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 
9 #include "murmurhash2.h"
10 
11 uint32_t
12 murmurhash2(const void * key, int len, uint32_t seed)
13 {
14   // 'm' and 'r' are mixing constants generated offline.
15   // They're not really 'magic', they just happen to work well.
16 
17   const uint32_t m = 0x5bd1e995;
18   const int r = 24;
19 
20   // Initialize the hash to a 'random' value
21 
22   uint32_t h = seed ^ len;
23 
24   // Mix 4 bytes at a time into the hash
25 
26   const unsigned char *data = (const unsigned char *)key;
27 
28   while(len >= 4)
29   {
30     uint32_t k = *(uint32_t*)data;
31 
32     k *= m;
33     k ^= k >> r;
34     k *= m;
35 
36     h *= m;
37     h ^= k;
38 
39     data += 4;
40     len -= 4;
41   }
42 
43   // Handle the last few bytes of the input array
44 
45   switch(len)
46   {
47   case 3: h ^= data[2] << 16;
48   case 2: h ^= data[1] << 8;
49   case 1: h ^= data[0];
50       h *= m;
51   };
52 
53   // Do a few final mixes of the hash to ensure the last few
54   // bytes are well-incorporated.
55 
56   h ^= h >> 13;
57   h *= m;
58   h ^= h >> 15;
59 
60   return h;
61 }