Remove wrong getvfsbytype.3 MLINK. The manpage doesn't document it.
[dragonfly.git] / sys / libkern / random.c
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1/*-
2 * Copyright (c) 1992, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
dc71b7ab 13 * 3. Neither the name of the University nor the names of its contributors
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14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * @(#)random.c 8.1 (Berkeley) 6/10/93
30 * $FreeBSD: src/sys/libkern/random.c,v 1.7 1999/08/28 00:46:36 peter Exp $
cddfb7bb 31 * $DragonFly: src/sys/libkern/random.c,v 1.6 2006/09/03 18:52:29 dillon Exp $
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32 */
33
34#include <sys/libkern.h>
35
36static u_long randseed = 1;
37
38void
cddfb7bb 39skrandom(u_long seed)
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40{
41 randseed = seed;
42}
43
44/*
45 * Pseudo-random number generator for randomizing the profiling clock,
46 * and whatever else we might use it for. The result is uniform on
47 * [0, 2^31 - 1].
48 */
49u_long
cddfb7bb 50krandom(void)
984263bc 51{
0e99e805 52 long x, hi, lo, t;
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53
54 /*
55 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
56 * From "Random number generators: good ones are hard to find",
57 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
58 * October 1988, p. 1195.
59 */
60 x = randseed;
61 hi = x / 127773;
62 lo = x % 127773;
63 t = 16807 * lo - 2836 * hi;
64 if (t <= 0)
65 t += 0x7fffffff;
66 randseed = t;
67 return (t);
68}