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., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #ifdef HAVE_VALUES_H
  20 # include <values.h>
  21 #endif
  22
  23 /* @@ end of prolog @@ */
  24
  25 #ifndef PARAMS
  26 # if __STDC__
  27 #  define PARAMS(Args) Args
  28 # else
  29 #  define PARAMS(Args) ()
  30 # endif
  31 #endif
  32
  33 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  34 #define HASHWORDBITS 32
  35
  36
  37 /* Defines the so called `hashpjw' function by P.J. Weinberger
  38    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  39    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  40 static unsigned long hash_string PARAMS ((const char *__str_param));
  41
  42 static inline unsigned long
  43 hash_string (str_param)
  44      const char *str_param;
  45 {
  46   unsigned long int hval, g;
  47   const char *str = str_param;
  48
  49   /* Compute the hash value for the given string.  */
  50   hval = 0;
  51   while (*str != '\0')
  52     {
  53       hval <<= 4;
  54       hval += (unsigned long) *str++;
  55       g = hval & ((unsigned long) 0xf << (HASHWORDBITS - 4));
  56       if (g != 0)
  57         {
  58           hval ^= g >> (HASHWORDBITS - 8);
  59           hval ^= g;
  60         }
  61     }
  62   return hval;
  63 }