44 lines
1.6 KiB
C
44 lines
1.6 KiB
C
/* Implement simple hashing table with string based keys.
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Copyright (C) 1994-1997, 2000, 2001, 2002 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef hashval_t
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# define hashval_t unsigned long int
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#endif
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#include <limits.h> /* For CHAR_BIT. */
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hashval_t
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compute_hashval (const void *key, size_t keylen)
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{
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size_t cnt;
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hashval_t hval;
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/* Compute the hash value for the given string. The algorithm
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is taken from [Aho,Sethi,Ullman], modified to reduce the number of
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collisions for short strings with very varied bit patterns.
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See http://www.clisp.org/haible/hashfunc.html. */
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cnt = 0;
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hval = keylen;
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while (cnt < keylen)
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{
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hval = (hval << 9) | (hval >> (sizeof hval * CHAR_BIT - 9));
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hval += (hashval_t) *(((char *) key) + cnt++);
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}
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return hval != 0 ? hval : ~((hashval_t) 0);
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}
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