42 lines
1.6 KiB
C
42 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, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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unsigned long
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compute_hashval (key, keylen)
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const void *key;
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size_t keylen;
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{
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size_t cnt;
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unsigned long int 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 >> (LONGBITS - 9));
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hval += (unsigned long int) *(((char *) key) + cnt++);
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}
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return hval != 0 ? hval : ~((unsigned long) 0);
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}
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