intl/hash-string.h

   1 /* Implements a string hashing function.
   2    Copyright (C) 1995, 1997 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 Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
  17    Boston, MA 02110-1301, USA.  */
  18
  19 /* @@ end of prolog @@ */
  20
  21 #ifndef PARAMS
  22 # if __STDC__
  23 #  define PARAMS(Args) Args
  24 # else
  25 #  define PARAMS(Args) ()
  26 # endif
  27 #endif
  28
  29 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  30 #define HASHWORDBITS 32
  31
  32
  33 /* Defines the so called `hashpjw' function by P.J. Weinberger
  34    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  35    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  36 static unsigned long hash_string PARAMS ((const char *__str_param));
  37
  38 static inline unsigned long
  39 hash_string (str_param)
  40      const char *str_param;
  41 {
  42   unsigned long int hval, g;
  43   const char *str = str_param;
  44
  45   /* Compute the hash value for the given string.  */
  46   hval = 0;
  47   while (*str != '\0')
  48     {
  49       hval <<= 4;
  50       hval += (unsigned long) *str++;
  51       g = hval & ((unsigned long) 0xf << (HASHWORDBITS - 4));
  52       if (g != 0)
  53         {
  54           hval ^= g >> (HASHWORDBITS - 8);
  55           hval ^= g;
  56         }
  57     }
  58   return hval;
  59 }