1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1990, 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 * 3. 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 * Posix rand_r function added May 1999 by Wes Peters <[email protected]>.
32 */
33
34 #if defined(LIBC_SCCS) && !defined(lint)
35 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93";
36 #endif /* LIBC_SCCS and not lint */
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD$");
39
40 #include "namespace.h"
41 #include <sys/param.h>
42 #include <sys/sysctl.h>
43 #include <stdlib.h>
44 #include "un-namespace.h"
45
46 #ifdef TEST
47 #include <stdio.h>
48 #endif /* TEST */
49
50 static int
do_rand(unsigned long * ctx)51 do_rand(unsigned long *ctx)
52 {
53 /*
54 * Compute x = (7^5 * x) mod (2^31 - 1)
55 * without overflowing 31 bits:
56 * (2^31 - 1) = 127773 * (7^5) + 2836
57 * From "Random number generators: good ones are hard to find",
58 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
59 * October 1988, p. 1195.
60 */
61 long hi, lo, x;
62
63 /* Transform to [1, 0x7ffffffe] range. */
64 x = (*ctx % 0x7ffffffe) + 1;
65 hi = x / 127773;
66 lo = x % 127773;
67 x = 16807 * lo - 2836 * hi;
68 if (x < 0)
69 x += 0x7fffffff;
70 /* Transform to [0, 0x7ffffffd] range. */
71 x--;
72 *ctx = x;
73 return (x);
74 }
75
76
77 int
rand_r(unsigned * ctx)78 rand_r(unsigned *ctx)
79 {
80 u_long val;
81 int r;
82
83 val = *ctx;
84 r = do_rand(&val);
85 *ctx = (unsigned)val;
86 return (r);
87 }
88
89
90 static u_long next = 1;
91
92 int
rand(void)93 rand(void)
94 {
95 return (do_rand(&next));
96 }
97
98 void
srand(unsigned seed)99 srand(unsigned seed)
100 {
101 next = seed;
102 }
103
104
105 /*
106 * sranddev:
107 *
108 * Many programs choose the seed value in a totally predictable manner.
109 * This often causes problems. We seed the generator using pseudo-random
110 * data from the kernel.
111 */
112 void
sranddev(void)113 sranddev(void)
114 {
115 int mib[2];
116 size_t len;
117
118 len = sizeof(next);
119
120 mib[0] = CTL_KERN;
121 mib[1] = KERN_ARND;
122 sysctl(mib, 2, (void *)&next, &len, NULL, 0);
123 }
124
125
126 #ifdef TEST
127
main()128 main()
129 {
130 int i;
131 unsigned myseed;
132
133 printf("seeding rand with 0x19610910: \n");
134 srand(0x19610910);
135
136 printf("generating three pseudo-random numbers:\n");
137 for (i = 0; i < 3; i++)
138 {
139 printf("next random number = %d\n", rand());
140 }
141
142 printf("generating the same sequence with rand_r:\n");
143 myseed = 0x19610910;
144 for (i = 0; i < 3; i++)
145 {
146 printf("next random number = %d\n", rand_r(&myseed));
147 }
148
149 return 0;
150 }
151
152 #endif /* TEST */
153
154