gnu/dist/texinfo/intl/hash-string.h

   1 /*      $NetBSD$        */
   2
   3 /* Description of GNU message catalog format: string hashing function.
   4    Copyright (C) 1995, 1997-1998, 2000-2003 Free Software Foundation, Inc.
   5
   6    This program is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU Library General Public License as published
   8    by the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with this program; if not, write to the Free Software
  18    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  19    USA.  */
  20
  21 /* @@ end of prolog @@ */
  22
  23 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  24 #define HASHWORDBITS 32
  25
  26
  27 /* Defines the so called `hashpjw' function by P.J. Weinberger
  28    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  29    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  30 static inline unsigned long int
  31 hash_string (const char *str_param)
  32 {
  33   unsigned long int hval, g;
  34   const char *str = str_param;
  35
  36   /* Compute the hash value for the given string.  */
  37   hval = 0;
  38   while (*str != '\0')
  39     {
  40       hval <<= 4;
  41       hval += (unsigned char) *str++;
  42       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  43       if (g != 0)
  44         {
  45           hval ^= g >> (HASHWORDBITS - 8);
  46           hval ^= g;
  47         }
  48     }
  49   return hval;
  50 }