super hash function by Paul Hsieh

gistfile1.txt

// Fast Hash

#if !defined (get16bits)
#define get16bits(d) ((((uint32)(((const uint8 *)(d))[1])) << 8)\
+(uint32)(((const uint8 *)(d))[0]) )
#endif
//
// super hash function by Paul Hsieh
//
inline uint32 superFastHash (const char * data, int len) {
  uint32 hash = len, tmp;
	int rem;

    if (len <= 0 || data == NULL) return 0;

    rem = len & 3;
    len >>= 2;

    /* Main loop */
    for (;len > 0; len--) {
        hash  += get16bits (data);
        tmp    = (get16bits (data+2) << 11) ^ hash;
        hash   = (hash << 16) ^ tmp;
        data  += 2*sizeof (uint16);
        hash  += hash >> 11;
    }

    /* Handle end cases */
    switch (rem) {
        case 3: hash += get16bits (data);
			hash ^= hash << 16;
			hash ^= data[sizeof (uint16)] << 18;
			hash += hash >> 11;
			break;
        case 2: hash += get16bits (data);
			hash ^= hash << 11;
			hash += hash >> 17;
			break;
        case 1: hash += *data;
			hash ^= hash << 10;
			hash += hash >> 1;
    }

    /* Force "avalanching" of final 127 bits */
    hash ^= hash << 3;
    hash += hash >> 5;
    hash ^= hash << 4;
    hash += hash >> 17;
    hash ^= hash << 25;
    hash += hash >> 6;

    return hash;
}