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/* This file is based on the public domain MurmurHash3 from Austin Appleby:
* http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
*
* We use only the 32 bit variant because the 2 produce different result 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 <stdlib.h>
#include <stdint.h>
#include <endian.h>
#include <string.h>
/* support RHEL5 lack of definitions */
#ifndef le32toh
# if __BYTE_ORDER == __LITTLE_ENDIAN
# define le32toh(x) (x)
# else
# define le32toh(x) __bswap_32 (x)
# endif
#endif
static uint32_t rotl(uint32_t x, int8_t r)
{
return (x << r) | (x >> (32 - r));
}
/* slower than original but is endian neutral and handles platforms that
* do only aligned reads */
__attribute__((always_inline))
static uint32_t getblock(const uint8_t *p, int i)
{
uint32_t r;
size_t size = sizeof(uint32_t);
memcpy(&r, &p[i * size], size);
return le32toh(r);
}
/*
* Finalization mix - force all bits of a hash block to avalanche
*/
__attribute__((always_inline))
static uint32_t fmix(uint32_t h)
{
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
h ^= h >> 16;
return h;
}
uint32_t murmurhash3(const char *key, int len, uint32_t seed)
{
const uint8_t *blocks;
const uint8_t *tail;
int nblocks;
uint32_t h1;
uint32_t k1;
uint32_t c1;
uint32_t c2;
int 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 = rotl(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = rotl(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;
case 2:
k1 ^= tail[1] << 8;
case 1:
k1 ^= tail[0];
k1 *= c1;
k1 = rotl(k1, 15);
k1 *= c2;
h1 ^= k1;
default:
break;
}
/* finalization */
h1 ^= len;
h1 = fmix(h1);
return h1;
}
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