1  /* hash-pjw-bare.c -- compute a hash value from a provided buffer.
       2  
       3     Copyright (C) 2012-2023 Free Software Foundation, Inc.
       4  
       5     This file is free software: you can redistribute it and/or modify
       6     it under the terms of the GNU Lesser General Public License as
       7     published by the Free Software Foundation; either version 2.1 of the
       8     License, or (at your option) any later version.
       9  
      10     This file 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 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  }