/* 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 <email@example.com>, 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
# define hashval_t unsigned long int
#include <limits.h> /* For CHAR_BIT. */
compute_hashval (const void *key, size_t keylen)
/* 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);