1 /* $NetBSD: random.c,v 1.5 2003/08/07 16:32:10 agc Exp $ */
2
3 /*-
4 * Copyright (c) 1992, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 *
31 * @(#)random.c 8.1 (Berkeley) 6/10/93
32 */
33
34 #include <lib/libkern/libkern.h>
35
36 /*
37 * Pseudo-random number generator for randomizing the profiling clock,
38 * and whatever else we might use it for. The result is uniform on
39 * [0, 2^31 - 1].
40 */
41 u_long
42 random()
43 {
44 static u_long randseed = 1;
45 long x, hi, lo, t;
46
47 /*
48 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
49 * From "Random number generators: good ones are hard to find",
50 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
51 * October 1988, p. 1195.
52 */
53 x = randseed;
54 hi = x / 127773;
55 lo = x % 127773;
56 t = 16807 * lo - 2836 * hi;
57 if (t <= 0)
58 t += 0x7fffffff;
59 randseed = t;
60 return (t);
61 }
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