63 lines
2.0 KiB
C
63 lines
2.0 KiB
C
/* hashcode-string1.c -- compute a hash value from a NUL-terminated string.
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Copyright (C) 1998-2004, 2006-2007, 2009-2026 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file 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
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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/* Specification. */
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#include "hashcode-string1.h"
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#if USE_DIFF_HASH
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# include "bitrotate.h"
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/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
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B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
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Software--practice & experience 20, 2 (Feb 1990), 209-224. Good hash
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algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
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may not be good for your application." */
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size_t
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hash_string (const char *string, size_t tablesize)
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{
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size_t value = 0;
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unsigned char ch;
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for (; (ch = *string); string++)
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value = ch + rotl_sz (value, 7);
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return value % tablesize;
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}
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#else /* not USE_DIFF_HASH */
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/* This one comes from 'recode', and performs a bit better than the above as
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per a few experiments. It is inspired from a hashing routine found in the
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very old Cyber 'snoop', itself written in typical Greg Mansfield style.
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(By the way, what happened to this excellent man? Is he still alive?) */
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size_t
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hash_string (const char *string, size_t tablesize)
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{
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size_t value = 0;
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unsigned char ch;
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for (; (ch = *string); string++)
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value = (value * 31 + ch) % tablesize;
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return value;
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}
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#endif /* not USE_DIFF_HASH */
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