35 lines
1.4 KiB
YAML
35 lines
1.4 KiB
YAML
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define: DUK_OPT_HEAPPTR16
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introduced: 1.1.0
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conflicts:
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- DUK_OPT_DEBUG
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related:
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- DUK_OPT_HEAPPTR_ENC16
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- DUK_OPT_HEAPPTR_DEC16
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tags:
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- lowmemory
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- experimental
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description: >
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Enable "compression" of Duktape heap pointers into an unsigned 16-bit value.
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Use together with DUK_OPT_HEAPPTR_ENC16 and DUK_OPT_HEAPPTR_DEC16.
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Pointers compressed are those allocated from Duktape heap, using the user
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provided allocation functions. Also NULL pointer must encode and decode
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correctly.
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Currently it is required that NULL encodes to integer 0, and integer
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0 decodes to NULL. No other pointer can be encoded to 0.
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This option reduces memory usage by several kilobytes, but has several
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downsides. It can only be applied when Duktape heap is limited in size,
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for instance, with 4-byte aligned allocations a 256kB heap (minus one value
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for NULL) can be supported. Pointer encoding and decoding may be relatively
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complicated as they need to correctly handle NULL pointers and
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non-continuous memory maps used by some targets. The macro may need to call
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out to a helper function in practice, which is much slower than an inline
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implementation.
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Current limitation: Duktape internal debug code enabled with e.g.
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DUK_OPT_DEBUG and DUK_OPT_DPRINT doesn't have enough plumbing to be able to
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decode pointers. Debug printing cannot currently be enabled when pointer
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compression is active.
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