text: // 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
  