intl/hash-string.h

   1 /* hash-string - Implements a string hashing function.
   2    Copyright (C) 1995 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
  16 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 #ifdef HAVE_VALUES_H
  19 # include <values.h>
  20 #endif
  21
  22 /* @@ end of prolog @@ */
  23
  24 #ifndef BITSPERBYTE
  25 # define BITSPERBYTE 8
  26 #endif
  27
  28 #ifndef LONGBITS
  29 # define LONGBITS (sizeof (long) * BITSPERBYTE)
  30 #endif  /* LONGBITS  */
  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 inline unsigned long
  36 hash_string (str_param)
  37      const char *str_param;
  38 {
  39   unsigned long hval, g;
  40   const char *str = str_param;
  41
  42   /* Compute the hash value for the given string.  */
  43   hval = 0;
  44   while (*str != '\0')
  45     {
  46       hval <<= 4;
  47       hval += (unsigned long) *str++;
  48       g = hval & ((unsigned long) 0xf << (LONGBITS - 4));
  49       if (g != 0)
  50         {
  51           hval ^= g >> (LONGBITS - 8);
  52           hval ^= g;
  53         }
  54     }
  55   return hval;
  56 }