1 /**
2 * Compiler implementation of the D programming language
3 * http://dlang.org
4 *
5 * Copyright: Copyright (C) 1999-2021 by The D Language Foundation, All Rights Reserved
6 * Authors: Martin Nowak, Walter Bright, http://www.digitalmars.com
7 * License: $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
8 * Source: $(DMDSRC root/_hash.h)
9 */
10
11 #pragma once
12
13 #include "dsystem.h" // uint{8|16|32}_t
14
15 // MurmurHash2 was written by Austin Appleby, and is placed in the public
16 // domain. The author hereby disclaims copyright to this source code.
17 // https://sites.google.com/site/murmurhash/
calcHash(const uint8_t * data,size_t len)18 static inline uint32_t calcHash(const uint8_t *data, size_t len)
19 {
20 // 'm' and 'r' are mixing constants generated offline.
21 // They're not really 'magic', they just happen to work well.
22
23 const uint32_t m = 0x5bd1e995;
24 const int r = 24;
25
26 // Initialize the hash to a 'random' value
27
28 uint32_t h = (uint32_t)len;
29
30 // Mix 4 bytes at a time into the hash
31
32 while(len >= 4)
33 {
34 uint32_t k = data[3] << 24 | data[2] << 16 | data[1] << 8 | data[0];
35
36 k *= m;
37 k ^= k >> r;
38 k *= m;
39
40 h *= m;
41 h ^= k;
42
43 data += 4;
44 len -= 4;
45 }
46
47 // Handle the last few bytes of the input array
48
49 switch(len & 3)
50 {
51 case 3: h ^= data[2] << 16; /* fall through */
52 case 2: h ^= data[1] << 8; /* fall through */
53 case 1: h ^= data[0];
54 h *= m;
55 }
56
57 // Do a few final mixes of the hash to ensure the last few
58 // bytes are well-incorporated.
59
60 h ^= h >> 13;
61 h *= m;
62 h ^= h >> 15;
63
64 return h;
65 }
66
calcHash(const char * data,size_t len)67 static inline uint32_t calcHash(const char *data, size_t len)
68 {
69 return calcHash((const uint8_t *)data, len);
70 }
71
72 // combine and mix two words (boost::hash_combine)
mixHash(size_t h,size_t k)73 static inline size_t mixHash(size_t h, size_t k)
74 {
75 return h ^ (k + 0x9e3779b9 + (h << 6) + (h >> 2));
76 }
77