root/hash.c

/* */

---

DEFINITIONS

This source file includes following definitions.

1. mmh2a

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   1 //-----------------------------------------------------------------------------

   2 // MurmurHash2, 64-bit versions, by Austin Appleby

   3 
   4 // The same caveats as 32-bit MurmurHash2 apply here - beware of alignment 

   5 // and endian-ness issues if used across multiple platforms.

   6 
   7 #include "hash.h"
   8 
   9 uint64_t mmh2a(const void *key, int len, unsigned int seed) {
  10         const uint64_t m = 0xc6a4a7935bd1e995;
  11         const int r = 47;
  12 
  13         uint64_t h = seed ^ (len * m);
  14 
  15         const uint64_t *data = (const uint64_t *)key;
  16         const uint64_t *end = data + (len/8);
  17 
  18         while(data != end) {
  19                 uint64_t k = *data++;
  20 
  21                 k *= m; 
  22                 k ^= k >> r; 
  23                 k *= m; 
  24                 
  25                 h ^= k;
  26                 h *= m; 
  27         }
  28 
  29         const unsigned char *data2 = (const unsigned char*)data;
  30 
  31         switch(len & 7) {
  32         case 7: h ^= (uint64_t)data2[6] << 48;
  33         case 6: h ^= (uint64_t)data2[5] << 40;
  34         case 5: h ^= (uint64_t)data2[4] << 32;
  35         case 4: h ^= (uint64_t)data2[3] << 24;
  36         case 3: h ^= (uint64_t)data2[2] << 16;
  37         case 2: h ^= (uint64_t)data2[1] << 8;
  38         case 1: h ^= (uint64_t)data2[0];
  39                 h *= m;
  40         };
  41  
  42         h ^= h >> r;
  43         h *= m;
  44         h ^= h >> r;
  45 
  46         return h;

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/* */