blender-archive/source/blender/blenlib/intern/hash_mm2a.c

/*
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * ***** END GPL LICENSE BLOCK *****
 *
 * Copyright (C) 2014 Blender Foundation.
 *
 */

/** \file blender/blenlib/intern/hash_mm2a.c
 *  \ingroup bli
 *
 *  Functions to compute Murmur2A hash key.
 *
 * A very fast hash generating int32 result, with few collisions and good repartition.
 *
 * See also:
 *     reference implementation: https://smhasher.googlecode.com/svn-history/r130/trunk/MurmurHash2.cpp
 *     and http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed
 *
 * \warning Do not store that hash in files or such, it is not endian-agnostic, so you should only use it
 *          for temporary data.
 */

#include "BLI_hash_mm2a.h"  /* own include */

/* Helpers. */
#define MM2A_M 0x5bd1e995

#define MM2A_MIX(h, k)           \
{                                \
	(k) *= MM2A_M;               \
	(k) ^= (k) >> 24;            \
	(k) *= MM2A_M;               \
	(h) = ((h) * MM2A_M) ^ (k);  \
} (void)0

static void mm2a_mix_tail(BLI_HashMurmur2A *mm2, const unsigned char **data, size_t *len)
{
	while (*len && ((*len < 4) || mm2->count)) {
		mm2->tail |= (uint32_t)(**data) << (mm2->count * 8);

		mm2->count++;
		(*len)--;
		(*data)++;

		if (mm2->count == 4) {
			MM2A_MIX(mm2->hash, mm2->tail);
			mm2->tail = 0;
			mm2->count = 0;
		}
	}
}

void BLI_hash_mm2a_init(BLI_HashMurmur2A *mm2, uint32_t seed)
{
	mm2->hash  = seed;
	mm2->tail  = 0;
	mm2->count = 0;
	mm2->size  = 0;
}

void BLI_hash_mm2a_add(BLI_HashMurmur2A *mm2, const unsigned char *data, size_t len)
{
	mm2->size += (uint32_t)len;

	mm2a_mix_tail(mm2, &data, &len);

	for (; len >= 4; data += 4, len -= 4) {
		uint32_t k = *(uint32_t *)data;

		MM2A_MIX(mm2->hash, k);
	}

	mm2a_mix_tail(mm2, &data, &len);
}

void BLI_hash_mm2a_add_int(BLI_HashMurmur2A *mm2, int data)
{
	BLI_hash_mm2a_add(mm2, (const unsigned char *)&data, sizeof(data));
}

uint32_t BLI_hash_mm2a_end(BLI_HashMurmur2A *mm2)
{
	MM2A_MIX(mm2->hash, mm2->tail);
	MM2A_MIX(mm2->hash, mm2->size);

	mm2->hash ^= mm2->hash >> 13;
	mm2->hash *= MM2A_M;
	mm2->hash ^= mm2->hash >> 15;

	return mm2->hash;
}