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/* $NetBSD: murmurhash.c,v 1.6 2013/10/26 21:06:38 rmind Exp $ */
/*
* MurmurHash2 -- from the original code:
*
* "MurmurHash2 was written by Austin Appleby, and is placed in the public
* domain. The author hereby disclaims copyright to this source code."
*
* References:
* http://code.google.com/p/smhasher/
* https://sites.google.com/site/murmurhash/
*/
#include <sys/cdefs.h>
#if defined(_KERNEL) || defined(_STANDALONE)
__KERNEL_RCSID(0, "$NetBSD: murmurhash.c,v 1.6 2013/10/26 21:06:38 rmind Exp $");
#else
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: murmurhash.c,v 1.6 2013/10/26 21:06:38 rmind Exp $");
#endif /* LIBC_SCCS and not lint */
#include "namespace.h"
#endif
#include <sys/types.h>
#include <sys/param.h>
#include <sys/hash.h>
#if !defined(_KERNEL) && !defined(_STANDALONE)
#ifdef __weak_alias
__weak_alias(murmurhash2,_murmurhash2)
#endif
#endif
uint32_t
murmurhash2(const void *key, size_t len, uint32_t seed)
{
/*
* Note: 'm' and 'r' are mixing constants generated offline.
* They're not really 'magic', they just happen to work well.
* Initialize the hash to a 'random' value.
*/
const uint32_t m = 0x5bd1e995;
const int r = 24;
const uint8_t *data = key;
uint32_t h = seed ^ (uint32_t)len;
if (__predict_true(ALIGNED_POINTER(key, uint32_t))) {
while (len >= sizeof(uint32_t)) {
uint32_t k = *(const uint32_t *)data;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
data += sizeof(uint32_t);
len -= sizeof(uint32_t);
}
} else {
while (len >= sizeof(uint32_t)) {
uint32_t k;
k = data[0];
k |= data[1] << 8;
k |= data[2] << 16;
k |= data[3] << 24;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
data += sizeof(uint32_t);
len -= sizeof(uint32_t);
}
}
/* Handle the last few bytes of the input array. */
switch (len) {
case 3:
h ^= data[2] << 16;
/* FALLTHROUGH */
case 2:
h ^= data[1] << 8;
/* FALLTHROUGH */
case 1:
h ^= data[0];
h *= m;
}
/*
* Do a few final mixes of the hash to ensure the last few
* bytes are well-incorporated.
*/
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
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