heap->heap_object);
	duk__push_stash(thr);
}

DUK_EXTERNAL void duk_push_global_stash(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_push_global_object(thr);
	duk__push_stash(thr);
}

DUK_EXTERNAL void duk_push_thread_stash(duk_hthread *thr, duk_hthread *target_thr) {
	DUK_ASSERT_API_ENTRY(thr);
	if (DUK_UNLIKELY(target_thr == NULL)) {
		DUK_ERROR_TYPE_INVALID_ARGS(thr);
		DUK_WO_NORETURN(return;);
	}
	duk_push_hobject(thr, (duk_hobject *) target_thr);
	duk__push_stash(thr);
}

/* XXX: duk_ssize_t would be useful here */
DUK_LOCAL duk_int_t duk__try_push_vsprintf(duk_hthread *thr, void *buf, duk_size_t sz, const char *fmt, va_list ap) {
	duk_int_t len;

	DUK_CTX_ASSERT_VALID(thr);
	DUK_UNREF(thr);

	/* NUL terminator handling doesn't matter here */
	len = DUK_VSNPRINTF((char *) buf, sz, fmt, ap);
	if (len < (duk_int_t) sz) {
		/* Return value of 'sz' or more indicates output was (potentially)
		 * truncated.
		 */
		return (duk_int_t) len;
	}
	return -1;
}

DUK_EXTERNAL const char *duk_push_vsprintf(duk_hthread *thr, const char *fmt, va_list ap) {
	duk_uint8_t stack_buf[DUK_PUSH_SPRINTF_INITIAL_SIZE];
	duk_size_t sz = DUK_PUSH_SPRINTF_INITIAL_SIZE;
	duk_bool_t pushed_buf = 0;
	void *buf;
	duk_int_t len;  /* XXX: duk_ssize_t */
	const char *res;

	DUK_ASSERT_API_ENTRY(thr);

	/* special handling of fmt==NULL */
	if (!fmt) {
		duk_hstring *h_str;
		duk_push_hstring_empty(thr);
		h_str = duk_known_hstring(thr, -1);
		return (const char *) DUK_HSTRING_GET_DATA(h_str);
	}

	/* initial estimate based on format string */
	sz = DUK_STRLEN(fmt) + 16;  /* format plus something to avoid just missing */
	if (sz < DUK_PUSH_SPRINTF_INITIAL_SIZE) {
		sz = DUK_PUSH_SPRINTF_INITIAL_SIZE;
	}
	DUK_ASSERT(sz > 0);

	/* Try to make do with a stack buffer to avoid allocating a temporary buffer.
	 * This works 99% of the time which is quite nice.
	 */
	for (;;) {
		va_list ap_copy;  /* copied so that 'ap' can be reused */

		if (sz <= sizeof(stack_buf)) {
			buf = stack_buf;
		} else if (!pushed_buf) {
			pushed_buf = 1;
			buf = duk_push_dynamic_buffer(thr, sz);
		} else {
			buf = duk_resize_buffer(thr, -1, sz);
		}
		DUK_ASSERT(buf != NULL);

		DUK_VA_COPY(ap_copy, ap);
		len = duk__try_push_vsprintf(thr, buf, sz, fmt, ap_copy);
		va_end(ap_copy);
		if (len >= 0) {
			break;
		}

		/* failed, resize and try again */
		sz = sz * 2;
		if (DUK_UNLIKELY(sz >= DUK_PUSH_SPRINTF_SANITY_LIMIT)) {
			DUK_ERROR_RANGE(thr, DUK_STR_RESULT_TOO_LONG);
			DUK_WO_NORETURN(return NULL;);
		}
	}

	/* Cannot use duk_buffer_to_string() on the buffer because it is
	 * usually larger than 'len'; 'buf' is also usually a stack buffer.
	 */
	res = duk_push_lstring(thr, (const char *) buf, (duk_size_t) len);  /* [ buf? res ] */
	if (pushed_buf) {
		duk_remove_m2(thr);
	}
	return res;
}

DUK_EXTERNAL const char *duk_push_sprintf(duk_hthread *thr, const char *fmt, ...) {
	va_list ap;
	const char *ret;

	DUK_ASSERT_API_ENTRY(thr);

	/* allow fmt==NULL */
	va_start(ap, fmt);
	ret = duk_push_vsprintf(thr, fmt, ap);
	va_end(ap);

	return ret;
}

DUK_INTERNAL duk_hobject *duk_push_object_helper(duk_hthread *thr, duk_uint_t hobject_flags_and_class, duk_small_int_t prototype_bidx) {
	duk_tval *tv_slot;
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(prototype_bidx == -1 ||
	           (prototype_bidx >= 0 && prototype_bidx < DUK_NUM_BUILTINS));

	DUK__CHECK_SPACE();

	h = duk_hobject_alloc(thr, hobject_flags_and_class);
	DUK_ASSERT(h != NULL);

	DUK_DDD(DUK_DDDPRINT("created object with flags: 0x%08lx", (unsigned long) h->hdr.h_flags));

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, h);
	DUK_HOBJECT_INCREF(thr, h);  /* no side effects */
	thr->valstack_top++;

	/* object is now reachable */

	if (prototype_bidx >= 0) {
		DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, h, thr->builtins[prototype_bidx]);
	} else {
		DUK_ASSERT(prototype_bidx == -1);
		DUK_ASSERT(DUK_HOBJECT_GET_PROTOTYPE(thr->heap, h) == NULL);
	}

	return h;
}

DUK_INTERNAL duk_hobject *duk_push_object_helper_proto(duk_hthread *thr, duk_uint_t hobject_flags_and_class, duk_hobject *proto) {
	duk_hobject *h;

	DUK_ASSERT_API_ENTRY(thr);

	h = duk_push_object_helper(thr, hobject_flags_and_class, -1);
	DUK_ASSERT(h != NULL);
	DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, h, proto);
	return h;
}

DUK_EXTERNAL duk_idx_t duk_push_object(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	(void) duk_push_object_helper(thr,
	                              DUK_HOBJECT_FLAG_EXTENSIBLE |
	                              DUK_HOBJECT_FLAG_FASTREFS |
	                              DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_OBJECT),
	                              DUK_BIDX_OBJECT_PROTOTYPE);
	return duk_get_top_index_unsafe(thr);
}

DUK_EXTERNAL duk_idx_t duk_push_array(duk_hthread *thr) {
	duk_uint_t flags;
	duk_harray *obj;
	duk_idx_t ret;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
	        DUK_HOBJECT_FLAG_FASTREFS |
	        DUK_HOBJECT_FLAG_ARRAY_PART |
	        DUK_HOBJECT_FLAG_EXOTIC_ARRAY |
	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_ARRAY);

	obj = duk_harray_alloc(thr, flags);
	DUK_ASSERT(obj != NULL);

	DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, (duk_hobject *) obj, thr->builtins[DUK_BIDX_ARRAY_PROTOTYPE]);

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HOBJECT_INCREF(thr, obj);  /* XXX: could preallocate with refcount = 1 */
	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	thr->valstack_top++;

	DUK_ASSERT(obj->length == 0);  /* Array .length starts at zero. */
	return ret;
}

DUK_EXTERNAL duk_idx_t duk_push_bare_array(duk_hthread *thr) {
	duk_uint_t flags;
	duk_harray *obj;
	duk_idx_t ret;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
	        DUK_HOBJECT_FLAG_FASTREFS |
	        DUK_HOBJECT_FLAG_ARRAY_PART |
	        DUK_HOBJECT_FLAG_EXOTIC_ARRAY |
	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_ARRAY);

	obj = duk_harray_alloc(thr, flags);
	DUK_ASSERT(obj != NULL);

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HOBJECT_INCREF(thr, obj);  /* XXX: could preallocate with refcount = 1 */
	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	thr->valstack_top++;

	DUK_ASSERT(obj->length == 0);  /* Array .length starts at zero. */
	return ret;
}

DUK_INTERNAL duk_harray *duk_push_harray(duk_hthread *thr) {
	/* XXX: API call could do this directly, cast to void in API macro. */
	duk_harray *a;

	DUK_ASSERT_API_ENTRY(thr);

	(void) duk_push_array(thr);
	DUK_ASSERT(DUK_TVAL_IS_OBJECT(thr->valstack_top - 1));
	a = (duk_harray *) DUK_TVAL_GET_OBJECT(thr->valstack_top - 1);
	DUK_ASSERT(a != NULL);
	return a;
}

/* Push a duk_harray with preallocated size (.length also set to match size).
 * Caller may then populate array part of the duk_harray directly.
 */
DUK_INTERNAL duk_harray *duk_push_harray_with_size(duk_hthread *thr, duk_uint32_t size) {
	duk_harray *a;

	DUK_ASSERT_API_ENTRY(thr);

	a = duk_push_harray(thr);

	duk_hobject_realloc_props(thr,
	                          (duk_hobject *) a,
	                          0,
	                          size,
	                          0,
	                          0);
	a->length = size;
	return a;
}

DUK_INTERNAL duk_tval *duk_push_harray_with_size_outptr(duk_hthread *thr, duk_uint32_t size) {
	duk_harray *a;

	DUK_ASSERT_API_ENTRY(thr);

	a = duk_push_harray_with_size(thr, size);
	DUK_ASSERT(a != NULL);
	return DUK_HOBJECT_A_GET_BASE(thr->heap, (duk_hobject *) a);
}

DUK_EXTERNAL duk_idx_t duk_push_thread_raw(duk_hthread *thr, duk_uint_t flags) {
	duk_hthread *obj;
	duk_idx_t ret;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	DUK__CHECK_SPACE();

	obj = duk_hthread_alloc(thr,
	                        DUK_HOBJECT_FLAG_EXTENSIBLE |
	                        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_THREAD));
	DUK_ASSERT(obj != NULL);
	obj->state = DUK_HTHREAD_STATE_INACTIVE;
#if defined(DUK_USE_ROM_STRINGS)
	/* Nothing to initialize, strs[] is in ROM. */
#else
#if defined(DUK_USE_HEAPPTR16)
	obj->strs16 = thr->strs16;
#else
	obj->strs = thr->strs;
#endif
#endif
	DUK_DDD(DUK_DDDPRINT("created thread object with flags: 0x%08lx", (unsigned long) obj->obj.hdr.h_flags));

	/* make the new thread reachable */
	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HTHREAD_INCREF(thr, obj);
	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	thr->valstack_top++;

	/* important to do this *after* pushing, to make the thread reachable for gc */
	if (DUK_UNLIKELY(!duk_hthread_init_stacks(thr->heap, obj))) {
		DUK_ERROR_ALLOC_FAILED(thr);
		DUK_WO_NORETURN(return 0;);
	}

	/* initialize built-ins - either by copying or creating new ones */
	if (flags & DUK_THREAD_NEW_GLOBAL_ENV) {
		duk_hthread_create_builtin_objects(obj);
	} else {
		duk_hthread_copy_builtin_objects(thr, obj);
	}

	/* default prototype */
	DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, (duk_hobject *) obj, obj->builtins[DUK_BIDX_THREAD_PROTOTYPE]);

	/* Initial stack size satisfies the stack slack constraints so there
	 * is no need to require stack here.
	 */
	DUK_ASSERT(DUK_VALSTACK_INITIAL_SIZE >=
	           DUK_VALSTACK_API_ENTRY_MINIMUM + DUK_VALSTACK_INTERNAL_EXTRA);

	return ret;
}

DUK_INTERNAL duk_hcompfunc *duk_push_hcompfunc(duk_hthread *thr) {
	duk_hcompfunc *obj;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	DUK__CHECK_SPACE();

	/* Template functions are not strictly constructable (they don't
	 * have a "prototype" property for instance), so leave the
	 * DUK_HOBJECT_FLAG_CONSRUCTABLE flag cleared here.
	 */

	obj = duk_hcompfunc_alloc(thr,
	                          DUK_HOBJECT_FLAG_EXTENSIBLE |
	                          DUK_HOBJECT_FLAG_CALLABLE |
	                          DUK_HOBJECT_FLAG_COMPFUNC |
	                          DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION));
	if (DUK_UNLIKELY(obj == NULL)) {
		DUK_ERROR_ALLOC_FAILED(thr);
		DUK_WO_NORETURN(return NULL;);
	}

	DUK_DDD(DUK_DDDPRINT("created compiled function object with flags: 0x%08lx", (unsigned long) obj->obj.hdr.h_flags));

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HOBJECT_INCREF(thr, obj);
	thr->valstack_top++;

	/* default prototype */
	DUK_ASSERT(DUK_HOBJECT_GET_PROTOTYPE(thr->heap, (duk_hobject *) obj) == NULL);
	DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, (duk_hobject *) obj, thr->builtins[DUK_BIDX_FUNCTION_PROTOTYPE]);

	return obj;
}

DUK_INTERNAL duk_hboundfunc *duk_push_hboundfunc(duk_hthread *thr) {
	duk_hboundfunc *obj;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	DUK__CHECK_SPACE();
	obj = duk_hboundfunc_alloc(thr->heap,
	                           DUK_HOBJECT_FLAG_EXTENSIBLE |
	                           DUK_HOBJECT_FLAG_BOUNDFUNC |
	                           DUK_HOBJECT_FLAG_CONSTRUCTABLE |
	                           DUK_HOBJECT_FLAG_CALLABLE |
	                           DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION));
	if (!obj) {
		DUK_ERROR_ALLOC_FAILED(thr);
		DUK_WO_NORETURN(return NULL;);
	}

	tv_slot = thr->valstack_top++;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HOBJECT_INCREF(thr, obj);

	/* Prototype is left as NULL because the caller always sets it (and
	 * it depends on the target function).
	 */
	DUK_ASSERT(DUK_HOBJECT_GET_PROTOTYPE(thr->heap, (duk_hobject *) obj) == NULL);

	return obj;
}

DUK_LOCAL duk_idx_t duk__push_c_function_raw(duk_hthread *thr, duk_c_function func, duk_idx_t nargs, duk_uint_t flags, duk_small_uint_t proto_bidx) {
	duk_hnatfunc *obj;
	duk_idx_t ret;
	duk_tval *tv_slot;
	duk_int16_t func_nargs;

	DUK_CTX_ASSERT_VALID(thr);

	DUK__CHECK_SPACE();

	if (DUK_UNLIKELY(func == NULL)) {
		goto api_error;
	}
	if (nargs >= 0 && nargs < DUK_HNATFUNC_NARGS_MAX) {
		func_nargs = (duk_int16_t) nargs;
	} else if (nargs == DUK_VARARGS) {
		func_nargs = DUK_HNATFUNC_NARGS_VARARGS;
	} else {
		goto api_error;
	}

	obj = duk_hnatfunc_alloc(thr, flags);
	DUK_ASSERT(obj != NULL);

	obj->func = func;
	obj->nargs = func_nargs;

	DUK_DDD(DUK_DDDPRINT("created native function object with flags: 0x%08lx, nargs=%ld",
	                     (unsigned long) obj->obj.hdr.h_flags, (long) obj->nargs));

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HOBJECT_INCREF(thr, obj);
	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	thr->valstack_top++;

	DUK_ASSERT_BIDX_VALID(proto_bidx);
	DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, (duk_hobject *) obj, thr->builtins[proto_bidx]);
	return ret;

 api_error:
	DUK_ERROR_TYPE_INVALID_ARGS(thr);
	DUK_WO_NORETURN(return 0;);
}

DUK_EXTERNAL duk_idx_t duk_push_c_function(duk_hthread *thr, duk_c_function func, duk_int_t nargs) {
	duk_uint_t flags;

	DUK_ASSERT_API_ENTRY(thr);

	flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
	        DUK_HOBJECT_FLAG_CONSTRUCTABLE |
	        DUK_HOBJECT_FLAG_CALLABLE |
	        DUK_HOBJECT_FLAG_FASTREFS |
	        DUK_HOBJECT_FLAG_NATFUNC |
	        DUK_HOBJECT_FLAG_NEWENV |
	        DUK_HOBJECT_FLAG_STRICT |
	        DUK_HOBJECT_FLAG_NOTAIL |
	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);

	/* Default prototype is a Duktape specific %NativeFunctionPrototype%
	 * which provides .length and .name getters.
	 */
	return duk__push_c_function_raw(thr, func, nargs, flags, DUK_BIDX_NATIVE_FUNCTION_PROTOTYPE);
}

DUK_INTERNAL void duk_push_c_function_builtin(duk_hthread *thr, duk_c_function func, duk_int_t nargs) {
	duk_uint_t flags;

	DUK_ASSERT_API_ENTRY(thr);

	flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
	        DUK_HOBJECT_FLAG_CONSTRUCTABLE |
	        DUK_HOBJECT_FLAG_CALLABLE |
	        DUK_HOBJECT_FLAG_FASTREFS |
	        DUK_HOBJECT_FLAG_NATFUNC |
	        DUK_HOBJECT_FLAG_NEWENV |
	        DUK_HOBJECT_FLAG_STRICT |
	        DUK_HOBJECT_FLAG_NOTAIL |
	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);

	/* Must use Function.prototype for standard built-in functions. */
	(void) duk__push_c_function_raw(thr, func, nargs, flags, DUK_BIDX_FUNCTION_PROTOTYPE);
}

DUK_INTERNAL void duk_push_c_function_builtin_noconstruct(duk_hthread *thr, duk_c_function func, duk_int_t nargs) {
	duk_uint_t flags;

	DUK_ASSERT_API_ENTRY(thr);

	flags = DUK_HOBJECT_FLAG_EXTENSIBLE |
	        DUK_HOBJECT_FLAG_CALLABLE |
	        DUK_HOBJECT_FLAG_FASTREFS |
	        DUK_HOBJECT_FLAG_NATFUNC |
	        DUK_HOBJECT_FLAG_NEWENV |
	        DUK_HOBJECT_FLAG_STRICT |
	        DUK_HOBJECT_FLAG_NOTAIL |
	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);

	/* Must use Function.prototype for standard built-in functions. */
	(void) duk__push_c_function_raw(thr, func, nargs, flags, DUK_BIDX_FUNCTION_PROTOTYPE);
}

DUK_EXTERNAL duk_idx_t duk_push_c_lightfunc(duk_hthread *thr, duk_c_function func, duk_idx_t nargs, duk_idx_t length, duk_int_t magic) {
	duk_small_uint_t lf_flags;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);

	DUK__CHECK_SPACE();

	if (nargs >= DUK_LFUNC_NARGS_MIN && nargs <= DUK_LFUNC_NARGS_MAX) {
		/* as is */
	} else if (nargs == DUK_VARARGS) {
		nargs = DUK_LFUNC_NARGS_VARARGS;
	} else {
		goto api_error;
	}
	if (DUK_UNLIKELY(!(length >= DUK_LFUNC_LENGTH_MIN && length <= DUK_LFUNC_LENGTH_MAX))) {
		goto api_error;
	}
	if (DUK_UNLIKELY(!(magic >= DUK_LFUNC_MAGIC_MIN && magic <= DUK_LFUNC_MAGIC_MAX))) {
		goto api_error;
	}

	lf_flags = DUK_LFUNC_FLAGS_PACK((duk_small_int_t) magic, (duk_small_uint_t) length, (duk_small_uint_t) nargs);
	tv_slot = thr->valstack_top++;
	DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(tv_slot));
	DUK_TVAL_SET_LIGHTFUNC(tv_slot, func, lf_flags);
	DUK_ASSERT(tv_slot >= thr->valstack_bottom);
	return (duk_idx_t) (tv_slot - thr->valstack_bottom);

 api_error:
	DUK_ERROR_TYPE_INVALID_ARGS(thr);
	DUK_WO_NORETURN(return 0;);
}

#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
DUK_INTERNAL duk_hbufobj *duk_push_bufobj_raw(duk_hthread *thr, duk_uint_t hobject_flags_and_class, duk_small_int_t prototype_bidx) {
	duk_hbufobj *obj;
	duk_tval *tv_slot;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(prototype_bidx >= 0);

	DUK__CHECK_SPACE();

	obj = duk_hbufobj_alloc(thr, hobject_flags_and_class);
	DUK_ASSERT(obj != NULL);

	DUK_HOBJECT_SET_PROTOTYPE_INIT_INCREF(thr, (duk_hobject *) obj, thr->builtins[prototype_bidx]);
	DUK_HBUFOBJ_ASSERT_VALID(obj);

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) obj);
	DUK_HOBJECT_INCREF(thr, obj);
	thr->valstack_top++;

	return obj;
}
#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */

/* XXX: There's quite a bit of overlap with buffer creation handling in
 * duk_bi_buffer.c.  Look for overlap and refactor.
 */
#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
#define DUK__PACK_ARGS(classnum,protobidx,elemtype,elemshift,istypedarray) \
	(((classnum) << 24) | ((protobidx) << 16) | ((elemtype) << 8) | ((elemshift) << 4) | (istypedarray))

static const duk_uint32_t duk__bufobj_flags_lookup[] = {
	/* Node.js Buffers are Uint8Array instances which inherit from Buffer.prototype. */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_ARRAYBUFFER,       DUK_BIDX_ARRAYBUFFER_PROTOTYPE,       DUK_HBUFOBJ_ELEM_UINT8,        0, 0),  /* DUK_BUFOBJ_ARRAYBUFFER */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_UINT8ARRAY,        DUK_BIDX_NODEJS_BUFFER_PROTOTYPE,     DUK_HBUFOBJ_ELEM_UINT8,        0, 1),  /* DUK_BUFOBJ_NODEJS_BUFFER */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_DATAVIEW,          DUK_BIDX_DATAVIEW_PROTOTYPE,          DUK_HBUFOBJ_ELEM_UINT8,        0, 0),  /* DUK_BUFOBJ_DATAVIEW */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_INT8ARRAY,         DUK_BIDX_INT8ARRAY_PROTOTYPE,         DUK_HBUFOBJ_ELEM_INT8,         0, 1),  /* DUK_BUFOBJ_INT8ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_UINT8ARRAY,        DUK_BIDX_UINT8ARRAY_PROTOTYPE,        DUK_HBUFOBJ_ELEM_UINT8,        0, 1),  /* DUK_BUFOBJ_UINT8ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_UINT8CLAMPEDARRAY, DUK_BIDX_UINT8CLAMPEDARRAY_PROTOTYPE, DUK_HBUFOBJ_ELEM_UINT8CLAMPED, 0, 1),  /* DUK_BUFOBJ_UINT8CLAMPEDARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_INT16ARRAY,        DUK_BIDX_INT16ARRAY_PROTOTYPE,        DUK_HBUFOBJ_ELEM_INT16,        1, 1),  /* DUK_BUFOBJ_INT16ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_UINT16ARRAY,       DUK_BIDX_UINT16ARRAY_PROTOTYPE,       DUK_HBUFOBJ_ELEM_UINT16,       1, 1),  /* DUK_BUFOBJ_UINT16ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_INT32ARRAY,        DUK_BIDX_INT32ARRAY_PROTOTYPE,        DUK_HBUFOBJ_ELEM_INT32,        2, 1),  /* DUK_BUFOBJ_INT32ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_UINT32ARRAY,       DUK_BIDX_UINT32ARRAY_PROTOTYPE,       DUK_HBUFOBJ_ELEM_UINT32,       2, 1),  /* DUK_BUFOBJ_UINT32ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_FLOAT32ARRAY,      DUK_BIDX_FLOAT32ARRAY_PROTOTYPE,      DUK_HBUFOBJ_ELEM_FLOAT32,      2, 1),  /* DUK_BUFOBJ_FLOAT32ARRAY */
	DUK__PACK_ARGS(DUK_HOBJECT_CLASS_FLOAT64ARRAY,      DUK_BIDX_FLOAT64ARRAY_PROTOTYPE,      DUK_HBUFOBJ_ELEM_FLOAT64,      3, 1)   /* DUK_BUFOBJ_FLOAT64ARRAY */
};
#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */

#if defined(DUK_USE_BUFFEROBJECT_SUPPORT)
DUK_EXTERNAL void duk_push_buffer_object(duk_hthread *thr, duk_idx_t idx_buffer, duk_size_t byte_offset, duk_size_t byte_length, duk_uint_t flags) {
	duk_hbufobj *h_bufobj;
	duk_hbuffer *h_val;
	duk_hobject *h_arraybuf;
	duk_uint32_t tmp;
	duk_uint_t classnum;
	duk_uint_t protobidx;
	duk_uint_t lookupidx;
	duk_uint_t uint_offset, uint_length, uint_added;

	DUK_ASSERT_API_ENTRY(thr);

	/* The underlying types for offset/length in duk_hbufobj is
	 * duk_uint_t; make sure argument values fit.
	 */
	uint_offset = (duk_uint_t) byte_offset;
	uint_length = (duk_uint_t) byte_length;
	if (sizeof(duk_size_t) != sizeof(duk_uint_t)) {
		if (DUK_UNLIKELY((duk_size_t) uint_offset != byte_offset || (duk_size_t) uint_length != byte_length)) {
			goto range_error;
		}
	}

	DUK_ASSERT_DISABLE(flags >= 0);  /* flags is unsigned */
	lookupidx = flags;
	if (DUK_UNLIKELY(lookupidx >= sizeof(duk__bufobj_flags_lookup) / sizeof(duk_uint32_t))) {
		goto arg_error;
	}
	tmp = duk__bufobj_flags_lookup[lookupidx];
	classnum = tmp >> 24;
	protobidx = (tmp >> 16) & 0xff;

	h_arraybuf = duk_get_hobject(thr, idx_buffer);
	if (h_arraybuf != NULL &&  /* argument is an object */
	    flags != DUK_BUFOBJ_ARRAYBUFFER &&  /* creating a view */
	    DUK_HOBJECT_GET_CLASS_NUMBER(h_arraybuf) == DUK_HOBJECT_CLASS_ARRAYBUFFER  /* argument is ArrayBuffer */) {
		duk_uint_t tmp_offset;

		DUK_HBUFOBJ_ASSERT_VALID((duk_hbufobj *) h_arraybuf);
		h_val = ((duk_hbufobj *) h_arraybuf)->buf;
		if (DUK_UNLIKELY(h_val == NULL)) {
			goto arg_error;
		}

		tmp_offset = uint_offset + ((duk_hbufobj *) h_arraybuf)->offset;
		if (DUK_UNLIKELY(tmp_offset < uint_offset)) {
			goto range_error;
		}
		uint_offset = tmp_offset;

		/* Note intentional difference to new TypedArray(): we allow
		 * caller to create an uncovered typed array (which is memory
		 * safe); new TypedArray() rejects it.
		 */
	} else {
		/* Handle unexpected object arguments here too, for nice error
		 * messages.
		 */
		h_arraybuf = NULL;
		h_val = duk_require_hbuffer(thr, idx_buffer);
	}

	/* Wrap check for offset+length. */
	uint_added = uint_offset + uint_length;
	if (DUK_UNLIKELY(uint_added < uint_offset)) {
		goto range_error;
	}
	DUK_ASSERT(uint_added >= uint_offset && uint_added >= uint_length);

	DUK_ASSERT(h_val != NULL);

	h_bufobj = duk_push_bufobj_raw(thr,
	                               DUK_HOBJECT_FLAG_EXTENSIBLE |
	                               DUK_HOBJECT_FLAG_BUFOBJ |
	                               DUK_HOBJECT_CLASS_AS_FLAGS(classnum),
	                               (duk_small_int_t) protobidx);
	DUK_ASSERT(h_bufobj != NULL);

	h_bufobj->buf = h_val;
	DUK_HBUFFER_INCREF(thr, h_val);
	h_bufobj->buf_prop = h_arraybuf;
	DUK_HOBJECT_INCREF_ALLOWNULL(thr, h_arraybuf);
	h_bufobj->offset = uint_offset;
	h_bufobj->length = uint_length;
	h_bufobj->shift = (tmp >> 4) & 0x0f;
	h_bufobj->elem_type = (tmp >> 8) & 0xff;
	h_bufobj->is_typedarray = tmp & 0x0f;
	DUK_HBUFOBJ_ASSERT_VALID(h_bufobj);

	/* TypedArray views need an automatic ArrayBuffer which must be
	 * provided as .buffer property of the view.  The ArrayBuffer is
	 * referenced via duk_hbufobj->buf_prop and an inherited .buffer
	 * accessor returns it.  The ArrayBuffer is created lazily on first
	 * access if necessary so we don't need to do anything more here.
	 */
	return;

 range_error:
	DUK_ERROR_RANGE(thr, DUK_STR_INVALID_ARGS);
	DUK_WO_NORETURN(return;);

 arg_error:
	DUK_ERROR_TYPE(thr, DUK_STR_INVALID_ARGS);
	DUK_WO_NORETURN(return;);
}
#else  /* DUK_USE_BUFFEROBJECT_SUPPORT */
DUK_EXTERNAL void duk_push_buffer_object(duk_hthread *thr, duk_idx_t idx_buffer, duk_size_t byte_offset, duk_size_t byte_length, duk_uint_t flags) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_UNREF(idx_buffer);
	DUK_UNREF(byte_offset);
	DUK_UNREF(byte_length);
	DUK_UNREF(flags);
	DUK_ERROR_UNSUPPORTED(thr);
	DUK_WO_NORETURN(return;);
}
#endif  /* DUK_USE_BUFFEROBJECT_SUPPORT */

DUK_EXTERNAL duk_idx_t duk_push_error_object_va_raw(duk_hthread *thr, duk_errcode_t err_code, const char *filename, duk_int_t line, const char *fmt, va_list ap) {
	duk_hobject *proto;
#if defined(DUK_USE_AUGMENT_ERROR_CREATE)
	duk_small_uint_t augment_flags;
#endif

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr != NULL);
	DUK_UNREF(filename);
	DUK_UNREF(line);

	/* Error code also packs a tracedata related flag. */
#if defined(DUK_USE_AUGMENT_ERROR_CREATE)
	augment_flags = 0;
	if (err_code & DUK_ERRCODE_FLAG_NOBLAME_FILELINE) {
		augment_flags = DUK_AUGMENT_FLAG_NOBLAME_FILELINE;
	}
#endif
	err_code = err_code & (~DUK_ERRCODE_FLAG_NOBLAME_FILELINE);

	/* error gets its 'name' from the prototype */
	proto = duk_error_prototype_from_code(thr, err_code);
	(void) duk_push_object_helper_proto(thr,
	                                    DUK_HOBJECT_FLAG_EXTENSIBLE |
	                                    DUK_HOBJECT_FLAG_FASTREFS |
	                                    DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_ERROR),
	                                    proto);

	/* ... and its 'message' from an instance property */
	if (fmt) {
		duk_push_vsprintf(thr, fmt, ap);
		duk_xdef_prop_stridx_short(thr, -2, DUK_STRIDX_MESSAGE, DUK_PROPDESC_FLAGS_WC);
	} else {
		/* If no explicit message given, put error code into message field
		 * (as a number).  This is not fully in keeping with the ECMAScript
		 * error model because messages are supposed to be strings (Error
		 * constructors use ToString() on their argument).  However, it's
		 * probably more useful than having a separate 'code' property.
		 */
		duk_push_int(thr, err_code);
		duk_xdef_prop_stridx_short(thr, -2, DUK_STRIDX_MESSAGE, DUK_PROPDESC_FLAGS_WC);
	}

	/* XXX: .code = err_code disabled, not sure if useful */

	/* Creation time error augmentation */
#if defined(DUK_USE_AUGMENT_ERROR_CREATE)
	/* filename may be NULL in which case file/line is not recorded */
	duk_err_augment_error_create(thr, thr, filename, line, augment_flags);  /* may throw an error */
#endif

	return duk_get_top_index_unsafe(thr);
}

DUK_EXTERNAL duk_idx_t duk_push_error_object_raw(duk_hthread *thr, duk_errcode_t err_code, const char *filename, duk_int_t line, const char *fmt, ...) {
	va_list ap;
	duk_idx_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	va_start(ap, fmt);
	ret = duk_push_error_object_va_raw(thr, err_code, filename, line, fmt, ap);
	va_end(ap);
	return ret;
}

#if !defined(DUK_USE_VARIADIC_MACROS)
DUK_EXTERNAL duk_idx_t duk_push_error_object_stash(duk_hthread *thr, duk_errcode_t err_code, const char *fmt, ...) {
	const char *filename = duk_api_global_filename;
	duk_int_t line = duk_api_global_line;
	va_list ap;
	duk_idx_t ret;

	DUK_ASSERT_API_ENTRY(thr);

	duk_api_global_filename = NULL;
	duk_api_global_line = 0;
	va_start(ap, fmt);
	ret = duk_push_error_object_va_raw(thr, err_code, filename, line, fmt, ap);
	va_end(ap);
	return ret;
}
#endif  /* DUK_USE_VARIADIC_MACROS */

DUK_EXTERNAL void *duk_push_buffer_raw(duk_hthread *thr, duk_size_t size, duk_small_uint_t flags) {
	duk_tval *tv_slot;
	duk_hbuffer *h;
	void *buf_data;

	DUK_ASSERT_API_ENTRY(thr);

	DUK__CHECK_SPACE();

	/* Check for maximum buffer length. */
	if (DUK_UNLIKELY(size > DUK_HBUFFER_MAX_BYTELEN)) {
		DUK_ERROR_RANGE(thr, DUK_STR_BUFFER_TOO_LONG);
		DUK_WO_NORETURN(return NULL;);
	}

	h = duk_hbuffer_alloc(thr->heap, size, flags, &buf_data);
	if (DUK_UNLIKELY(h == NULL)) {
		DUK_ERROR_ALLOC_FAILED(thr);
		DUK_WO_NORETURN(return NULL;);
	}

	tv_slot = thr->valstack_top;
	DUK_TVAL_SET_BUFFER(tv_slot, h);
	DUK_HBUFFER_INCREF(thr, h);
	thr->valstack_top++;

	return (void *) buf_data;
}

DUK_INTERNAL void *duk_push_fixed_buffer_nozero(duk_hthread *thr, duk_size_t len) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_push_buffer_raw(thr, len, DUK_BUF_FLAG_NOZERO);
}

DUK_INTERNAL void *duk_push_fixed_buffer_zero(duk_hthread *thr, duk_size_t len) {
	void *ptr;

	DUK_ASSERT_API_ENTRY(thr);

	ptr = duk_push_buffer_raw(thr, len, 0);
	DUK_ASSERT(ptr != NULL);
#if !defined(DUK_USE_ZERO_BUFFER_DATA)
	/* ES2015 requires zeroing even when DUK_USE_ZERO_BUFFER_DATA
	 * is not set.
	 */
	duk_memzero((void *) ptr, (size_t) len);
#endif
	return ptr;
}

#if defined(DUK_USE_ES6_PROXY)
DUK_EXTERNAL duk_idx_t duk_push_proxy(duk_hthread *thr, duk_uint_t proxy_flags) {
	duk_hobject *h_target;
	duk_hobject *h_handler;
	duk_hproxy *h_proxy;
	duk_tval *tv_slot;
	duk_uint_t flags;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_UNREF(proxy_flags);

	/* DUK__CHECK_SPACE() unnecessary because the Proxy is written to
	 * value stack in-place.
	 */
#if 0
	DUK__CHECK_SPACE();
#endif

	/* Reject a proxy object as the target because it would need
	 * special handling in property lookups.  (ES2015 has no such
	 * restriction.)
	 */
	h_target = duk_require_hobject_promote_mask(thr, -2, DUK_TYPE_MASK_LIGHTFUNC | DUK_TYPE_MASK_BUFFER);
	DUK_ASSERT(h_target != NULL);
	if (DUK_HOBJECT_IS_PROXY(h_target)) {
		goto fail_args;
	}

	/* Reject a proxy object as the handler because it would cause
	 * potentially unbounded recursion.  (ES2015 has no such
	 * restriction.)
	 *
	 * There's little practical reason to use a lightfunc or a plain
	 * buffer as the handler table: one could only provide traps via
	 * their prototype objects (Function.prototype and ArrayBuffer.prototype).
	 * Even so, as lightfuncs and plain buffers mimic their object
	 * counterparts, they're promoted and accepted here.
	 */
	h_handler = duk_require_hobject_promote_mask(thr, -1, DUK_TYPE_MASK_LIGHTFUNC | DUK_TYPE_MASK_BUFFER);
	DUK_ASSERT(h_handler != NULL);
	if (DUK_HOBJECT_IS_PROXY(h_handler)) {
		goto fail_args;
	}

	/* XXX: Proxy object currently has no prototype, so ToPrimitive()
	 * coercion fails which is a bit confusing.
	 */

	/* CALLABLE and CONSTRUCTABLE flags are copied from the (initial)
	 * target, see ES2015 Sections 9.5.15 and 9.5.13.
	 */
	flags = DUK_HEAPHDR_GET_FLAGS((duk_heaphdr *) h_target) &
	        (DUK_HOBJECT_FLAG_CALLABLE | DUK_HOBJECT_FLAG_CONSTRUCTABLE);
	flags |= DUK_HOBJECT_FLAG_EXTENSIBLE |
	         DUK_HOBJECT_FLAG_EXOTIC_PROXYOBJ;
	if (flags & DUK_HOBJECT_FLAG_CALLABLE) {
		flags |= DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION) |
		         DUK_HOBJECT_FLAG_SPECIAL_CALL;
	} else {
		flags |= DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_OBJECT);
	}

	h_proxy = duk_hproxy_alloc(thr, flags);
	DUK_ASSERT(h_proxy != NULL);
	DUK_ASSERT(DUK_HOBJECT_GET_PROTOTYPE(thr->heap, (duk_hobject *) h_proxy) == NULL);

	/* Initialize Proxy target and handler references; avoid INCREF
	 * by stealing the value stack refcounts via direct value stack
	 * manipulation.  INCREF is needed for the Proxy itself however.
	 */
	DUK_ASSERT(h_target != NULL);
	h_proxy->target = h_target;
	DUK_ASSERT(h_handler != NULL);
	h_proxy->handler = h_handler;
	DUK_HPROXY_ASSERT_VALID(h_proxy);

	DUK_ASSERT(duk_get_hobject(thr, -2) == h_target);
	DUK_ASSERT(duk_get_hobject(thr, -1) == h_handler);
	tv_slot = thr->valstack_top - 2;
	DUK_ASSERT(tv_slot >= thr->valstack_bottom);
	DUK_TVAL_SET_OBJECT(tv_slot, (duk_hobject *) h_proxy);
	DUK_HOBJECT_INCREF(thr, (duk_hobject *) h_proxy);
	tv_slot++;
	DUK_TVAL_SET_UNDEFINED(tv_slot);  /* [ ... target handler ] -> [ ... proxy undefined ] */
	thr->valstack_top = tv_slot;      /* -> [ ... proxy ] */

	DUK_DD(DUK_DDPRINT("created Proxy: %!iT", duk_get_tval(thr, -1)));

	return (duk_idx_t) (thr->valstack_top - thr->valstack_bottom - 1);

 fail_args:
	DUK_ERROR_TYPE_INVALID_ARGS(thr);
	DUK_WO_NORETURN(return 0;);
}
#else  /* DUK_USE_ES6_PROXY */
DUK_EXTERNAL duk_idx_t duk_push_proxy(duk_hthread *thr, duk_uint_t proxy_flags) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_UNREF(proxy_flags);
	DUK_ERROR_UNSUPPORTED(thr);
	DUK_WO_NORETURN(return 0;);
}
#endif  /* DUK_USE_ES6_PROXY */

#if defined(DUK_USE_ASSERTIONS)
DUK_LOCAL void duk__validate_push_heapptr(duk_hthread *thr, void *ptr) {
	duk_heaphdr *h;
	duk_heaphdr *curr;
	duk_bool_t found = 0;

	h = (duk_heaphdr *) ptr;
	if (h == NULL) {
		/* Allowed. */
		return;
	}
	DUK_ASSERT(h != NULL);
	DUK_ASSERT(DUK_HEAPHDR_HTYPE_VALID(h));

	/* One particular problem case is where an object has been
	 * queued for finalization but the finalizer hasn't yet been
	 * executed.
	 *
	 * Corner case: we're running in a finalizer for object X, and
	 * user code calls duk_push_heapptr() for X itself.  In this
	 * case X will be in finalize_list, and we can detect the case
	 * by seeing that X's FINALIZED flag is set (which is done before
	 * the finalizer starts executing).
	 */
#if defined(DUK_USE_FINALIZER_SUPPORT)
	for (curr = thr->heap->finalize_list;
	     curr != NULL;
	     curr = DUK_HEAPHDR_GET_NEXT(thr->heap, curr)) {
		/* FINALIZABLE is set for all objects on finalize_list
		 * except for an object being finalized right now.  So
		 * can't assert here.
		 */
#if 0
		DUK_ASSERT(DUK_HEAPHDR_HAS_FINALIZABLE(curr));
#endif

		if (curr == h) {
			if (DUK_HEAPHDR_HAS_FINALIZED((duk_heaphdr *) h)) {
				/* Object is currently being finalized. */
				DUK_ASSERT(found == 0);  /* Would indicate corrupted lists. */
				found = 1;
			} else {
				/* Not being finalized but on finalize_list,
				 * allowed since Duktape 2.1.
				 */
				DUK_ASSERT(found == 0);  /* Would indicate corrupted lists. */
				found = 1;
			}
		}
	}
#endif  /* DUK_USE_FINALIZER_SUPPORT */

#if defined(DUK_USE_REFERENCE_COUNTING)
	/* Because refzero_list is now processed to completion inline with
	 * no side effects, it's always empty here.
	 */
	DUK_ASSERT(thr->heap->refzero_list == NULL);
#endif

	/* If not present in finalize_list (or refzero_list), it
	 * must be either in heap_allocated or the string table.
	 */
	if (DUK_HEAPHDR_IS_STRING(h)) {
		duk_uint32_t i;
		duk_hstring *str;
		duk_heap *heap = thr->heap;

		DUK_ASSERT(found == 0);
		for (i = 0; i < heap->st_size; i++) {
#if defined(DUK_USE_STRTAB_PTRCOMP)
			str = DUK_USE_HEAPPTR_DEC16((heap)->heap_udata, heap->strtable16[i]);
#else
			str = heap->strtable[i];
#endif
			while (str != NULL) {
				if (str == (duk_hstring *) h) {
					DUK_ASSERT(found == 0);  /* Would indicate corrupted lists. */
					found = 1;
					break;
				}
				str = str->hdr.h_next;
			}
		}
		DUK_ASSERT(found != 0);
	} else {
		for (curr = thr->heap->heap_allocated;
		     curr != NULL;
		     curr = DUK_HEAPHDR_GET_NEXT(thr->heap, curr)) {
			if (curr == h) {
				DUK_ASSERT(found == 0);  /* Would indicate corrupted lists. */
				found = 1;
			}
		}
		DUK_ASSERT(found != 0);
	}
}
#endif  /* DUK_USE_ASSERTIONS */

DUK_EXTERNAL duk_idx_t duk_push_heapptr(duk_hthread *thr, void *ptr) {
	duk_idx_t ret;
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	/* Reviving an object using a heap pointer is a dangerous API
	 * operation: if the application doesn't guarantee that the
	 * pointer target is always reachable, difficult-to-diagnose
	 * problems may ensue.  Try to validate the 'ptr' argument to
	 * the extent possible.
	 */

#if defined(DUK_USE_ASSERTIONS)
	duk__validate_push_heapptr(thr, ptr);
#endif

	DUK__CHECK_SPACE();

	ret = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	tv = thr->valstack_top++;

	if (ptr == NULL) {
		DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(tv));
		return ret;
	}

	DUK_HEAPHDR_ASSERT_VALID((duk_heaphdr *) ptr);

	/* If the argument is on finalize_list it has technically been
	 * unreachable before duk_push_heapptr() but it's still safe to
	 * push it.  Starting from Duktape 2.1 allow application code to
	 * do so.  There are two main cases:
	 *
	 *   (1) The object is on the finalize_list and we're called by
	 *       the finalizer for the object being finalized.  In this
	 *       case do nothing: finalize_list handling will deal with
	 *       the object queueing.  This is detected by the object not
	 *       having a FINALIZABLE flag despite being on the finalize_list;
	 *       the flag is cleared for the object being finalized only.
	 *
	 *   (2) The object is on the finalize_list but is not currently
	 *       being processed.  In this case the object can be queued
	 *       back to heap_allocated with a few flags cleared, in effect
	 *       cancelling the finalizer.
	 */
	if (DUK_UNLIKELY(DUK_HEAPHDR_HAS_FINALIZABLE((duk_heaphdr *) ptr))) {
		duk_heaphdr *curr;

		DUK_D(DUK_DPRINT("duk_push_heapptr() with a pointer on finalize_list, autorescue"));

		curr = (duk_heaphdr *) ptr;
		DUK_HEAPHDR_CLEAR_FINALIZABLE(curr);

		/* Because FINALIZED is set prior to finalizer call, it will
		 * be set for the object being currently finalized, but not
		 * for other objects on finalize_list.
		 */
		DUK_HEAPHDR_CLEAR_FINALIZED(curr);

		/* Dequeue object from finalize_list and queue it back to
		 * heap_allocated.
		 */
#if defined(DUK_USE_REFERENCE_COUNTING)
		DUK_ASSERT(DUK_HEAPHDR_GET_REFCOUNT(curr) >= 1);  /* Preincremented on finalize_list insert. */
		DUK_HEAPHDR_PREDEC_REFCOUNT(curr);
#endif
		DUK_HEAP_REMOVE_FROM_FINALIZE_LIST(thr->heap, curr);
		DUK_HEAP_INSERT_INTO_HEAP_ALLOCATED(thr->heap, curr);

		/* Continue with the rest. */
	}

	switch (DUK_HEAPHDR_GET_TYPE((duk_heaphdr *) ptr)) {
	case DUK_HTYPE_STRING:
		DUK_TVAL_SET_STRING(tv, (duk_hstring *) ptr);
		break;
	case DUK_HTYPE_OBJECT:
		DUK_TVAL_SET_OBJECT(tv, (duk_hobject *) ptr);
		break;
	default:
		DUK_ASSERT(DUK_HEAPHDR_GET_TYPE((duk_heaphdr *) ptr) == DUK_HTYPE_BUFFER);
		DUK_TVAL_SET_BUFFER(tv, (duk_hbuffer *) ptr);
		break;
	}

	DUK_HEAPHDR_INCREF(thr, (duk_heaphdr *) ptr);

	return ret;
}

/* Push object with no prototype, i.e. a "bare" object. */
DUK_EXTERNAL duk_idx_t duk_push_bare_object(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	(void) duk_push_object_helper(thr,
	                              DUK_HOBJECT_FLAG_EXTENSIBLE |
	                              DUK_HOBJECT_FLAG_FASTREFS |
	                              DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_OBJECT),
	                              -1);  /* no prototype */
	return duk_get_top_index_unsafe(thr);
}

DUK_INTERNAL void duk_push_hstring(duk_hthread *thr, duk_hstring *h) {
	duk_tval tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(h != NULL);

	DUK_TVAL_SET_STRING(&tv, h);
	duk_push_tval(thr, &tv);
}

DUK_INTERNAL void duk_push_hstring_stridx(duk_hthread *thr, duk_small_uint_t stridx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT_STRIDX_VALID(stridx);
	duk_push_hstring(thr, DUK_HTHREAD_GET_STRING(thr, stridx));
}

DUK_INTERNAL void duk_push_hstring_empty(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_push_hstring(thr, DUK_HTHREAD_GET_STRING(thr, DUK_STRIDX_EMPTY_STRING));
}

DUK_INTERNAL void duk_push_hobject(duk_hthread *thr, duk_hobject *h) {
	duk_tval tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(h != NULL);

	DUK_TVAL_SET_OBJECT(&tv, h);
	duk_push_tval(thr, &tv);
}

DUK_INTERNAL void duk_push_hbuffer(duk_hthread *thr, duk_hbuffer *h) {
	duk_tval tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(h != NULL);

	DUK_TVAL_SET_BUFFER(&tv, h);
	duk_push_tval(thr, &tv);
}

DUK_INTERNAL void duk_push_hobject_bidx(duk_hthread *thr, duk_small_int_t builtin_idx) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(builtin_idx >= 0 && builtin_idx < DUK_NUM_BUILTINS);
	DUK_ASSERT(thr->builtins[builtin_idx] != NULL);

	duk_push_hobject(thr, thr->builtins[builtin_idx]);
}

/*
 *  Poppers
 */

DUK_LOCAL DUK_ALWAYS_INLINE void duk__pop_n_unsafe_raw(duk_hthread *thr, duk_idx_t count) {
	duk_tval *tv;
#if defined(DUK_USE_REFERENCE_COUNTING)
	duk_tval *tv_end;
#endif

	DUK_CTX_ASSERT_VALID(thr);
	DUK_ASSERT(count >= 0);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) count);

#if defined(DUK_USE_REFERENCE_COUNTING)
	tv = thr->valstack_top;
	tv_end = tv - count;
	while (tv != tv_end) {
		tv--;
		DUK_ASSERT(tv >= thr->valstack_bottom);
		DUK_TVAL_SET_UNDEFINED_UPDREF_NORZ(thr, tv);
	}
	thr->valstack_top = tv;
	DUK_REFZERO_CHECK_FAST(thr);
#else
	tv = thr->valstack_top;
	while (count > 0) {
		count--;
		tv--;
		DUK_ASSERT(tv >= thr->valstack_bottom);
		DUK_TVAL_SET_UNDEFINED(tv);
	}
	thr->valstack_top = tv;
#endif

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}

DUK_EXTERNAL void duk_pop_n(duk_hthread *thr, duk_idx_t count) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);

	if (DUK_UNLIKELY((duk_uidx_t) (thr->valstack_top - thr->valstack_bottom) < (duk_uidx_t) count)) {
		DUK_ERROR_RANGE_INVALID_COUNT(thr);
		DUK_WO_NORETURN(return;);
	}
	DUK_ASSERT(count >= 0);

	duk__pop_n_unsafe_raw(thr, count);
}

#if defined(DUK_USE_PREFER_SIZE)
DUK_INTERNAL void duk_pop_n_unsafe(duk_hthread *thr, duk_idx_t count) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n(thr, count);
}
#else  /* DUK_USE_PREFER_SIZE */
DUK_INTERNAL void duk_pop_n_unsafe(duk_hthread *thr, duk_idx_t count) {
	DUK_ASSERT_API_ENTRY(thr);
	duk__pop_n_unsafe_raw(thr, count);
}
#endif  /* DUK_USE_PREFER_SIZE */

/* Pop N elements without DECREF (in effect "stealing" any actual refcounts). */
#if defined(DUK_USE_REFERENCE_COUNTING)
DUK_INTERNAL void duk_pop_n_nodecref_unsafe(duk_hthread *thr, duk_idx_t count) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(count >= 0);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) count);

	tv = thr->valstack_top;
	while (count > 0) {
		count--;
		tv--;
		DUK_ASSERT(tv >= thr->valstack_bottom);
		DUK_TVAL_SET_UNDEFINED(tv);
	}
	thr->valstack_top = tv;

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}
#else  /* DUK_USE_REFERENCE_COUNTING */
DUK_INTERNAL void duk_pop_n_nodecref_unsafe(duk_hthread *thr, duk_idx_t count) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_unsafe(thr, count);
}
#endif  /* DUK_USE_REFERENCE_COUNTING */

/* Popping one element is called so often that when footprint is not an issue,
 * compile a specialized function for it.
 */
#if defined(DUK_USE_PREFER_SIZE)
DUK_EXTERNAL void duk_pop(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n(thr, 1);
}
DUK_INTERNAL void duk_pop_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_unsafe(thr, 1);
}
DUK_INTERNAL void duk_pop_nodecref_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_nodecref_unsafe(thr, 1);
}
#else  /* DUK_USE_PREFER_SIZE */
DUK_LOCAL DUK_ALWAYS_INLINE void duk__pop_unsafe_raw(duk_hthread *thr) {
	duk_tval *tv;

	DUK_CTX_ASSERT_VALID(thr);
	DUK_ASSERT(thr->valstack_top != thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) 1);

	tv = --thr->valstack_top;
	DUK_ASSERT(tv >= thr->valstack_bottom);
#if defined(DUK_USE_REFERENCE_COUNTING)
	DUK_TVAL_SET_UNDEFINED_UPDREF(thr, tv);  /* side effects */
#else
	DUK_TVAL_SET_UNDEFINED(tv);
#endif

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}
DUK_EXTERNAL void duk_pop(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	if (DUK_UNLIKELY(thr->valstack_top == thr->valstack_bottom)) {
		DUK_ERROR_RANGE_INVALID_COUNT(thr);
		DUK_WO_NORETURN(return;);
	}

	duk__pop_unsafe_raw(thr);
}
DUK_INTERNAL void duk_pop_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk__pop_unsafe_raw(thr);
}
DUK_INTERNAL void duk_pop_nodecref_unsafe(duk_hthread *thr) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr->valstack_top != thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) 1);

	tv = --thr->valstack_top;
	DUK_ASSERT(tv >= thr->valstack_bottom);
	DUK_TVAL_SET_UNDEFINED(tv);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}
#endif  /* !DUK_USE_PREFER_SIZE */

#if defined(DUK_USE_PREFER_SIZE)
DUK_INTERNAL void duk_pop_undefined(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_nodecref_unsafe(thr);
}
#else  /* DUK_USE_PREFER_SIZE */
DUK_INTERNAL void duk_pop_undefined(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr->valstack_top != thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) 1);

	DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(thr->valstack_top - 1));
	thr->valstack_top--;

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}
#endif  /* !DUK_USE_PREFER_SIZE */

#if defined(DUK_USE_PREFER_SIZE)
DUK_EXTERNAL void duk_pop_2(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n(thr, 2);
}
DUK_INTERNAL void duk_pop_2_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_unsafe(thr, 2);
}
DUK_INTERNAL void duk_pop_2_nodecref_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_nodecref_unsafe(thr, 2);
}
#else
DUK_LOCAL DUK_ALWAYS_INLINE void duk__pop_2_unsafe_raw(duk_hthread *thr) {
	duk_tval *tv;

	DUK_CTX_ASSERT_VALID(thr);
	DUK_ASSERT(thr->valstack_top != thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) 2);

	tv = --thr->valstack_top;
	DUK_ASSERT(tv >= thr->valstack_bottom);
#if defined(DUK_USE_REFERENCE_COUNTING)
	DUK_TVAL_SET_UNDEFINED_UPDREF(thr, tv);  /* side effects */
#else
	DUK_TVAL_SET_UNDEFINED(tv);
#endif
	tv = --thr->valstack_top;
	DUK_ASSERT(tv >= thr->valstack_bottom);
#if defined(DUK_USE_REFERENCE_COUNTING)
	DUK_TVAL_SET_UNDEFINED_UPDREF(thr, tv);  /* side effects */
#else
	DUK_TVAL_SET_UNDEFINED(tv);
#endif

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}
DUK_EXTERNAL void duk_pop_2(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	if (DUK_UNLIKELY(thr->valstack_top - 2 < thr->valstack_bottom)) {
		DUK_ERROR_RANGE_INVALID_COUNT(thr);
		DUK_WO_NORETURN(return;);
	}

	duk__pop_2_unsafe_raw(thr);
}
DUK_INTERNAL void duk_pop_2_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk__pop_2_unsafe_raw(thr);
}
DUK_INTERNAL void duk_pop_2_nodecref_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr->valstack_top != thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT((duk_size_t) (thr->valstack_top - thr->valstack_bottom) >= (duk_size_t) 2);

	DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(thr->valstack_top - 1));
	DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(thr->valstack_top - 2));
	thr->valstack_top -= 2;

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
}
#endif  /* !DUK_USE_PREFER_SIZE */

DUK_EXTERNAL void duk_pop_3(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n(thr, 3);
}

DUK_INTERNAL void duk_pop_3_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_unsafe(thr, 3);
}

DUK_INTERNAL void duk_pop_3_nodecref_unsafe(duk_hthread *thr) {
	DUK_ASSERT_API_ENTRY(thr);
	duk_pop_n_nodecref_unsafe(thr, 3);
}

/*
 *  Pack and unpack (pack value stack entries into an array and vice versa)
 */

/* XXX: pack index range? array index offset? */
/* XXX: need ability to pack into a bare array? */
DUK_INTERNAL void duk_pack(duk_hthread *thr, duk_idx_t count) {
	duk_tval *tv_src;
	duk_tval *tv_dst;
	duk_tval *tv_curr;
	duk_tval *tv_limit;
	duk_idx_t top;

	DUK_ASSERT_API_ENTRY(thr);

	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	top = (duk_idx_t) (thr->valstack_top - thr->valstack_bottom);
	DUK_ASSERT(top >= 0);
	if (DUK_UNLIKELY((duk_uidx_t) count > (duk_uidx_t) top)) {
		/* Also handles negative count. */
		DUK_ERROR_RANGE_INVALID_COUNT(thr);
		DUK_WO_NORETURN(return;);
	}
	DUK_ASSERT(count >= 0);

	/* Wrapping is controlled by the check above: value stack top can be
	 * at most DUK_USE_VALSTACK_LIMIT which is low enough so that
	 * multiplying with sizeof(duk_tval) won't wrap.
	 */
	DUK_ASSERT(count >= 0 && count <= (duk_idx_t) DUK_USE_VALSTACK_LIMIT);
	DUK_ASSERT((duk_size_t) count <= DUK_SIZE_MAX / sizeof(duk_tval));  /* no wrapping */

	tv_dst = duk_push_harray_with_size_outptr(thr, (duk_uint32_t) count);  /* XXX: uninitialized would be OK */
	DUK_ASSERT(count == 0 || tv_dst != NULL);
	DUK_ASSERT(!duk_is_bare_object(thr, -1));

	/* Copy value stack values directly to the array part without
	 * any refcount updates: net refcount changes are zero.
	 */
	tv_src = thr->valstack_top - count - 1;
	duk_memcpy_unsafe((void *) tv_dst, (const void *) tv_src, (size_t) count * sizeof(duk_tval));

	/* Overwrite result array to final value stack location and wipe
	 * the rest; no refcount operations needed.
	 */

	tv_dst = tv_src;  /* when count == 0, same as tv_src (OK) */
	tv_src = thr->valstack_top - 1;
	DUK_TVAL_SET_TVAL(tv_dst, tv_src);

	/* XXX: internal helper to wipe a value stack segment? */
	tv_curr = tv_dst + 1;
	tv_limit = thr->valstack_top;
	while (tv_curr != tv_limit) {
		/* Wipe policy: keep as 'undefined'. */
		DUK_TVAL_SET_UNDEFINED(tv_curr);
		tv_curr++;
	}
	thr->valstack_top = tv_dst + 1;
}

DUK_INTERNAL duk_idx_t duk_unpack_array_like(duk_hthread *thr, duk_idx_t idx) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);

	tv = duk_require_tval(thr, idx);
	if (DUK_LIKELY(DUK_TVAL_IS_OBJECT(tv))) {
		duk_hobject *h;
		duk_uint32_t len;
		duk_uint32_t i;

		h = DUK_TVAL_GET_OBJECT(tv);
		DUK_ASSERT(h != NULL);
		DUK_UNREF(h);

#if defined(DUK_USE_ARRAY_FASTPATH)  /* close enough */
		if (DUK_LIKELY(DUK_HOBJECT_IS_ARRAY(h) &&
		               ((duk_harray *) h)->length <= DUK_HOBJECT_GET_ASIZE(h))) {
			duk_harray *h_arr;
			duk_tval *tv_src;
			duk_tval *tv_dst;

			h_arr = (duk_harray *) h;
			len = h_arr->length;
			if (DUK_UNLIKELY(len >= 0x80000000UL)) {
				goto fail_over_2g;
			}
			duk_require_stack(thr, (duk_idx_t) len);

			/* The potential allocation in duk_require_stack() may
			 * run a finalizer which modifies the argArray so that
			 * e.g. becomes sparse.  So, we need to recheck that the
			 * array didn't change size and that there's still a
			 * valid backing array part.
			 *
			 * XXX: alternatively, could prevent finalizers for the
			 * duration.
			 */
			if (DUK_UNLIKELY(len != h_arr->length ||
			                 h_arr->length > DUK_HOBJECT_GET_ASIZE((duk_hobject *) h_arr))) {
				goto skip_fast;
			}

			/* Main fast path: arguments array is almost always
			 * an actual array (though it might also be an arguments
			 * object).
			 */

			DUK_DDD(DUK_DDDPRINT("fast path for %ld elements", (long) h_arr->length));
			tv_src = DUK_HOBJECT_A_GET_BASE(thr->heap, h);
			tv_dst = thr->valstack_top;
			while (len-- > 0) {
				DUK_ASSERT(tv_dst < thr->valstack_end);
				if (DUK_UNLIKELY(DUK_TVAL_IS_UNUSED(tv_src))) {
					/* Gaps are very unlikely.  Skip over them,
					 * without an ancestor lookup (technically
					 * not compliant).
					 */
					DUK_ASSERT(DUK_TVAL_IS_UNDEFINED(tv_dst));  /* valstack policy */
				} else {
					DUK_TVAL_SET_TVAL(tv_dst, tv_src);
					DUK_TVAL_INCREF(thr, tv_dst);
				}
				tv_src++;
				tv_dst++;
			}
			DUK_ASSERT(tv_dst <= thr->valstack_end);
			thr->valstack_top = tv_dst;
			return (duk_idx_t) h_arr->length;
		}
	 skip_fast:
#endif  /* DUK_USE_ARRAY_FASTPATH */

		/* Slow path: actual lookups.  The initial 'length' lookup
		 * decides the output length, regardless of side effects that
		 * may resize or change the argArray while we read the
		 * indices.
		 */
		idx = duk_normalize_index(thr, idx);
		duk_get_prop_stridx(thr, idx, DUK_STRIDX_LENGTH);
		len = duk_to_uint32(thr, -1);  /* ToUint32() coercion required */
		if (DUK_UNLIKELY(len >= 0x80000000UL)) {
			goto fail_over_2g;
		}
		duk_pop_unsafe(thr);
		DUK_DDD(DUK_DDDPRINT("slow path for %ld elements", (long) len));

		duk_require_stack(thr, (duk_idx_t) len);
		for (i = 0; i < len; i++) {
			duk_get_prop_index(thr, idx, (duk_uarridx_t) i);
		}
		return (duk_idx_t) len;
	} else if (DUK_TVAL_IS_UNDEFINED(tv) || DUK_TVAL_IS_NULL(tv)) {
		return 0;
	}

	DUK_ERROR_TYPE_INVALID_ARGS(thr);
	DUK_WO_NORETURN(return 0;);

 fail_over_2g:
	DUK_ERROR_RANGE_INVALID_LENGTH(thr);
	DUK_WO_NORETURN(return 0;);
}

/*
 *  Error throwing
 */

#if defined(DUK_USE_GCC_PRAGMAS)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsuggest-attribute=noreturn"
#elif defined(DUK_USE_CLANG_PRAGMAS)
#pragma clang diagnostic push
#endif

DUK_EXTERNAL void duk_throw_raw(duk_hthread *thr) {
	duk_tval *tv_val;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr->valstack_bottom >= thr->valstack);
	DUK_ASSERT(thr->valstack_top >= thr->valstack_bottom);
	DUK_ASSERT(thr->valstack_end >= thr->valstack_top);

	if (DUK_UNLIKELY(thr->valstack_top == thr->valstack_bottom)) {
		DUK_ERROR_TYPE_INVALID_ARGS(thr);
		DUK_WO_NORETURN(return;);
	}

	/* Errors are augmented when they are created, not when they are
	 * thrown or re-thrown.  The current error handler, however, runs
	 * just before an error is thrown.
	 */

	/* Sync so that augmentation sees up-to-date activations, NULL
	 * thr->ptr_curr_pc so that it's not used if side effects occur
	 * in augmentation or longjmp handling.
	 */
	duk_hthread_sync_and_null_currpc(thr);

#if defined(DUK_USE_AUGMENT_ERROR_THROW)
	DUK_DDD(DUK_DDDPRINT("THROW ERROR (API): %!dT (before throw augment)", (duk_tval *) duk_get_tval(thr, -1)));
	duk_err_augment_error_throw(thr);
#endif
	DUK_DDD(DUK_DDDPRINT("THROW ERROR (API): %!dT (after throw augment)", (duk_tval *) duk_get_tval(thr, -1)));

	tv_val = DUK_GET_TVAL_NEGIDX(thr, -1);
	duk_err_setup_ljstate1(thr, DUK_LJ_TYPE_THROW, tv_val);
#if defined(DUK_USE_DEBUGGER_SUPPORT)
	duk_err_check_debugger_integration(thr);
#endif

	/* thr->heap->lj.jmpbuf_ptr is checked by duk_err_longjmp() so we don't
	 * need to check that here.  If the value is NULL, a fatal error occurs
	 * because we can't return.
	 */

	duk_err_longjmp(thr);
	DUK_UNREACHABLE();
}

DUK_EXTERNAL void duk_fatal_raw(duk_hthread *thr, const char *err_msg) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(thr != NULL);
	DUK_ASSERT(thr->heap != NULL);
	DUK_ASSERT(thr->heap->fatal_func != NULL);

	DUK_D(DUK_DPRINT("fatal error occurred: %s", err_msg ? err_msg : "NULL"));

	/* fatal_func should be noreturn, but noreturn declarations on function
	 * pointers has a very spotty support apparently so it's not currently
	 * done.
	 */
	thr->heap->fatal_func(thr->heap->heap_udata, err_msg);

	/* If the fatal handler returns, all bets are off.  It'd be nice to
	 * print something here but since we don't want to depend on stdio,
	 * there's no way to do so portably.
	 */
	DUK_D(DUK_DPRINT("fatal error handler returned, all bets are off!"));
	for (;;) {
		/* loop forever, don't return (function marked noreturn) */
	}
}

DUK_EXTERNAL void duk_error_va_raw(duk_hthread *thr, duk_errcode_t err_code, const char *filename, duk_int_t line, const char *fmt, va_list ap) {
	DUK_ASSERT_API_ENTRY(thr);

	duk_push_error_object_va_raw(thr, err_code, filename, line, fmt, ap);
	(void) duk_throw(thr);
	DUK_WO_NORETURN(return;);
}

DUK_EXTERNAL void duk_error_raw(duk_hthread *thr, duk_errcode_t err_code, const char *filename, duk_int_t line, const char *fmt, ...) {
	va_list ap;

	DUK_ASSERT_API_ENTRY(thr);

	va_start(ap, fmt);
	duk_push_error_object_va_raw(thr, err_code, filename, line, fmt, ap);
	va_end(ap);
	(void) duk_throw(thr);
	DUK_WO_NORETURN(return;);
}

#if defined(DUK_USE_GCC_PRAGMAS)
#pragma GCC diagnostic pop
#elif defined(DUK_USE_CLANG_PRAGMAS)
#pragma clang diagnostic pop
#endif

#if !defined(DUK_USE_VARIADIC_MACROS)
DUK_NORETURN(DUK_LOCAL_DECL void duk__throw_error_from_stash(duk_hthread *thr, duk_errcode_t err_code, const char *fmt, va_list ap));

DUK_LOCAL void duk__throw_error_from_stash(duk_hthread *thr, duk_errcode_t err_code, const char *fmt, va_list ap) {
	const char *filename;
	duk_int_t line;

	DUK_CTX_ASSERT_VALID(thr);

	filename = duk_api_global_filename;
	line = duk_api_global_line;
	duk_api_global_filename = NULL;
	duk_api_global_line = 0;

	duk_push_error_object_va_raw(thr, err_code, filename, line, fmt, ap);
	(void) duk_throw(thr);
	DUK_WO_NORETURN(return;);
}

#define DUK__ERROR_STASH_SHARED(code) do { \
		va_list ap; \
		va_start(ap, fmt); \
		duk__throw_error_from_stash(thr, (code), fmt, ap); \
		va_end(ap); \
		DUK_WO_NORETURN(return 0;); \
	} while (0)

DUK_EXTERNAL duk_ret_t duk_error_stash(duk_hthread *thr, duk_errcode_t err_code, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(err_code);
}
DUK_EXTERNAL duk_ret_t duk_generic_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_ERROR);
}
DUK_EXTERNAL duk_ret_t duk_eval_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_EVAL_ERROR);
}
DUK_EXTERNAL duk_ret_t duk_range_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_RANGE_ERROR);
}
DUK_EXTERNAL duk_ret_t duk_reference_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_REFERENCE_ERROR);
}
DUK_EXTERNAL duk_ret_t duk_syntax_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_SYNTAX_ERROR);
}
DUK_EXTERNAL duk_ret_t duk_type_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_TYPE_ERROR);
}
DUK_EXTERNAL duk_ret_t duk_uri_error_stash(duk_hthread *thr, const char *fmt, ...) {
	DUK_ASSERT_API_ENTRY(thr);
	DUK__ERROR_STASH_SHARED(DUK_ERR_URI_ERROR);
}
#endif  /* DUK_USE_VARIADIC_MACROS */

/*
 *  Comparison
 */

DUK_EXTERNAL duk_bool_t duk_equals(duk_hthread *thr, duk_idx_t idx1, duk_idx_t idx2) {
	duk_tval *tv1, *tv2;

	DUK_ASSERT_API_ENTRY(thr);

	tv1 = duk_get_tval(thr, idx1);
	tv2 = duk_get_tval(thr, idx2);
	if ((tv1 == NULL) || (tv2 == NULL)) {
		return 0;
	}

	/* Coercion may be needed, the helper handles that by pushing the
	 * tagged values to the stack.
	 */
	return duk_js_equals(thr, tv1, tv2);
}

DUK_EXTERNAL duk_bool_t duk_strict_equals(duk_hthread *thr, duk_idx_t idx1, duk_idx_t idx2) {
	duk_tval *tv1, *tv2;

	DUK_ASSERT_API_ENTRY(thr);

	tv1 = duk_get_tval(thr, idx1);
	tv2 = duk_get_tval(thr, idx2);
	if ((tv1 == NULL) || (tv2 == NULL)) {
		return 0;
	}

	/* No coercions or other side effects, so safe */
	return duk_js_strict_equals(tv1, tv2);
}

DUK_EXTERNAL duk_bool_t duk_samevalue(duk_hthread *thr, duk_idx_t idx1, duk_idx_t idx2) {
	duk_tval *tv1, *tv2;

	DUK_ASSERT_API_ENTRY(thr);

	tv1 = duk_get_tval(thr, idx1);
	tv2 = duk_get_tval(thr, idx2);
	if ((tv1 == NULL) || (tv2 == NULL)) {
		return 0;
	}

	/* No coercions or other side effects, so safe */
	return duk_js_samevalue(tv1, tv2);
}

/*
 *  instanceof
 */

DUK_EXTERNAL duk_bool_t duk_instanceof(duk_hthread *thr, duk_idx_t idx1, duk_idx_t idx2) {
	duk_tval *tv1, *tv2;

	DUK_ASSERT_API_ENTRY(thr);

	/* Index validation is strict, which differs from duk_equals().
	 * The strict behavior mimics how instanceof itself works, e.g.
	 * it is a TypeError if rval is not a -callable- object.  It would
	 * be somewhat inconsistent if rval would be allowed to be
	 * non-existent without a TypeError.
	 */
	tv1 = duk_require_tval(thr, idx1);
	DUK_ASSERT(tv1 != NULL);
	tv2 = duk_require_tval(thr, idx2);
	DUK_ASSERT(tv2 != NULL);

	return duk_js_instanceof(thr, tv1, tv2);
}

/*
 *  Lightfunc
 */

DUK_INTERNAL void duk_push_lightfunc_name_raw(duk_hthread *thr, duk_c_function func, duk_small_uint_t lf_flags) {
	/* Lightfunc name, includes Duktape/C native function pointer, which
	 * can often be used to locate the function from a symbol table.
	 * The name also includes the 16-bit duk_tval flags field because it
	 * includes the magic value.  Because a single native function often
	 * provides different functionality depending on the magic value, it
	 * seems reasonably to include it in the name.
	 *
	 * On the other hand, a complicated name increases string table
	 * pressure in low memory environments (but only when function name
	 * is accessed).
	 */

	DUK_ASSERT_API_ENTRY(thr);

	duk_push_literal(thr, "light_");
	duk_push_string_funcptr(thr, (duk_uint8_t *) &func, sizeof(func));
	duk_push_sprintf(thr, "_%04x", (unsigned int) lf_flags);
	duk_concat(thr, 3);
}

DUK_INTERNAL void duk_push_lightfunc_name(duk_hthread *thr, duk_tval *tv) {
	duk_c_function func;
	duk_small_uint_t lf_flags;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_TVAL_IS_LIGHTFUNC(tv));

	DUK_TVAL_GET_LIGHTFUNC(tv, func, lf_flags);
	duk_push_lightfunc_name_raw(thr, func, lf_flags);
}

DUK_INTERNAL void duk_push_lightfunc_tostring(duk_hthread *thr, duk_tval *tv) {
	duk_c_function func;
	duk_small_uint_t lf_flags;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(DUK_TVAL_IS_LIGHTFUNC(tv));

	DUK_TVAL_GET_LIGHTFUNC(tv, func, lf_flags);  /* read before 'tv' potentially invalidated */
	duk_push_literal(thr, "function ");
	duk_push_lightfunc_name_raw(thr, func, lf_flags);
	duk_push_literal(thr, "() { [lightfunc code] }");
	duk_concat(thr, 3);
}

/*
 *  Function pointers
 *
 *  Printing function pointers is non-portable, so we do that by hex printing
 *  bytes from memory.
 */

DUK_INTERNAL void duk_push_string_funcptr(duk_hthread *thr, duk_uint8_t *ptr, duk_size_t sz) {
	duk_uint8_t buf[32 * 2];
	duk_uint8_t *p, *q;
	duk_small_uint_t i;
	duk_small_uint_t t;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(sz <= 32);  /* sanity limit for function pointer size */

	p = buf;
#if defined(DUK_USE_INTEGER_LE)
	q = ptr + sz;
#else
	q = ptr;
#endif
	for (i = 0; i < sz; i++) {
#if defined(DUK_USE_INTEGER_LE)
		t = *(--q);
#else
		t = *(q++);
#endif
		*p++ = duk_lc_digits[t >> 4];
		*p++ = duk_lc_digits[t & 0x0f];
	}

	duk_push_lstring(thr, (const char *) buf, sz * 2);
}

/*
 *  Push readable string summarizing duk_tval.  The operation is side effect
 *  free and will only throw from internal errors (e.g. out of memory).
 *  This is used by e.g. property access code to summarize a key/base safely,
 *  and is not intended to be fast (but small and safe).
 */

/* String limits for summary strings. */
#define DUK__READABLE_SUMMARY_MAXCHARS 96  /* maximum supported by helper */
#define DUK__READABLE_STRING_MAXCHARS  32  /* for strings/symbols */
#define DUK__READABLE_ERRMSG_MAXCHARS  96  /* for error messages */

/* String sanitizer which escapes ASCII control characters and a few other
 * ASCII characters, passes Unicode as is, and replaces invalid UTF-8 with
 * question marks.  No errors are thrown for any input string, except in out
 * of memory situations.
 */
DUK_LOCAL void duk__push_hstring_readable_unicode(duk_hthread *thr, duk_hstring *h_input, duk_small_uint_t maxchars) {
	const duk_uint8_t *p, *p_start, *p_end;
	duk_uint8_t buf[DUK_UNICODE_MAX_XUTF8_LENGTH * DUK__READABLE_SUMMARY_MAXCHARS +
	                2 /*quotes*/ + 3 /*periods*/];
	duk_uint8_t *q;
	duk_ucodepoint_t cp;
	duk_small_uint_t nchars;

	DUK_CTX_ASSERT_VALID(thr);
	DUK_ASSERT(h_input != NULL);
	DUK_ASSERT(maxchars <= DUK__READABLE_SUMMARY_MAXCHARS);

	p_start = (const duk_uint8_t *) DUK_HSTRING_GET_DATA(h_input);
	p_end = p_start + DUK_HSTRING_GET_BYTELEN(h_input);
	p = p_start;
	q = buf;

	nchars = 0;
	*q++ = (duk_uint8_t) DUK_ASC_SINGLEQUOTE;
	for (;;) {
		if (p >= p_end) {
			break;
		}
		if (nchars == maxchars) {
			*q++ = (duk_uint8_t) DUK_ASC_PERIOD;
			*q++ = (duk_uint8_t) DUK_ASC_PERIOD;
			*q++ = (duk_uint8_t) DUK_ASC_PERIOD;
			break;
		}
		if (duk_unicode_decode_xutf8(thr, &p, p_start, p_end, &cp)) {
			if (cp < 0x20 || cp == 0x7f || cp == DUK_ASC_SINGLEQUOTE || cp == DUK_ASC_BACKSLASH) {
				DUK_ASSERT(DUK_UNICODE_MAX_XUTF8_LENGTH >= 4);  /* estimate is valid */
				DUK_ASSERT((cp >> 4) <= 0x0f);
				*q++ = (duk_uint8_t) DUK_ASC_BACKSLASH;
				*q++ = (duk_uint8_t) DUK_ASC_LC_X;
				*q++ = (duk_uint8_t) duk_lc_digits[cp >> 4];
				*q++ = (duk_uint8_t) duk_lc_digits[cp & 0x0f];
			} else {
				q += duk_unicode_encode_xutf8(cp, q);
			}
		} else {
			p++;  /* advance manually */
			*q++ = (duk_uint8_t) DUK_ASC_QUESTION;
		}
		nchars++;
	}
	*q++ = (duk_uint8_t) DUK_ASC_SINGLEQUOTE;

	duk_push_lstring(thr, (const char *) buf, (duk_size_t) (q - buf));
}

DUK_LOCAL const char *duk__push_string_tval_readable(duk_hthread *thr, duk_tval *tv, duk_bool_t error_aware) {
	DUK_CTX_ASSERT_VALID(thr);
	/* 'tv' may be NULL */

	if (tv == NULL) {
		duk_push_literal(thr, "none");
	} else {
		switch (DUK_TVAL_GET_TAG(tv)) {
		case DUK_TAG_STRING: {
			duk_hstring *h = DUK_TVAL_GET_STRING(tv);
			if (DUK_HSTRING_HAS_SYMBOL(h)) {
				/* XXX: string summary produces question marks
				 * so this is not very ideal.
				 */
				duk_push_literal(thr, "[Symbol ");
				duk_push_string(thr, duk__get_symbol_type_string(h));
				duk_push_literal(thr, " ");
				duk__push_hstring_readable_unicode(thr, h, DUK__READABLE_STRING_MAXCHARS);
				duk_push_literal(thr, "]");
				duk_concat(thr, 5);
				break;
			}
			duk__push_hstring_readable_unicode(thr, h, DUK__READABLE_STRING_MAXCHARS);
			break;
		}
		case DUK_TAG_OBJECT: {
			duk_hobject *h = DUK_TVAL_GET_OBJECT(tv);
			DUK_ASSERT(h != NULL);

			if (error_aware &&
			    duk_hobject_prototype_chain_contains(thr, h, thr->builtins[DUK_BIDX_ERROR_PROTOTYPE], 1 /*ignore_loop*/)) {
				/* Get error message in a side effect free way if
				 * possible; if not, summarize as a generic object.
				 * Error message currently gets quoted.
				 */
				/* XXX: better internal getprop call; get without side effects
				 * but traverse inheritance chain.
				 */
				duk_tval *tv_msg;
				tv_msg = duk_hobject_find_entry_tval_ptr_stridx(thr->heap, h, DUK_STRIDX_MESSAGE);
				if (tv_msg != NULL && DUK_TVAL_IS_STRING(tv_msg)) {
					/* It's critical to avoid recursion so
					 * only summarize a string .message.
					 */
					duk__push_hstring_readable_unicode(thr, DUK_TVAL_GET_STRING(tv_msg), DUK__READABLE_ERRMSG_MAXCHARS);
					break;
				}
			}
			duk_push_class_string_tval(thr, tv, 1 /*avoid_side_effects*/);
			break;
		}
		case DUK_TAG_BUFFER: {
			/* While plain buffers mimic Uint8Arrays, they summarize differently.
			 * This is useful so that the summarized string accurately reflects the
			 * internal type which may matter for figuring out bugs etc.
			 */
			/* XXX: Hex encoded, length limited buffer summary here? */
			duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
			DUK_ASSERT(h != NULL);
			duk_push_sprintf(thr, "[buffer:%ld]", (long) DUK_HBUFFER_GET_SIZE(h));
			break;
		}
		case DUK_TAG_POINTER: {
			/* Surround with parentheses like in JX, ensures NULL pointer
			 * is distinguishable from null value ("(null)" vs "null").
			 */
			duk_push_tval(thr, tv);
			duk_push_sprintf(thr, "(%s)", duk_to_string(thr, -1));
			duk_remove_m2(thr);
			break;
		}
		default: {
			duk_push_tval(thr, tv);
			break;
		}
		}
	}

	return duk_to_string(thr, -1);
}
DUK_INTERNAL const char *duk_push_string_tval_readable(duk_hthread *thr, duk_tval *tv) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__push_string_tval_readable(thr, tv, 0 /*error_aware*/);
}

DUK_INTERNAL const char *duk_push_string_readable(duk_hthread *thr, duk_idx_t idx) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk_push_string_tval_readable(thr, duk_get_tval(thr, idx));
}

DUK_INTERNAL const char *duk_push_string_tval_readable_error(duk_hthread *thr, duk_tval *tv) {
	DUK_ASSERT_API_ENTRY(thr);
	return duk__push_string_tval_readable(thr, tv, 1 /*error_aware*/);
}

DUK_INTERNAL void duk_push_symbol_descriptive_string(duk_hthread *thr, duk_hstring *h) {
	const duk_uint8_t *p;
	const duk_uint8_t *p_end;
	const duk_uint8_t *q;

	DUK_ASSERT_API_ENTRY(thr);

	/* .toString() */
	duk_push_literal(thr, "Symbol(");
	p = (const duk_uint8_t *) DUK_HSTRING_GET_DATA(h);
	p_end = p + DUK_HSTRING_GET_BYTELEN(h);
	DUK_ASSERT(p[0] == 0xff || (p[0] & 0xc0) == 0x80);
	p++;
	for (q = p; q < p_end; q++) {
		if (*q == 0xffU) {
			/* Terminate either at end-of-string (but NUL MUST
			 * be accepted without terminating description) or
			 * 0xFF, which is used to mark start of unique trailer
			 * (and cannot occur in CESU-8 / extended UTF-8).
			 */
			break;
		}
	}
	duk_push_lstring(thr, (const char *) p, (duk_size_t) (q - p));
	duk_push_literal(thr, ")");
	duk_concat(thr, 3);
}

/*
 *  Functions
 */

#if 0  /* not used yet */
DUK_INTERNAL void duk_push_hnatfunc_name(duk_hthread *thr, duk_hnatfunc *h) {
	duk_c_function func;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_ASSERT(h != NULL);
	DUK_ASSERT(DUK_HOBJECT_IS_NATFUNC((duk_hobject *) h));

	duk_push_sprintf(thr, "native_");
	func = h->func;
	duk_push_string_funcptr(thr, (duk_uint8_t *) &func, sizeof(func));
	duk_push_sprintf(thr, "_%04x_%04x",
	                 (unsigned int) (duk_uint16_t) h->nargs,
	                 (unsigned int) (duk_uint16_t) h->magic);
	duk_concat(thr, 3);
}
#endif

/*
 *  duk_tval slice copy
 */

DUK_INTERNAL void duk_copy_tvals_incref(duk_hthread *thr, duk_tval *tv_dst, duk_tval *tv_src, duk_size_t count) {
	duk_tval *tv;

	DUK_ASSERT_API_ENTRY(thr);
	DUK_UNREF(thr);
	DUK_ASSERT(count * sizeof(duk_tval) >= count);  /* no wrap */

	duk_memcpy_unsafe((void *) tv_dst, (const void *) tv_src, count * sizeof(duk_tval));

	tv = tv_dst;
	while (count-- > 0) {
		DUK_TVAL_INCREF(thr, tv);
		tv++;
	}
}