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 * 4. Neither the name of the University nor the names of its contributors
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 */
31
32#include <sys/cdefs.h>
33__FBSDID("$FreeBSD: stable/11/sys/libkern/random.c 319284 2017-05-31 05:45:06Z delphij $");
34
35#include <sys/libkern.h>
36
37#define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
38
39static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
40
41void
42srandom(seed)
43	u_long seed;
44{
45	int i;
46
47	randseed = seed;
48	for (i = 0; i < NSHUFF; i++)
49		(void)random();
50}
51
52/*
53 * Pseudo-random number generator for perturbing the profiling clock,
54 * and whatever else we might use it for.  The result is uniform on
55 * [0, 2^31 - 1].
56 */
57u_long
58random()
59{
60	long x, hi, lo, t;
61
62	/*
63	 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
64	 * From "Random number generators: good ones are hard to find",
65	 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
66	 * October 1988, p. 1195.
67	 */
68	/* Can't be initialized with 0, so use another value. */
69	if ((x = randseed) == 0)
70		x = 123459876;
71	hi = x / 127773;
72	lo = x % 127773;
73	t = 16807 * lo - 2836 * hi;
74	if (t < 0)
75		t += 0x7fffffff;
76	randseed = t;
77	return (t);
78}
79