1 /*	$NetBSD: murmurhash.c,v 1.6 2013/10/26 21:06:38 rmind Exp $	*/
2 
3 /*
4  * MurmurHash2 -- from the original code:
5  *
6  * "MurmurHash2 was written by Austin Appleby, and is placed in the public
7  * domain. The author hereby disclaims copyright to this source code."
8  *
9  * References:
10  *	http://code.google.com/p/smhasher/
11  *	https://sites.google.com/site/murmurhash/
12  */
13 
14 #include <sys/cdefs.h>
15 
16 #if defined(_KERNEL) || defined(_STANDALONE)
17 __KERNEL_RCSID(0, "$NetBSD: murmurhash.c,v 1.6 2013/10/26 21:06:38 rmind Exp $");
18 
19 #else
20 
21 #if defined(LIBC_SCCS) && !defined(lint)
22 __RCSID("$NetBSD: murmurhash.c,v 1.6 2013/10/26 21:06:38 rmind Exp $");
23 #endif /* LIBC_SCCS and not lint */
24 
25 #include "namespace.h"
26 #endif
27 
28 #include <sys/types.h>
29 #include <sys/param.h>
30 #include <sys/hash.h>
31 
32 #if !defined(_KERNEL) && !defined(_STANDALONE)
33 #ifdef __weak_alias
34 __weak_alias(murmurhash2,_murmurhash2)
35 #endif
36 #endif
37 
38 uint32_t
39 murmurhash2(const void *key, size_t len, uint32_t seed)
40 {
41 	/*
42 	 * Note: 'm' and 'r' are mixing constants generated offline.
43 	 * They're not really 'magic', they just happen to work well.
44 	 * Initialize the hash to a 'random' value.
45 	 */
46 	const uint32_t m = 0x5bd1e995;
47 	const int r = 24;
48 
49 	const uint8_t *data = key;
50 	uint32_t h = seed ^ (uint32_t)len;
51 
52 	if (__predict_true(ALIGNED_POINTER(key, uint32_t))) {
53 		while (len >= sizeof(uint32_t)) {
54 			uint32_t k = *(const uint32_t *)data;
55 
56 			k *= m;
57 			k ^= k >> r;
58 			k *= m;
59 
60 			h *= m;
61 			h ^= k;
62 
63 			data += sizeof(uint32_t);
64 			len -= sizeof(uint32_t);
65 		}
66 	} else {
67 		while (len >= sizeof(uint32_t)) {
68 			uint32_t k;
69 
70 			k  = data[0];
71 			k |= data[1] << 8;
72 			k |= data[2] << 16;
73 			k |= data[3] << 24;
74 
75 			k *= m;
76 			k ^= k >> r;
77 			k *= m;
78 
79 			h *= m;
80 			h ^= k;
81 
82 			data += sizeof(uint32_t);
83 			len -= sizeof(uint32_t);
84 		}
85 	}
86 
87 	/* Handle the last few bytes of the input array. */
88 	switch (len) {
89 	case 3:
90 		h ^= data[2] << 16;
91 		/* FALLTHROUGH */
92 	case 2:
93 		h ^= data[1] << 8;
94 		/* FALLTHROUGH */
95 	case 1:
96 		h ^= data[0];
97 		h *= m;
98 	}
99 
100 	/*
101 	 * Do a few final mixes of the hash to ensure the last few
102 	 * bytes are well-incorporated.
103 	 */
104 	h ^= h >> 13;
105 	h *= m;
106 	h ^= h >> 15;
107 
108 	return h;
109 }
110