91 lines
1.8 KiB
C
91 lines
1.8 KiB
C
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/* $NetBSD: murmurhash.c,v 1.4 2012/07/10 17:05:38 christos Exp $ */
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/*
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* MurmurHash2 -- from the original code:
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*
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* "MurmurHash2 was written by Austin Appleby, and is placed in the public
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* domain. The author hereby disclaims copyright to this source code."
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*
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* References:
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* http://code.google.com/p/smhasher/
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* https://sites.google.com/site/murmurhash/
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*/
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#include <sys/cdefs.h>
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#if defined(_KERNEL) || defined(_STANDALONE)
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__KERNEL_RCSID(0, "$NetBSD: murmurhash.c,v 1.4 2012/07/10 17:05:38 christos Exp $");
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#else
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#if defined(LIBC_SCCS) && !defined(lint)
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__RCSID("$NetBSD: murmurhash.c,v 1.4 2012/07/10 17:05:38 christos Exp $");
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#endif /* LIBC_SCCS and not lint */
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#include "namespace.h"
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#endif
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#include <sys/types.h>
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#include <sys/hash.h>
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#ifdef __weak_alias
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__weak_alias(murmurhash2,_murmurhash2)
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#endif
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uint32_t
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murmurhash2(const void *key, size_t len, uint32_t seed)
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{
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/*
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* Note: 'm' and 'r' are mixing constants generated offline.
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* They're not really 'magic', they just happen to work well.
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* Initialize the hash to a 'random' value.
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*/
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const uint32_t m = 0x5bd1e995;
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const int r = 24;
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const uint8_t *data = key;
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uint32_t h = seed ^ (uint32_t)len;
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while (len >= sizeof(uint32_t)) {
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uint32_t k;
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k = data[0];
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k |= data[1] << 8;
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k |= data[2] << 16;
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k |= data[3] << 24;
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k *= m;
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k ^= k >> r;
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k *= m;
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h *= m;
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h ^= k;
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data += sizeof(uint32_t);
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len -= sizeof(uint32_t);
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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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/* FALLTHROUGH */
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case 2:
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h ^= data[1] << 8;
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/* FALLTHROUGH */
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case 1:
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h ^= data[0];
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h *= m;
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}
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/*
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* Do a few final mixes of the hash to ensure the last few
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* bytes are well-incorporated.
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*/
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h ^= h >> 13;
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h *= m;
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h ^= h >> 15;
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return h;
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}
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