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/* Implement simple hashing table with string based keys.
Copyright (C) 1994-1997, 2000, 2001, 2002 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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#ifndef LONGBITS
# include <limits.h>
# define LONGBITS (sizeof (long int) * CHAR_BIT)
#endif
unsigned long int compute_hashval (const void *key, size_t keylen);
unsigned long int
compute_hashval (key, keylen)
const void *key;
size_t keylen;
{
size_t cnt;
unsigned long int 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 >> (LONGBITS - 9));
hval += (unsigned long int) *(((char *) key) + cnt++);
}
return hval != 0 ? hval : ~((unsigned long int) 0);
}
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