SuperFastHash.cpp

#include "Platform.h"
#include <stdio.h> // for NULL

/* By Paul Hsieh (C) 2004, 2005.  Covered under the Paul Hsieh derivative 
   license. See: 
   http://www.azillionmonkeys.com/qed/weblicense.html for license details.

   http://www.azillionmonkeys.com/qed/hash.html */

#undef get16bits
#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
  || defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
#define get16bits(d) (*((const uint16_t *) (d)))
#endif

#if !defined (get16bits)
#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
                       +(uint32_t)(((const uint8_t *)(d))[0]) )
#endif

uint32_t SuperFastHash (const char * data, int len) {
uint32_t hash = 0, 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_t);
    hash  += hash >> 11;
  }

  /* Handle end cases */
  switch (rem) {
    case 3:	hash += get16bits (data);
        hash ^= hash << 16;
        hash ^= data[sizeof (uint16_t)] << 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;
}

void SuperFastHash     ( const void * key, int len, uint32_t /*seed*/, void * out )
{
  *(uint32_t*)out = SuperFastHash((const char*)key,len);
}