intl/hash-string.c

   1 /* Implements a string hashing function.
   2    Copyright (C) 1995-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #ifdef HAVE_CONFIG_H
  20 # include <config.h>
  21 #endif
  22
  23 /* Specification.  */
  24 #include "hash-string.h"
  25
  26
  27 /* Defines the so called `hashpjw' function by P.J. Weinberger
  28    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  29    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  30 unsigned long int
  31 __hash_string (const char *str_param)
  32 {
  33   unsigned long int hval, g;
  34   const char *str = str_param;
  35
  36   /* Compute the hash value for the given string.  */
  37   hval = 0;
  38   while (*str != '\0')
  39     {
  40       hval <<= 4;
  41       hval += (unsigned char) *str++;
  42       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  43       if (g != 0)
  44         {
  45           hval ^= g >> (HASHWORDBITS - 8);
  46           hval ^= g;
  47         }
  48     }
  49   return hval;
  50 }