lib/hash-pjw-bare.c

   1 /* hash-pjw-bare.c -- compute a hash value from a provided buffer.
   2
   3    Copyright (C) 2012-2020 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify it
   6    under the terms of the GNU Lesser General Public License as published
   7    by 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser 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-bare.h"
  21
  22 #include <limits.h>
  23
  24 #define SIZE_BITS (sizeof (size_t) * CHAR_BIT)
  25
  26 /* Return a hash of the N bytes of X using the method described by
  27    Bruno Haible in https://www.haible.de/bruno/hashfunc.html.
  28    Note that while many hash functions reduce their result via modulo
  29    to a 0..table_size-1 range, this function does not do that.  */
  30
  31 size_t
  32 hash_pjw_bare (const void *x, size_t n)
  33 {
  34   const unsigned char *s = x;
  35   size_t h = 0;
  36   unsigned i;
  37
  38   for (i = 0; i < n; i++)
  39     h = s[i] + ((h << 9) | (h >> (SIZE_BITS - 9)));
  40
  41   return h;
  42 }