locale/strlen-hash.h

   1 /* Implements hashing function for string with known length.
   2    Copyright (C) 1996-2019 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, see
  18    <https://www.gnu.org/licenses/>.  */
  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 }