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/* hash.c - The gdbm hash function. */
/* This file is part of GDBM, the GNU data base manager.
Copyright (C) 1990-1991, 1993, 2007, 2011, 2013, 2017-2019 Free
Software Foundation, Inc.
GDBM is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GDBM 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with GDBM. If not, see <http://www.gnu.org/licenses/>. */
/* Include system configuration before all else. */
#include "autoconf.h"
#include "gdbmdefs.h"
/* This hash function computes a GDBM_HASH_BITS-bit value. The value is used
to index the hash directory using the top n bits. It is also used in a
hash bucket to find the home position of the element by taking the value
modulo the bucket hash table size. */
int
_gdbm_hash (datum key)
{
unsigned int value; /* Used to compute the hash value. */
int index; /* Used to cycle through random values. */
/* Set the initial value from key. */
value = 0x238F13AF * key.dsize;
for (index = 0; index < key.dsize; index++)
value = (value + (key.dptr[index] << (index*5 % 24))) & 0x7FFFFFFF;
value = (1103515243 * value + 12345) & 0x7FFFFFFF;
/* Return the value. */
return((int) value);
}
int
_gdbm_bucket_dir (GDBM_FILE dbf, int hash)
{
return hash >> (GDBM_HASH_BITS - dbf->header->dir_bits);
}
void
_gdbm_hash_key (GDBM_FILE dbf, datum key, int *hash, int *bucket, int *offset)
{
int hashval = _gdbm_hash (key);
*hash = hashval;
*bucket = _gdbm_bucket_dir (dbf, hashval);
*offset = hashval % dbf->header->bucket_elems;
}
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