/* Implement simple hashing table with string based keys.

   Copyright (C) 1994-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#ifndef hashval_t

# define hashval_t unsigned long int

#endif

#include <limits.h>		/* For CHAR_BIT.  */

hashval_t

compute_hashval (const void *key, size_t keylen)

{

  size_t cnt;

  hashval_t hval;

  /* Compute the hash value for the given string.  The algorithm

     is taken from [Aho,Sethi,Ullman], modified to reduce the number of

     collisions for short strings with very varied bit patterns.

     See http://www.clisp.org/haible/hashfunc.html.  */

  cnt = 0;

  hval = keylen;

  while (cnt < keylen)

    {

      hval = (hval << 9) | (hval >> (sizeof hval * CHAR_BIT - 9));

      hval += (hashval_t) ((const unsigned char *) key)[cnt++];

    }

  return hval != 0 ? hval : ~((hashval_t) 0);

}