110 lines
5.5 KiB
C
110 lines
5.5 KiB
C
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/*
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* Byte order and double memory layout detection
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*
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* Endianness detection is a major portability hassle because the macros
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* and headers are not standardized. There's even variance across UNIX
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* platforms. Even with "standard" headers, details like underscore count
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* varies between platforms, e.g. both __BYTE_ORDER and _BYTE_ORDER are used
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* (Crossbridge has a single underscore, for instance).
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*
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* The checks below are structured with this in mind: several approaches are
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* used, and at the end we check if any of them worked. This allows generic
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* approaches to be tried first, and platform/compiler specific hacks tried
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* last. As a last resort, the user can force a specific endianness, as it's
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* not likely that automatic detection will work on the most exotic platforms.
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*
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* Duktape supports little and big endian machines. There's also support
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* for a hybrid used by some ARM machines where integers are little endian
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* but IEEE double values use a mixed order (12345678 -> 43218765). This
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* byte order for doubles is referred to as "mixed endian".
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*/
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/* GCC and Clang provide endianness defines as built-in predefines, with
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* leading and trailing double underscores (e.g. __BYTE_ORDER__). See
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* output of "make gccpredefs" and "make clangpredefs". Clang doesn't
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* seem to provide __FLOAT_WORD_ORDER__; assume not mixed endian for clang.
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* http://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html
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*/
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#if !defined(DUK_USE_BYTEORDER) && defined(__BYTE_ORDER__)
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#if defined(__ORDER_LITTLE_ENDIAN__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
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#if defined(__FLOAT_WORD_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && (__FLOAT_WORD_ORDER__ == __ORDER_LITTLE_ENDIAN__)
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#define DUK_USE_BYTEORDER 1
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#elif defined(__FLOAT_WORD_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && (__FLOAT_WORD_ORDER__ == __ORDER_BIG_ENDIAN__)
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#define DUK_USE_BYTEORDER 2
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#elif !defined(__FLOAT_WORD_ORDER__)
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/* Float word order not known, assume not a hybrid. */
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#define DUK_USE_BYTEORDER 1
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#else
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/* Byte order is little endian but cannot determine IEEE double word order. */
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#endif /* float word order */
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#elif defined(__ORDER_BIG_ENDIAN__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
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#if defined(__FLOAT_WORD_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && (__FLOAT_WORD_ORDER__ == __ORDER_BIG_ENDIAN__)
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#define DUK_USE_BYTEORDER 3
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#elif !defined(__FLOAT_WORD_ORDER__)
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/* Float word order not known, assume not a hybrid. */
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#define DUK_USE_BYTEORDER 3
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#else
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/* Byte order is big endian but cannot determine IEEE double word order. */
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#endif /* float word order */
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#else
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/* Cannot determine byte order; __ORDER_PDP_ENDIAN__ is related to 32-bit
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* integer ordering and is not relevant.
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*/
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#endif /* integer byte order */
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#endif /* !defined(DUK_USE_BYTEORDER) && defined(__BYTE_ORDER__) */
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/* More or less standard endianness predefines provided by header files.
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* The ARM hybrid case is detected by assuming that __FLOAT_WORD_ORDER
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* will be big endian, see: http://lists.mysql.com/internals/443.
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* On some platforms some defines may be present with an empty value which
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* causes comparisons to fail: https://github.com/svaarala/duktape/issues/453.
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*/
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#if !defined(DUK_USE_BYTEORDER)
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#if defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && (__BYTE_ORDER == __LITTLE_ENDIAN) || \
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defined(_BYTE_ORDER) && defined(_LITTLE_ENDIAN) && (_BYTE_ORDER == _LITTLE_ENDIAN) || \
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defined(__LITTLE_ENDIAN__)
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#if defined(__FLOAT_WORD_ORDER) && defined(__LITTLE_ENDIAN) && (__FLOAT_WORD_ORDER == __LITTLE_ENDIAN) || \
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defined(_FLOAT_WORD_ORDER) && defined(_LITTLE_ENDIAN) && (_FLOAT_WORD_ORDER == _LITTLE_ENDIAN)
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#define DUK_USE_BYTEORDER 1
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#elif defined(__FLOAT_WORD_ORDER) && defined(__BIG_ENDIAN) && (__FLOAT_WORD_ORDER == __BIG_ENDIAN) || \
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defined(_FLOAT_WORD_ORDER) && defined(_BIG_ENDIAN) && (_FLOAT_WORD_ORDER == _BIG_ENDIAN)
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#define DUK_USE_BYTEORDER 2
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#elif !defined(__FLOAT_WORD_ORDER) && !defined(_FLOAT_WORD_ORDER)
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/* Float word order not known, assume not a hybrid. */
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#define DUK_USE_BYTEORDER 1
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#else
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/* Byte order is little endian but cannot determine IEEE double word order. */
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#endif /* float word order */
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#elif defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && (__BYTE_ORDER == __BIG_ENDIAN) || \
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defined(_BYTE_ORDER) && defined(_BIG_ENDIAN) && (_BYTE_ORDER == _BIG_ENDIAN) || \
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defined(__BIG_ENDIAN__)
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#if defined(__FLOAT_WORD_ORDER) && defined(__BIG_ENDIAN) && (__FLOAT_WORD_ORDER == __BIG_ENDIAN) || \
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defined(_FLOAT_WORD_ORDER) && defined(_BIG_ENDIAN) && (_FLOAT_WORD_ORDER == _BIG_ENDIAN)
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#define DUK_USE_BYTEORDER 3
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#elif !defined(__FLOAT_WORD_ORDER) && !defined(_FLOAT_WORD_ORDER)
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/* Float word order not known, assume not a hybrid. */
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#define DUK_USE_BYTEORDER 3
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#else
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/* Byte order is big endian but cannot determine IEEE double word order. */
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#endif /* float word order */
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#else
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/* Cannot determine byte order. */
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#endif /* integer byte order */
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#endif /* !defined(DUK_USE_BYTEORDER) */
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/* QNX gcc cross compiler seems to define e.g. __LITTLEENDIAN__ or __BIGENDIAN__:
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* $ /opt/qnx650/host/linux/x86/usr/bin/i486-pc-nto-qnx6.5.0-gcc -dM -E - </dev/null | grep -ni endian
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* 67:#define __LITTLEENDIAN__ 1
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* $ /opt/qnx650/host/linux/x86/usr/bin/mips-unknown-nto-qnx6.5.0-gcc -dM -E - </dev/null | grep -ni endian
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* 81:#define __BIGENDIAN__ 1
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* $ /opt/qnx650/host/linux/x86/usr/bin/arm-unknown-nto-qnx6.5.0-gcc -dM -E - </dev/null | grep -ni endian
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* 70:#define __LITTLEENDIAN__ 1
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*/
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#if !defined(DUK_USE_BYTEORDER)
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#if defined(__LITTLEENDIAN__)
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#define DUK_USE_BYTEORDER 1
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#elif defined(__BIGENDIAN__)
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#define DUK_USE_BYTEORDER 3
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#endif
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#endif
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