1  /* hash-pjw.c -- compute a hash value from a NUL-terminated string.
       2  
       3     Copyright (C) 2001, 2003, 2006, 2009-2021 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  }