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/* hashcode-string1.c -- compute a hash value from a NUL-terminated string.
Copyright (C) 1998-2004, 2006-2007, 2009-2025 Free Software Foundation, Inc.
This file 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.
This file 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 this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include "hashcode-string1.h"
#if USE_DIFF_HASH
# include "bitrotate.h"
/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
Software--practice & experience 20, 2 (Feb 1990), 209-224. Good hash
algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
may not be good for your application." */
size_t
hash_string (const char *string, size_t tablesize)
{
size_t value = 0;
unsigned char ch;
for (; (ch = *string); string++)
value = ch + rotl_sz (value, 7);
return value % tablesize;
}
#else /* not USE_DIFF_HASH */
/* This one comes from 'recode', and performs a bit better than the above as
per a few experiments. It is inspired from a hashing routine found in the
very old Cyber 'snoop', itself written in typical Greg Mansfield style.
(By the way, what happened to this excellent man? Is he still alive?) */
size_t
hash_string (const char *string, size_t tablesize)
{
size_t value = 0;
unsigned char ch;
for (; (ch = *string); string++)
value = (value * 31 + ch) % tablesize;
return value;
}
#endif /* not USE_DIFF_HASH */
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