单向HASH——MurmurHash

//seed 是大质数
unsigned long long MurmurHash64B ( const void * key, int 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;
 
    unsigned long long h = h1;
 
    h = (h << 32) | h2;
 
    return h;
}