57 lines
1.5 KiB
C
57 lines
1.5 KiB
C
/*
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* Hash function duk_util_hashbytes().
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*
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* Currently, 32-bit MurmurHash2.
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*
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* Don't rely on specific hash values; hash function may be endianness
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* dependent, for instance.
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*/
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#include "duk_internal.h"
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#if defined(DUK_USE_STRHASH_DENSE)
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/* 'magic' constants for Murmurhash2 */
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#define DUK__MAGIC_M ((duk_uint32_t) 0x5bd1e995UL)
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#define DUK__MAGIC_R 24
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DUK_INTERNAL duk_uint32_t duk_util_hashbytes(const duk_uint8_t *data, duk_size_t len, duk_uint32_t seed) {
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duk_uint32_t h = seed ^ ((duk_uint32_t) len);
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while (len >= 4) {
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/* Portability workaround is required for platforms without
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* unaligned access. The replacement code emulates little
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* endian access even on big endian architectures, which is
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* OK as long as it is consistent for a build.
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*/
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#if defined(DUK_USE_HASHBYTES_UNALIGNED_U32_ACCESS)
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duk_uint32_t k = *((const duk_uint32_t *) (const void *) data);
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#else
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duk_uint32_t k = ((duk_uint32_t) data[0]) |
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(((duk_uint32_t) data[1]) << 8) |
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(((duk_uint32_t) data[2]) << 16) |
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(((duk_uint32_t) data[3]) << 24);
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#endif
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k *= DUK__MAGIC_M;
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k ^= k >> DUK__MAGIC_R;
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k *= DUK__MAGIC_M;
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h *= DUK__MAGIC_M;
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h ^= k;
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data += 4;
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len -= 4;
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}
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switch (len) {
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case 3: h ^= data[2] << 16;
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case 2: h ^= data[1] << 8;
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case 1: h ^= data[0];
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h *= DUK__MAGIC_M;
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}
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h ^= h >> 13;
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h *= DUK__MAGIC_M;
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h ^= h >> 15;
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return h;
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}
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#endif /* DUK_USE_STRHASH_DENSE */
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