locale/strlen-hash.h

   1 /* Implements hashing function for string with known length.
   2    Copyright (C) 1996, 1997 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <sys/types.h>
  22
  23 /* We assume to have `size_t' value with at least 32 bits.  */
  24 #define HASHWORDBITS 32
  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 static size_t hash_string (const char *__str_param, size_t __len);
  31
  32 static inline size_t
  33 hash_string (const char *str_param, size_t len)
  34 {
  35   size_t hval, g;
  36   const char *end_str = str_param + len;
  37
  38   /* Compute the hash value for the given string.  */
  39   hval = len;
  40   while (str_param != end_str)
  41     {
  42       hval <<= 4;
  43       hval += (size_t) *str_param++;
  44       g = hval & ((size_t) 0xf << (HASHWORDBITS - 4));
  45       if (g != 0)
  46         {
  47           hval ^= g >> (HASHWORDBITS - 8);
  48           hval ^= g;
  49         }
  50     }
  51   return hval;
  52 }