man wnhash (Fonctions bibliothèques) - hash functions for common keys

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 functions 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

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