intl/hash-string.h

   1 /* hash-string - Implements a string hashing function.
   2    Copyright (C) 1995 Free Software Foundation, Inc.
   3
   4 This file is part of the GNU C Library.  Its master source is NOT part of
   5 the C library, however.  The master source lives in /gd/gnu/lib.
   6
   7 The GNU C Library is free software; you can redistribute it and/or
   8 modify it under the terms of the GNU Library General Public License as
   9 published by the Free Software Foundation; either version 2 of the
  10 License, or (at your option) any later version.
  11
  12 The GNU C Library is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 Library General Public License for more details.
  16
  17 You should have received a copy of the GNU Library General Public
  18 License along with the GNU C Library; see the file COPYING.LIB.  If
  19 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  20 Cambridge, MA 02139, USA.  */
  21
  22 #ifdef HAVE_VALUES_H
  23 # include <values.h>
  24 #endif
  25
  26 /* @@ end of prolog @@ */
  27
  28 #ifndef PARAMS
  29 # if __STDC__
  30 #  define PARAMS(Args) Args
  31 # else
  32 #  define PARAMS(Args) ()
  33 # endif
  34 #endif
  35
  36 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  37 #define HASHWORDBITS 32
  38
  39
  40 /* Defines the so called `hashpjw' function by P.J. Weinberger
  41    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  42    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  43 static unsigned long hash_string PARAMS ((const char *__str_param));
  44
  45 static inline unsigned long
  46 hash_string (str_param)
  47      const char *str_param;
  48 {
  49   unsigned long int hval, g;
  50   const char *str = str_param;
  51
  52   /* Compute the hash value for the given string.  */
  53   hval = 0;
  54   while (*str != '\0')
  55     {
  56       hval <<= 4;
  57       hval += (unsigned long) *str++;
  58       g = hval & ((unsigned long) 0xf << (HASHWORDBITS - 4));
  59       if (g != 0)
  60         {
  61           hval ^= g >> (HASHWORDBITS - 8);
  62           hval ^= g;
  63         }
  64     }
  65   return hval;
  66 }