locale/strlen-hash.h

   1 /* strlen-hash - Implements hashing function for string with known length.
   2 Copyright (C) 1996 Free Software Foundation, Inc.
   3 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 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 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18 Boston, MA 02111-1307, USA.  */
  19
  20 #include <sys/types.h>
  21
  22 /* We assume to have `size_t' value with at least 32 bits.  */
  23 #define HASHWORDBITS 32
  24
  25
  26 /* Defines the so called `hashpjw' function by P.J. Weinberger
  27    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  28    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  29 static size_t hash_string (const char *__str_param, size_t __len);
  30
  31 static inline size_t
  32 hash_string (const char *str_param, size_t len)
  33 {
  34   size_t hval, g;
  35   const char *end_str = str_param + len;
  36
  37   /* Compute the hash value for the given string.  */
  38   hval = len;
  39   while (str_param != end_str)
  40     {
  41       hval <<= 4;
  42       hval += (size_t) *str_param++;
  43       g = hval & ((size_t) 0xf << (HASHWORDBITS - 4));
  44       if (g != 0)
  45         {
  46           hval ^= g >> (HASHWORDBITS - 8);
  47           hval ^= g;
  48         }
  49     }
  50   return hval;
  51 }