intl/hash-string.c

   1 /* Implements a string hashing function.
   2    Copyright (C) 1995-2013 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 #include "hash-string.h"
  20
  21
  22 /* Defines the so called `hashpjw' function by P.J. Weinberger
  23    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  24    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  25 unsigned long int
  26 __hash_string (str_param)
  27      const char *str_param;
  28 {
  29   unsigned long int hval, g;
  30   const char *str = str_param;
  31
  32   /* Compute the hash value for the given string.  */
  33   hval = 0;
  34   while (*str != '\0')
  35     {
  36       hval <<= 4;
  37       hval += (unsigned char) *str++;
  38       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  39       if (g != 0)
  40         {
  41           hval ^= g >> (HASHWORDBITS - 8);
  42           hval ^= g;
  43         }
  44     }
  45   return hval;
  46 }