1 /* $OpenBSD: random.c,v 1.10 2017/09/08 05:36:53 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/param.h>
36
37 #include <lib/libkern/libkern.h>
38
39 /*
40 * Pseudo-random number generator for randomizing the profiling clock.
41 * The result is uniform on [0, 2^31 - 1].
42 */
43
44 u_int32_t
random(void)45 random(void)
46 {
47 struct cpu_info *ci = curcpu();
48 int32_t x, hi, lo, t;
49
50 /*
51 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
52 * From "Random number generators: good ones are hard to find",
53 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
54 * October 1988, p. 1195.
55 */
56 x = ci->ci_randseed;
57 hi = x / 127773;
58 lo = x % 127773;
59 t = 16807 * lo - 2836 * hi;
60 if (t <= 0)
61 t += 0x7fffffff;
62 ci->ci_randseed = t;
63 return (t);
64 }
65