NAME
     wnhash -- hash functions for common keys

SYNOPSIS
     #include "wnhash.h"

     int wn_strhash(s)
     char s[];

     int wn_ptrhash(p)
     ptr p;

     int wn_inthash(i)
     int i;

     int wn_memhash(mem,len)
     ptr mem;
     int len;

     wn_cumhasho(&accum,hash)
     int accum,hash;

     wn_cumhashu(&accum,hash)
     int accum,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);
       }
  
DIAGNOSTICS
  
BUGS

SEE ALSO
     wnhtab, wnhtbl

AUTHOR
     Will Naylor