1 //-----------------------------------------------------------------------------
2 // MurmurHash2 was written by Austin Appleby, and is placed in the public
3 // domain. The author hereby disclaims copyright to this source code.
4 
5 /* Obtained from https://github.com/aappleby/smhasher */
6 
7 #include <stdint.h>
8 #include <string.h>
9 
10 #include "murmurhash2.h"
11 
12 uint32_t
13 murmurhash2(const unsigned char * key, int len, uint32_t seed)
14 {
15   // 'm' and 'r' are mixing constants generated offline.
16   // They're not really 'magic', they just happen to work well.
17 
18   const uint32_t m = 0x5bd1e995;
19   const int r = 24;
20 
21   // Initialize the hash to a 'random' value
22 
23   uint32_t h = seed ^ len;
24 
25   // Mix 4 bytes at a time into the hash
26 
27   const unsigned char *data = key;
28 
29   while(len >= 4)
30   {
31     uint32_t k;
32 
33     memcpy(&k, data, sizeof(k));
34 
35     k *= m;
36     k ^= k >> r;
37     k *= m;
38 
39     h *= m;
40     h ^= k;
41 
42     data += 4;
43     len -= 4;
44   }
45 
46   // Handle the last few bytes of the input array
47 
48   switch(len)
49   {
50   case 3: h ^= data[2] << 16;
51   case 2: h ^= data[1] << 8;
52   case 1: h ^= data[0];
53       h *= m;
54   };
55 
56   // Do a few final mixes of the hash to ensure the last few
57   // bytes are well-incorporated.
58 
59   h ^= h >> 13;
60   h *= m;
61   h ^= h >> 15;
62 
63   return h;
64 }