1 /* SPDX-License-Identifier: LicenseRef-murmurhash2-public-domain */
2 //-----------------------------------------------------------------------------
3 // MurmurHash2 was written by Austin Appleby, and is placed in the public
4 // domain. The author hereby disclaims copyright to this source code.
5
6 // Note - This code makes a few assumptions about how your machine behaves -
7
8 // 1. We can read a 4-byte value from any address without crashing
9 // 2. sizeof(int) == 4
10
11 // And it has a few limitations -
12
13 // 1. It will not work incrementally.
14 // 2. It will not produce the same results on little-endian and big-endian
15 // machines.
16
17 #include "MurmurHash2.h"
18
19 #if __GNUC__ >= 7
20 _Pragma("GCC diagnostic ignored \"-Wimplicit-fallthrough\"")
21 #endif
22
23 //-----------------------------------------------------------------------------
24 // Platform-specific functions and macros
25
26 // Microsoft Visual Studio
27
28 #if defined(_MSC_VER)
29
30 #define BIG_CONSTANT(x) (x)
31
32 // Other compilers
33
34 #else // defined(_MSC_VER)
35
36 #define BIG_CONSTANT(x) (x##LLU)
37
38 #endif // !defined(_MSC_VER)
39
40 //-----------------------------------------------------------------------------
41
MurmurHash2(const void * key,int len,uint32_t seed)42 uint32_t MurmurHash2 ( const void * key, int len, uint32_t seed )
43 {
44 // 'm' and 'r' are mixing constants generated offline.
45 // They're not really 'magic', they just happen to work well.
46
47 const uint32_t m = 0x5bd1e995;
48 const int r = 24;
49
50 // Initialize the hash to a 'random' value
51
52 uint32_t h = seed ^ len;
53
54 // Mix 4 bytes at a time into the hash
55
56 const unsigned char * data = (const unsigned char *)key;
57
58 while (len >= 4)
59 {
60 uint32_t k = *(uint32_t*)data;
61
62 k *= m;
63 k ^= k >> r;
64 k *= m;
65
66 h *= m;
67 h ^= k;
68
69 data += 4;
70 len -= 4;
71 }
72
73 // Handle the last few bytes of the input array
74
75 switch(len)
76 {
77 case 3: h ^= data[2] << 16; /* fall through */
78 case 2: h ^= data[1] << 8; /* fall through */
79 case 1: h ^= data[0]; /* fall through */
80 h *= m;
81 };
82
83 // Do a few final mixes of the hash to ensure the last few
84 // bytes are well-incorporated.
85
86 h ^= h >> 13;
87 h *= m;
88 h ^= h >> 15;
89
90 return h;
91 }
92