// File: crn_hash.cpp
// See Paul Hsieh's page at: http://www.azillionmonkeys.com/qed/hash.html
// Also see http://www.concentric.net/~Ttwang/tech/inthash.htm,
// http://burtleburtle.net/bob/hash/integer.html
#include "crn_core.h"

#undef get16bits
#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
   || defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
#define get16bits(d) (*((const uint16 *) (d)))
#endif

#if !defined (get16bits)
#define get16bits(d) ((((uint32)(((const uint8 *)(d))[1])) << 8)\
   +(uint32)(((const uint8 *)(d))[0]) )
#endif

namespace crnlib
{
   uint32 fast_hash (const void* p, int len) 
   {
      const char * data = static_cast<const char *>(p);
      
      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;
   }

}  // namespace crnlib