lib/hash-pjw.c

   1 /* hash-pjw.c -- compute a hash value from a NUL-terminated string.
   2
   3    Copyright (C) 2001, 2003, 2006, 2009-2020 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 #include "hash-pjw.h"
  21
  22 #include <limits.h>
  23
  24 #define SIZE_BITS (sizeof (size_t) * CHAR_BIT)
  25
  26 /* A hash function for NUL-terminated char* strings using
  27    the method described by Bruno Haible.
  28    See https://www.haible.de/bruno/hashfunc.html.  */
  29
  30 size_t
  31 hash_pjw (const void *x, size_t tablesize)
  32 {
  33   const char *s;
  34   size_t h = 0;
  35
  36   for (s = x; *s; s++)
  37     h = *s + ((h << 9) | (h >> (SIZE_BITS - 9)));
  38
  39   return h % tablesize;
  40 }