Collection of some frequently used hash functions

hash_func.c

// RS Hash Function
unsigned int
RSHash (char *str)
{
    unsigned int b = 378551;
    unsigned int a = 63689;
    unsigned int hash = 0;
    while (*str)
      {
	  hash = hash * a + (*str++);
	  a *= b;
      }
    return (hash & 0x7FFFFFFF);
}
 
// JS Hash Function
unsigned int
JSHash (char *str)
{
    unsigned int hash = 1315423911;
    while (*str)
      {
	  hash ^= ((hash << 5) + (*str++) + (hash >> 2));
      }
    return (hash & 0x7FFFFFFF);
}
 
// P. J. Weinberger Hash Function
unsigned int
PJWHash (char *str)
{
    unsigned int BitsInUnignedInt = (unsigned int) (sizeof (unsigned
							    int) * 8);
    unsigned int ThreeQuarters = (unsigned int) ((BitsInUnignedInt * 3) / 4);
    unsigned int OneEighth = (unsigned int) (BitsInUnignedInt / 8);
    unsigned int HighBits = (unsigned int) (0xFFFFFFFF) <<
	(BitsInUnignedInt - OneEighth);
    unsigned int hash = 0;
    unsigned int test = 0;
    while (*str)
      {
	  hash = (hash << OneEighth) + (*str++);
	  if ((test = hash & HighBits) != 0)
	    {
		hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
	    }
      }
    return (hash & 0x7FFFFFFF);
}
 
// ELF Hash Function
unsigned int
ELFHash (char *str)
{
    unsigned int hash = 0;
    unsigned int x = 0;
    while (*str)
      {
	  hash = (hash << 4) + (*str++);
	  if ((x = hash & 0xF0000000L) != 0)
	    {
		hash ^= (x >> 24);
		hash &= ~x;
	    }
      }
    return (hash & 0x7FFFFFFF);
}
 
// BKDR Hash Function
unsigned int
BKDRHash (char *str)
{
    unsigned int seed = 131;	// 31 131 1313 13131 131313 etc..
    unsigned int hash = 0;
    while (*str)
      {
	  hash = hash * seed + (*str++);
      }
    return (hash & 0x7FFFFFFF);
}
 
// SDBM Hash Function
unsigned int
SDBMHash (char *str)
{
    unsigned int hash = 0;
    while (*str)
      {
	  hash = (*str++) + (hash << 6) + (hash << 16) - hash;
      }
    return (hash & 0x7FFFFFFF);
}
 
// DJB Hash Function
unsigned int
DJBHash (char *str)
{
    unsigned int hash = 5381;
    while (*str)
      {
	  hash += (hash << 5) + (*str++);
      }
    return (hash & 0x7FFFFFFF);
}
 
// AP Hash Function
unsigned int
APHash (char *str)
{
    unsigned int hash = 0;
    int i;
    for (i = 0; *str; i++)
      {
	  if ((i & 1) == 0)
	    {
		hash ^= ((hash << 7) ^ (*str++) ^ (hash >> 3));
	    }
	  else
	    {
		hash ^= (~((hash << 11) ^ (*str++) ^ (hash >> 5)));
	    }
      }
    return (hash & 0x7FFFFFFF);
}