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
38__weak_alias(murmurhash2,_murmurhash2)
39#endif
40#endif
41
42uint32_t
43murmurhash2(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