intl/hash-string.h

   1 /* hash-string - Implements a string hashing function.
   2    Copyright (C) 1995 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
  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 PARAMS
  25 # if __STDC__
  26 #  define PARAMS(Args) Args
  27 # else
  28 #  define PARAMS(Args) ()
  29 # endif
  30 #endif
  31
  32 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  33 #define HASHWORDBITS 32
  34
  35
  36 /* Defines the so called `hashpjw' function by P.J. Weinberger
  37    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  38    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  39 static unsigned long hash_string PARAMS ((const char *__str_param));
  40
  41 static inline unsigned long
  42 hash_string (str_param)
  43      const char *str_param;
  44 {
  45   unsigned long int hval, g;
  46   const char *str = str_param;
  47
  48   /* Compute the hash value for the given string.  */
  49   hval = 0;
  50   while (*str != '\0')
  51     {
  52       hval <<= 4;
  53       hval += (unsigned long) *str++;
  54       g = hval & ((unsigned long) 0xf << (HASHWORDBITS - 4));
  55       if (g != 0)
  56         {
  57           hval ^= g >> (HASHWORDBITS - 8);
  58           hval ^= g;
  59         }
  60     }
  61   return hval;
  62 }