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/*
* virhashcode.c: hash code generation
*
* Copyright (C) 2012 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see
* <http://www.gnu.org/licenses/>.
*
* The hash code generation is based on the public domain MurmurHash3 from Austin Appleby:
* https://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
*
* We use only the 32 bit variant because the 2 produce different results while
* we need to produce the same result regardless of the architecture as
* clients can be both 64 or 32 bit at the same time.
*/
#include <config.h>
#include "virhashcode.h"
static uint32_t rotl32(uint32_t x, int8_t r)
{
return (x << r) | (x >> (32 - r));
}
/* slower than original but handles platforms that do only aligned reads */
static inline uint32_t getblock(const uint8_t *p, int i)
{
uint32_t r;
size_t size = sizeof(r);
memcpy(&r, &p[i * size], size);
return r;
}
/*
* Finalization mix - force all bits of a hash block to avalanche
*/
static inline uint32_t fmix(uint32_t h)
{
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
h ^= h >> 16;
return h;
}
uint32_t virHashCodeGen(const void *key, size_t len, uint32_t seed)
{
const uint8_t *blocks;
const uint8_t *tail;
size_t nblocks;
uint32_t h1;
uint32_t k1;
uint32_t c1;
uint32_t c2;
size_t i;
blocks = (const uint8_t *)key;
nblocks = len / 4;
h1 = seed;
c1 = 0xcc9e2d51;
c2 = 0x1b873593;
/* body */
for (i = 0; i < nblocks; i++) {
k1 = getblock(blocks, i);
k1 *= c1;
k1 = rotl32(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = rotl32(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}
/* tail */
tail = (const uint8_t *)key + nblocks * 4;
k1 = 0;
switch (len & 3) {
case 3:
k1 ^= tail[2] << 16;
G_GNUC_FALLTHROUGH;
case 2:
k1 ^= tail[1] << 8;
G_GNUC_FALLTHROUGH;
case 1:
k1 ^= tail[0];
k1 *= c1;
k1 = rotl32(k1, 15);
k1 *= c2;
h1 ^= k1;
G_GNUC_FALLTHROUGH;
default:
break;
}
/* finalization */
h1 ^= len;
h1 = fmix(h1);
return h1;
}
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