lib/hash-pjw.c

   1 /* hash-pjw.c -- compute a hash value from a NUL-terminated string.
   2    Copyright (C) 2001, 2003 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 #if HAVE_CONFIG_H
  19 # include <config.h>
  20 #endif
  21
  22 #include "hash-pjw.h"
  23
  24 #include <limits.h>
  25
  26 #define SIZE_BITS (sizeof (size_t) * CHAR_BIT)
  27
  28 /* A hash function for NUL-terminated char* strings using
  29    the method described by Bruno Haible.
  30    See http://www.haible.de/bruno/hashfunc.html.  */
  31
  32 size_t
  33 hash_pjw (const void *x, size_t tablesize)
  34 {
  35   const char *s;
  36   size_t h = 0;
  37
  38   for (s = x; *s; s++)
  39     h = *s + ((h << 9) | (h >> (SIZE_BITS - 9)));
  40
  41   return h % tablesize;
  42 }