mosesdecoder/kenlm/util/murmur_hash.cc

/* Downloaded from http://sites.google.com/site/murmurhash/ which says "All
 * code is released to the public domain. For business purposes, Murmurhash is
 * under the MIT license."
 * This is modified from the original:
 * ULL tag on 0xc6a4a7935bd1e995 so this will compile on 32-bit.  
 * length changed to unsigned int.  
 * placed in namespace util
 * add MurmurHashNative
 * default option = 0 for seed
 */

#include "util/murmur_hash.hh"

namespace util {

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

// The same caveats as 32-bit MurmurHash2 apply here - beware of alignment 
// and endian-ness issues if used across multiple platforms.

// 64-bit hash for 64-bit platforms

uint64_t MurmurHash64A ( const void * key, std::size_t len, unsigned int seed )
{
  const uint64_t m = 0xc6a4a7935bd1e995ULL;
  const int r = 47;

  uint64_t h = seed ^ (len * m);

  const uint64_t * data = (const uint64_t *)key;
  const uint64_t * end = data + (len/8);

  while(data != end)
  {
    uint64_t k = *data++;

    k *= m; 
    k ^= k >> r; 
    k *= m; 
    
    h ^= k;
    h *= m; 
  }

  const unsigned char * data2 = (const unsigned char*)data;

  switch(len & 7)
  {
  case 7: h ^= uint64_t(data2[6]) << 48;
  case 6: h ^= uint64_t(data2[5]) << 40;
  case 5: h ^= uint64_t(data2[4]) << 32;
  case 4: h ^= uint64_t(data2[3]) << 24;
  case 3: h ^= uint64_t(data2[2]) << 16;
  case 2: h ^= uint64_t(data2[1]) << 8;
  case 1: h ^= uint64_t(data2[0]);
          h *= m;
  };
 
  h ^= h >> r;
  h *= m;
  h ^= h >> r;

  return h;
} 


// 64-bit hash for 32-bit platforms

uint64_t MurmurHash64B ( const void * key, std::size_t len, unsigned int seed )
{
  const unsigned int m = 0x5bd1e995;
  const int r = 24;

  unsigned int h1 = seed ^ len;
  unsigned int h2 = 0;

  const unsigned int * data = (const unsigned int *)key;

  while(len >= 8)
  {
    unsigned int k1 = *data++;
    k1 *= m; k1 ^= k1 >> r; k1 *= m;
    h1 *= m; h1 ^= k1;
    len -= 4;

    unsigned int k2 = *data++;
    k2 *= m; k2 ^= k2 >> r; k2 *= m;
    h2 *= m; h2 ^= k2;
    len -= 4;
  }

  if(len >= 4)
  {
    unsigned int k1 = *data++;
    k1 *= m; k1 ^= k1 >> r; k1 *= m;
    h1 *= m; h1 ^= k1;
    len -= 4;
  }

  switch(len)
  {
  case 3: h2 ^= ((unsigned char*)data)[2] << 16;
  case 2: h2 ^= ((unsigned char*)data)[1] << 8;
  case 1: h2 ^= ((unsigned char*)data)[0];
      h2 *= m;
  };

  h1 ^= h2 >> 18; h1 *= m;
  h2 ^= h1 >> 22; h2 *= m;
  h1 ^= h2 >> 17; h1 *= m;
  h2 ^= h1 >> 19; h2 *= m;

  uint64_t h = h1;

  h = (h << 32) | h2;

  return h;
}

uint64_t MurmurHashNative(const void * key, std::size_t len, unsigned int seed) {
  if (sizeof(int) == 4) {
    return MurmurHash64B(key, len, seed);
  } else {
    return MurmurHash64A(key, len, seed);
  }
}

} // namespace util