src/intl/gettext/hash-string.h

   1 /* Description of GNU message catalog format: string hashing function.
   2    Copyright (C) 1995, 1997, 1998, 2000, 2001 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 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  19 #define HASHWORDBITS 32
  20
  21 /* Defines the so called `hashpjw' function by P.J. Weinberger
  22    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  23    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  24 static unsigned long int hash_string(const unsigned char *__str_param);
  25
  26 static inline unsigned long int
  27 hash_string(const unsigned char *str_param)
  28 {
  29         unsigned long int hval, g;
  30         const unsigned char *str = str_param;
  31
  32         /* Compute the hash value for the given string.  */
  33         hval = 0;
  34         while (*str != '\0') {
  35                 hval <<= 4;
  36                 hval += (unsigned long int) *str++;
  37                 g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  38                 if (g != 0) {
  39                         hval ^= g >> (HASHWORDBITS - 8);
  40                         hval ^= g;
  41                 }
  42         }
  43         return hval;
  44 }