locale/strlen-hash.h

   1 /* Implements hashing function for string with known length.
   2    Copyright (C) 1996-2023 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <sys/types.h>
  20
  21 /* We assume to have `size_t' value with at least 32 bits.  */
  22 #define HASHWORDBITS 32
  23
  24
  25 /* Defines the so called `hashpjw' function by P.J. Weinberger
  26    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  27    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  28 static size_t hash_string (const char *__str_param, size_t __len);
  29
  30 static inline size_t
  31 hash_string (const char *str_param, size_t len)
  32 {
  33   size_t hval, g;
  34   const char *end_str = str_param + len;
  35
  36   /* Compute the hash value for the given string.  */
  37   hval = len;
  38   while (str_param != end_str)
  39     {
  40       hval <<= 4;
  41       hval += (size_t) *str_param++;
  42       g = hval & ((size_t) 0xf << (HASHWORDBITS - 4));
  43       if (g != 0)
  44         {
  45           hval ^= g >> (HASHWORDBITS - 8);
  46           hval ^= g;
  47         }
  48     }
  49   return hval;
  50 }