intl/hash-string.h

   1 /* Description of GNU message catalog format: string hashing function.
   2    Copyright (C) 1995, 1997-1998, 2000-2003 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify it
   5    under the terms of the GNU Library General Public License as published
   6    by 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 GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with this program; if not, write to the Free Software
  16    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  17    USA.  */
  18
  19 /* @@ end of prolog @@ */
  20
  21 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  22 #define HASHWORDBITS 32
  23
  24
  25 /* Defines the so called `hashpjw' function by P.J. Weinberger
  26    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  27    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  28 static inline unsigned long int
  29 hash_string (const char *str_param)
  30 {
  31   unsigned long int hval, g;
  32   const char *str = str_param;
  33
  34   /* Compute the hash value for the given string.  */
  35   hval = 0;
  36   while (*str != '\0')
  37     {
  38       hval <<= 4;
  39       hval += (unsigned char) *str++;
  40       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  41       if (g != 0)
  42         {
  43           hval ^= g >> (HASHWORDBITS - 8);
  44           hval ^= g;
  45         }
  46     }
  47   return hval;
  48 }