duktape-1.5.2/src-separate/duk_util_hashbytes.c

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