1 /* $OpenBSD: random.c,v 1.7 2004/08/07 00:38:33 deraadt Exp $ */
2 /* $NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $ */
3
4 /*-
5 * Copyright (c) 1992, 1993
6 * The Regents of the University of California. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 *
32 * @(#)random.c 8.1 (Berkeley) 6/10/93
33 */
34
35 #include <sys/types.h>
36
37 #include <lib/libkern/libkern.h>
38
39 /*
40 * Pseudo-random number generator for randomizing the profiling clock,
41 * and whatever else we might use it for. The result is uniform on
42 * [0, 2^31 - 1].
43 */
44 u_long _randseed = 1;
45
46 u_long
47 random(void)
48 {
49 long x, hi, lo, t;
50
51 /*
52 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
53 * From "Random number generators: good ones are hard to find",
54 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
55 * October 1988, p. 1195.
56 */
57 x = _randseed;
58 hi = x / 127773;
59 lo = x % 127773;
60 t = 16807 * lo - 2836 * hi;
61 if (t <= 0)
62 t += 0x7fffffff;
63 _randseed = t;
64 return (t);
65 }