murmurhash2和djb

两个hash算法

1、djb算法

    /* the famous DJB Hash Function for strings */  
    unsigned int DJBHash(char *str)  
    {  
        unsigned int hash = 5381;  
       
        while (*str){  
            hash = ((hash << 5) + hash) + (*str++); /* times 33 */  
        }  
        hash &= ~(1 << 31); /* strip the highest bit */  
        return hash;  
    }  

以上代码取自http://blog.csdn.net/chaosinux/article/details/7853394
2、murmurhash2算法

uint32_t
ngx_murmur_hash2(u_char *data, size_t len)
{
    uint32_t  h, k;

    h = 0 ^ len;

    while (len >= 4) {
        k  = data[0];
        k |= data[1] << 8;
        k |= data[2] << 16;
        k |= data[3] << 24;

        k *= 0x5bd1e995;
        k ^= k >> 24;
        k *= 0x5bd1e995;

        h *= 0x5bd1e995;
        h ^= k;

        data += 4;
        len -= 4;
    }

    switch (len) {
    case 3:
        h ^= data[2] << 16;
    case 2:
        h ^= data[1] << 8;
    case 1:
        h ^= data[0];
        h *= 0x5bd1e995;
    }

    h ^= h >> 13;
    h *= 0x5bd1e995;
    h ^= h >> 15;

    return h;
}

以上代码取自是nginx
murmurhash算法评测

速度评测

    OneAtATime -354.163715 mb/sec
    FNV -443.668038 mb/sec
   SuperFastHash - 985.335173 mb/sec
    lookup3 -988.080652 mb/sec
    MurmurHash1.0 - 1363.293480 mb/sec
    MurmurHash2.0 - 2056.885653 mb/sec

3、原始版本的murmurhash2算法（Google Code 的 Murmurhash 开源项目主页上的 Murmurhash2）

uint32_t MurmurHash2 ( const void * 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 = (const unsigned char *)key;

  while(len >= 4)
  {
    uint32_t k = *(uint32_t*)data;

    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;
}

这个地址：http://blog.csdn.net/wwwsq/article/details/4254123有对这两个算法的比较