thodg/got/lib/murmurhash2.c

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• Hash : 5df018ff
  Author :
  Date : 2021-10-14T16:03:22
  

  rework murmurhash2() to avoid potential unaligned memory access pointed out by naddy@ ok millert@

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• lib/murmurhash2.c

• //-----------------------------------------------------------------------------
  // MurmurHash2 was written by Austin Appleby, and is placed in the public
  // domain. The author hereby disclaims copyright to this source code.
  
  /* Obtained from https://github.com/aappleby/smhasher */
  
  #include <stdint.h>
  #include <string.h>
  
  #include "murmurhash2.h"
  
  uint32_t
  murmurhash2(const unsigned char * key, int len, uint32_t seed)
  {
    // 'm' and 'r' are mixing constants generated offline.
    // They're not really 'magic', they just happen to work well.
  
    const uint32_t m = 0x5bd1e995;
    const int r = 24;
  
    // Initialize the hash to a 'random' value
  
    uint32_t h = seed ^ len;
  
    // Mix 4 bytes at a time into the hash
  
    const unsigned char *data = key;
  
    while(len >= 4)
    {
      uint32_t k;
  
      memcpy(&k, data, sizeof(k));
  
      k *= m;
      k ^= k >> r;
      k *= m;
  
      h *= m;
      h ^= k;
  
      data += 4;
      len -= 4;
    }
  
    // Handle the last few bytes of the input array
  
    switch(len)
    {
    case 3: h ^= data[2] << 16;
    case 2: h ^= data[1] << 8;
    case 1: h ^= data[0];
        h *= m;
    };
  
    // Do a few final mixes of the hash to ensure the last few
    // bytes are well-incorporated.
  
    h ^= h >> 13;
    h *= m;
    h ^= h >> 15;
  
    return h;
  }
  

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