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So i'm writing a hashing program for one of my classes and he's letting us find a hashing function online. However when I use the following hashing function I get huge numbers. My question is, do I have to mod the answer I get from this function with the size of my table or am I doing something wrong? 

  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;
}
Iriketurtles
  • 33
  • 5
  • Yeah, hashes tend to look like uniformly random data distributed over all bits in the hash output value. So a 32-bit hash will likely have a value close to 2 to the power of 32 when placed in an unsigned 32 bit int. So you are right, you should use a mod operatoion % or & (for speed, restricted to powers of 2) to match your table size. – Christopher Oicles Mar 23 '16 at 21:33
  • @ChristopherOicles thank you, just wanted to make sure because it wasn't included in the code. – Iriketurtles Mar 24 '16 at 01:08

0 Answers0