wnhash(3)

NAME

wn_strhash, wn_ptrhash, wn_inthash, wn_memhash,

wn_cumhasho, wn_cumhashu - hash functions for common keys

SYNOPSIS

#include <wn/wnhash.h>
int wn_strhash(char s[])
int wn_ptrhash(ptr p)
int wn_inthash(int i)
int wn_memhash(ptr mem, int len)
wn_cumhasho(int *accum, int hash)
wn_cumhashu(int *accum, int hash)

DESCRIPTION

A <hash function> returns a pseudo-random integer which

depends on a <key> argument. The hash functions provided here

are very fast and produce very random looking results.

wn_strhash hashes a string.

wn_ptrhash hashes a pointer.

wn_inthash hashes an int.

wn_memhash hashes a memory block of size len. One can use

it to hash structures.

The above functions can be assembled to produce hash func

tions for more complicated data structures, possibly using

wn_cumhasho and wn_cumhashu as glue.

wn_cumhasho is designed to produce a joint hash value from

several base hash values. The base hash values are passed in

hash; the result is accumulated in <accum>. The resulting hash

value DEPENDS very heavily on the ORDER of accumulation.

wn_cumhashu is designed to produce a joint hash value from

several base hash values. The base hash values are passed in

hash; the result is accumulated in <accum>. The resulting hash

value does NOT DEPEND on the ORDER of accumulation.

If you are hashing together objects of different types,

use for glue the C bit exclusive-or operator <^> instead of the

above functions.

EXAMPLES

The following function produces a hash value for a list of

strings. The result depends very heavily on the order of the

list.

int string_list_hash(list)
wn_sll list;
{
wn_sll el;
int hash;
char *string;

hash = 0;

for(el = list;el != NULL;el=el->next)
{
string = el->contents;

wn_cumhasho(&hash,wn_strhash(string));
}

return(hash);
}

The following function produces a hash value for a set of

strings. The result does not depend on the order in which the

hash calls happen to occur.

int string_set_hash(wn_sll list)
wn_sll list;
{
wn_sll el;
int hash;
char *string;

hash = 0;

for(el=list;el!=NULL;el=el->next)
{
string = el->contents;

wn_cumhashu(&hash,wn_strhash(string));
}

return(hash);
}

SEE ALSO

wn_mkhtab(3), wn_mkhashhtab(3)

AUTHOR

Will Naylor

WNLIB August 23, 1998

WNHASH(3)