1 /* hash.c - The gdbm hash function. */
3 /* This file is part of GDBM, the GNU data base manager.
4 Copyright (C) 1990, 1991, 1993, 2007, 2011, 2013 Free Software Foundation,
7 GDBM is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3, or (at your option)
12 GDBM is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GDBM. If not, see <http://www.gnu.org/licenses/>. */
20 /* Include system configuration before all else. */
26 /* This hash function computes a 31 bit value. The value is used to index
27 the hash directory using the top n bits. It is also used in a hash bucket
28 to find the home position of the element by taking the value modulo the
29 bucket hash table size. */
32 _gdbm_hash (datum key)
34 unsigned int value; /* Used to compute the hash value. */
35 int index; /* Used to cycle through random values. */
38 /* Set the initial value from key. */
39 value = 0x238F13AF * key.dsize;
40 for (index = 0; index < key.dsize; index++)
41 value = (value + (key.dptr[index] << (index*5 % 24))) & 0x7FFFFFFF;
43 value = (1103515243 * value + 12345) & 0x7FFFFFFF;
45 /* Return the value. */