random.c revision 92913
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.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 *	@(#)random.c	8.1 (Berkeley) 6/10/93
34 */
35
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD: head/lib/libstand/random.c 92913 2002-03-21 23:39:28Z obrien $");
38
39#include <sys/types.h>
40
41static u_long randseed = 1;
42
43void
44srandom(seed)
45	u_long seed;
46{
47	randseed = seed;
48}
49
50/*
51 * Pseudo-random number generator for randomizing the profiling clock,
52 * and whatever else we might use it for.  The result is uniform on
53 * [0, 2^31 - 1].
54 */
55u_long
56random()
57{
58	long x, hi, lo, t;
59
60	/*
61	 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
62	 * From "Random number generators: good ones are hard to find",
63	 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
64	 * October 1988, p. 1195.
65	 */
66	x = randseed;
67	hi = x / 127773;
68	lo = x % 127773;
69	t = 16807 * lo - 2836 * hi;
70	if (t <= 0)
71		t += 0x7fffffff;
72	randseed = t;
73	return (t);
74}
75