intl/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 /* @@ end of prolog @@ */
  19
  20 #ifndef PARAMS
  21 # if __STDC__
  22 #  define PARAMS(Args) Args
  23 # else
  24 #  define PARAMS(Args) ()
  25 # endif
  26 #endif
  27
  28 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  29 #define HASHWORDBITS 32
  30
  31
  32 /* Defines the so called `hashpjw' function by P.J. Weinberger
  33    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  34    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  35 static unsigned long int hash_string PARAMS ((const char *__str_param));
  36
  37 static inline unsigned long int
  38 hash_string (str_param)
  39      const char *str_param;
  40 {
  41   unsigned long int hval, g;
  42   const char *str = str_param;
  43
  44   /* Compute the hash value for the given string.  */
  45   hval = 0;
  46   while (*str != '\0')
  47     {
  48       hval <<= 4;
  49       hval += (unsigned long int) *str++;
  50       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  51       if (g != 0)
  52         {
  53           hval ^= g >> (HASHWORDBITS - 8);
  54           hval ^= g;
  55         }
  56     }
  57   return hval;
  58 }