random.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
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 * 4. 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 <sys/cdefs.h>
35__FBSDID("$FreeBSD: stable/11/sys/libkern/random.c 330897 2018-03-14 03:19:51Z eadler $");
36
37#include <sys/libkern.h>
38
39#define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
40
41static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
42
43void
44srandom(seed)
45	u_long seed;
46{
47	int i;
48
49	randseed = seed;
50	for (i = 0; i < NSHUFF; i++)
51		(void)random();
52}
53
54/*
55 * Pseudo-random number generator for perturbing the profiling clock,
56 * and whatever else we might use it for.  The result is uniform on
57 * [0, 2^31 - 1].
58 */
59u_long
60random()
61{
62	long x, hi, lo, t;
63
64	/*
65	 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
66	 * From "Random number generators: good ones are hard to find",
67	 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
68	 * October 1988, p. 1195.
69	 */
70	/* Can't be initialized with 0, so use another value. */
71	if ((x = randseed) == 0)
72		x = 123459876;
73	hi = x / 127773;
74	lo = x % 127773;
75	t = 16807 * lo - 2836 * hi;
76	if (t < 0)
77		t += 0x7fffffff;
78	randseed = t;
79	return (t);
80}
81