sgsnemu/lookup.c

/* 
 * Hash lookup function.
 * Copyright (C) 2003, 2004 Mondru AB.
 * 
 * The contents of this file may be used under the terms of the GNU
 * General Public License Version 2, provided that the above copyright
 * notice and this permission notice is included in all copies or
 * substantial portions of the software.
 * 
 */

/**
 * lookup()
 * Generates a 32 bit hash.
 * Based on public domain code by Bob Jenkins
 * It should be one of the best hash functions around in terms of both
 * statistical properties and speed. It is NOT recommended for cryptographic
 * purposes.
 **/
unsigned long int lookup( k, length, level)
register unsigned char *k;         /* the key */
register unsigned long int length; /* the length of the key */
register unsigned long int level; /* the previous hash, or an arbitrary value*/
{

#define mix(a,b,c) \
{ \
  a -= b; a -= c; a ^= (c>>13); \
  b -= c; b -= a; b ^= (a<<8); \
  c -= a; c -= b; c ^= (b>>13); \
  a -= b; a -= c; a ^= (c>>12);  \
  b -= c; b -= a; b ^= (a<<16); \
  c -= a; c -= b; c ^= (b>>5); \
  a -= b; a -= c; a ^= (c>>3);  \
  b -= c; b -= a; b ^= (a<<10); \
  c -= a; c -= b; c ^= (b>>15); \
}

  typedef  unsigned long  int  ub4;   /* unsigned 4-byte quantities */
  typedef  unsigned       char ub1;   /* unsigned 1-byte quantities */
  register unsigned long int a,b,c,len;
  
  /* Set up the internal state */
  len = length;
  a = b = 0x9e3779b9;  /* the golden ratio; an arbitrary value */
  c = level;           /* the previous hash value */
  
  /*---------------------------------------- handle most of the key */
  while (len >= 12)
    {
      a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
      b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
      c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
      mix(a,b,c);
      k += 12; len -= 12;
    }
  
  /*------------------------------------- handle the last 11 bytes */
  c += length;
  switch(len)              /* all the case statements fall through */
    {
    case 11: c+=((ub4)k[10]<<24);
    case 10: c+=((ub4)k[9]<<16);
    case 9 : c+=((ub4)k[8]<<8);
      /* the first byte of c is reserved for the length */
    case 8 : b+=((ub4)k[7]<<24);
    case 7 : b+=((ub4)k[6]<<16);
    case 6 : b+=((ub4)k[5]<<8);
    case 5 : b+=k[4];
    case 4 : a+=((ub4)k[3]<<24);
    case 3 : a+=((ub4)k[2]<<16);
    case 2 : a+=((ub4)k[1]<<8);
    case 1 : a+=k[0];
      /* case 0: nothing left to add */
    }
  mix(a,b,c);
  /*-------------------------------------------- report the result */
  return c;
}