1/*-
2 * Copyright (c) 1990, 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. 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 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
30 */
31
32#if defined(LIBC_SCCS) && !defined(lint)
33static char sccsid[] = "@(#)rand.c	8.1 (Berkeley) 6/14/93";
34#endif /* LIBC_SCCS and not lint */
35#include <sys/cdefs.h>
36__FBSDID("$FreeBSD$");
37
38#include "namespace.h"
39#include <sys/param.h>
40#include <sys/sysctl.h>
41#include <stdlib.h>
42#include "un-namespace.h"
43
44#ifdef TEST
45#include <stdio.h>
46#endif /* TEST */
47
48static int
49do_rand(unsigned long *ctx)
50{
51/*
52 * Compute x = (7^5 * x) mod (2^31 - 1)
53 * without overflowing 31 bits:
54 *      (2^31 - 1) = 127773 * (7^5) + 2836
55 * From "Random number generators: good ones are hard to find",
56 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
57 * October 1988, p. 1195.
58 */
59	long hi, lo, x;
60
61	/* Transform to [1, 0x7ffffffe] range. */
62	x = (*ctx % 0x7ffffffe) + 1;
63	hi = x / 127773;
64	lo = x % 127773;
65	x = 16807 * lo - 2836 * hi;
66	if (x < 0)
67		x += 0x7fffffff;
68	/* Transform to [0, 0x7ffffffd] range. */
69	x--;
70	*ctx = x;
71	return (x);
72}
73
74
75int
76rand_r(unsigned *ctx)
77{
78	u_long val;
79	int r;
80
81	val = *ctx;
82	r = do_rand(&val);
83	*ctx = (unsigned)val;
84	return (r);
85}
86
87
88static u_long next = 1;
89
90int
91rand(void)
92{
93	return (do_rand(&next));
94}
95
96void
97srand(unsigned seed)
98{
99	next = seed;
100}
101
102
103/*
104 * sranddev:
105 *
106 * Many programs choose the seed value in a totally predictable manner.
107 * This often causes problems.  We seed the generator using pseudo-random
108 * data from the kernel.
109 */
110void
111sranddev(void)
112{
113	int mib[2];
114	size_t len;
115
116	len = sizeof(next);
117
118	mib[0] = CTL_KERN;
119	mib[1] = KERN_ARND;
120	sysctl(mib, 2, (void *)&next, &len, NULL, 0);
121}
122
123
124#ifdef TEST
125
126main()
127{
128    int i;
129    unsigned myseed;
130
131    printf("seeding rand with 0x19610910: \n");
132    srand(0x19610910);
133
134    printf("generating three pseudo-random numbers:\n");
135    for (i = 0; i < 3; i++)
136    {
137	printf("next random number = %d\n", rand());
138    }
139
140    printf("generating the same sequence with rand_r:\n");
141    myseed = 0x19610910;
142    for (i = 0; i < 3; i++)
143    {
144	printf("next random number = %d\n", rand_r(&myseed));
145    }
146
147    return 0;
148}
149
150#endif /* TEST */
151
152