130 lines
2.7 KiB
C++
130 lines
2.7 KiB
C++
/* SPDX-FileCopyrightText: 2014 Blender Authors
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*
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* SPDX-License-Identifier: GPL-2.0-or-later */
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/** \file
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* \ingroup bli
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*
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* Functions to compute Murmur2A hash key.
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*
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* A very fast hash generating int32 result, with few collisions and good repartition.
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*
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* See also:
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* reference implementation:
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* - https://smhasher.googlecode.com/svn-history/r130/trunk/MurmurHash2.cpp
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* - http://programmers.stackexchange.com/questions/49550
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*
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* \warning Do not store that hash in files or such, it is not endian-agnostic,
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* so you should only use it for temporary data.
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*/
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#include "BLI_compiler_attrs.h"
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#include "BLI_hash_mm2a.hh" /* own include */
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/* Helpers. */
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#define MM2A_M 0x5bd1e995
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#define MM2A_MIX(h, k) \
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{ \
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(k) *= MM2A_M; \
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(k) ^= (k) >> 24; \
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(k) *= MM2A_M; \
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(h) = ((h) * MM2A_M) ^ (k); \
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} \
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(void)0
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#define MM2A_MIX_FINALIZE(h) \
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{ \
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(h) ^= (h) >> 13; \
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(h) *= MM2A_M; \
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(h) ^= (h) >> 15; \
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} \
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(void)0
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static void mm2a_mix_tail(BLI_HashMurmur2A *mm2, const uchar **data, size_t *len)
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{
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while (*len && ((*len < 4) || mm2->count)) {
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mm2->tail |= uint32_t(**data) << (mm2->count * 8);
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mm2->count++;
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(*len)--;
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(*data)++;
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if (mm2->count == 4) {
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MM2A_MIX(mm2->hash, mm2->tail);
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mm2->tail = 0;
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mm2->count = 0;
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}
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}
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}
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void BLI_hash_mm2a_init(BLI_HashMurmur2A *mm2, uint32_t seed)
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{
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mm2->hash = seed;
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mm2->tail = 0;
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mm2->count = 0;
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mm2->size = 0;
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}
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void BLI_hash_mm2a_add(BLI_HashMurmur2A *mm2, const uchar *data, size_t len)
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{
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mm2->size += uint32_t(len);
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mm2a_mix_tail(mm2, &data, &len);
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for (; len >= 4; data += 4, len -= 4) {
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uint32_t k = *(const uint32_t *)data;
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MM2A_MIX(mm2->hash, k);
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}
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mm2a_mix_tail(mm2, &data, &len);
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}
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void BLI_hash_mm2a_add_int(BLI_HashMurmur2A *mm2, int data)
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{
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BLI_hash_mm2a_add(mm2, (const uchar *)&data, sizeof(data));
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}
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uint32_t BLI_hash_mm2a_end(BLI_HashMurmur2A *mm2)
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{
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MM2A_MIX(mm2->hash, mm2->tail);
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MM2A_MIX(mm2->hash, mm2->size);
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MM2A_MIX_FINALIZE(mm2->hash);
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return mm2->hash;
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}
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uint32_t BLI_hash_mm2(const uchar *data, size_t len, uint32_t seed)
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{
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/* Initialize the hash to a 'random' value */
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uint32_t h = seed ^ len;
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/* Mix 4 bytes at a time into the hash */
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for (; len >= 4; data += 4, len -= 4) {
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uint32_t k = *(uint32_t *)data;
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MM2A_MIX(h, k);
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}
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/* Handle the last few bytes of the input array */
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switch (len) {
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case 3:
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h ^= data[2] << 16;
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ATTR_FALLTHROUGH;
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case 2:
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h ^= data[1] << 8;
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ATTR_FALLTHROUGH;
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case 1:
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h ^= data[0];
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h *= MM2A_M;
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}
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/* Do a few final mixes of the hash to ensure the last few bytes are well-incorporated. */
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MM2A_MIX_FINALIZE(h);
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return h;
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}
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