1 /* $NetBSD: murmurhash.c,v 1.8 2019/08/20 15:17:02 para 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 1.8 2019/08/20 15:17:02 para Exp $");
18
19 #include <lib/libkern/libkern.h>
20
21 #else
22
23 #if defined(LIBC_SCCS) && !defined(lint)
24 __RCSID("$NetBSD: murmurhash.c,v 1.8 2019/08/20 15:17:02 para Exp $");
25 #endif /* LIBC_SCCS and not lint */
26
27 #include "namespace.h"
28 #include <string.h>
29
30 #endif
31
32 #include <sys/types.h>
33 #include <sys/param.h>
34 #include <sys/hash.h>
35
36 #if !defined(_KERNEL) && !defined(_STANDALONE)
37 #ifdef __weak_alias
__weak_alias(murmurhash2,_murmurhash2)38 __weak_alias(murmurhash2,_murmurhash2)
39 #endif
40 #endif
41
42 uint32_t
43 murmurhash2(const void *key, size_t len, uint32_t seed)
44 {
45 /*
46 * Note: 'm' and 'r' are mixing constants generated offline.
47 * They're not really 'magic', they just happen to work well.
48 * Initialize the hash to a 'random' value.
49 */
50 const uint32_t m = 0x5bd1e995;
51 const int r = 24;
52
53 const uint8_t *data = key;
54 uint32_t h = seed ^ (uint32_t)len;
55
56 if (__predict_true(ALIGNED_POINTER(key, uint32_t))) {
57 while (len >= sizeof(uint32_t)) {
58 uint32_t k;
59
60 ALIGNED_POINTER_LOAD(&k, data, uint32_t);
61 k = htole32(k);
62
63 k *= m;
64 k ^= k >> r;
65 k *= m;
66
67 h *= m;
68 h ^= k;
69
70 data += sizeof(uint32_t);
71 len -= sizeof(uint32_t);
72 }
73 } else {
74 while (len >= sizeof(uint32_t)) {
75 uint32_t k;
76
77 k = data[0];
78 k |= data[1] << 8;
79 k |= data[2] << 16;
80 k |= data[3] << 24;
81
82 k *= m;
83 k ^= k >> r;
84 k *= m;
85
86 h *= m;
87 h ^= k;
88
89 data += sizeof(uint32_t);
90 len -= sizeof(uint32_t);
91 }
92 }
93
94 /* Handle the last few bytes of the input array. */
95 switch (len) {
96 case 3:
97 h ^= data[2] << 16;
98 /* FALLTHROUGH */
99 case 2:
100 h ^= data[1] << 8;
101 /* FALLTHROUGH */
102 case 1:
103 h ^= data[0];
104 h *= m;
105 }
106
107 /*
108 * Do a few final mixes of the hash to ensure the last few
109 * bytes are well-incorporated.
110 */
111 h ^= h >> 13;
112 h *= m;
113 h ^= h >> 15;
114
115 return h;
116 }
117