xref: /freebsd/sys/libkern/murmur3_32.c (revision 1068aa420151ff338c189bfe6f3ed858b937495d)
1 /*-
2  * Copyright (c) 2014 Dag-Erling Smørgrav
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  */
26 
27 #include <sys/hash.h>
28 #include <sys/endian.h>
29 #include <sys/stdint.h>
30 #include <sys/types.h>
31 
32 #define rol32(i32, n) ((i32) << (n) | (i32) >> (32 - (n)))
33 
34 /*
35  * $FreeBSD$
36  * Simple implementation of the Murmur3-32 hash function optimized for
37  * aligned sequences of 32-bit words.  If len is not a multiple of 4, it
38  * will be rounded down, droping trailer bytes.
39  */
40 uint32_t
41 murmur3_aligned_32(const void *data, size_t len, uint32_t seed)
42 {
43 	const uint32_t *data32;
44 	uint32_t hash, k;
45 	size_t res;
46 
47 	/* initialize */
48 	len -= len % sizeof(*data32);
49 	res = len;
50 	data32 = data;
51 	hash = seed;
52 
53 	/* iterate */
54 	for (res = 0; res < len; res += sizeof(*data32), data32++) {
55 		k = le32toh(*data32);
56 		k *= 0xcc9e2d51;
57 		k = rol32(k, 15);
58 		k *= 0x1b873593;
59 		hash ^= k;
60 		hash = rol32(hash, 13);
61 		hash *= 5;
62 		hash += 0xe6546b64;
63 	}
64 
65 	/* finalize */
66 	hash ^= (uint32_t)len;
67 	hash ^= hash >> 16;
68 	hash *= 0x85ebca6b;
69 	hash ^= hash >> 13;
70 	hash *= 0xc2b2ae35;
71 	hash ^= hash >> 16;
72 	return (hash);
73 }
74 
75