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 * @(#)rand.c 8.1 (Berkeley) 6/14/93
32 * $FreeBSD: src/lib/libc/stdlib/rand.c,v 1.17 2007/12/11 20:39:32 ache Exp $
33 */
34
35 #include "namespace.h"
36 #include <sys/time.h> /* for sranddev() */
37 #include <sys/types.h>
38 #include <sys/sysctl.h>
39 #include <fcntl.h> /* for sranddev() */
40 #include <stdlib.h>
41 #include <unistd.h> /* for sranddev() */
42 #include "un-namespace.h"
43
44 #ifdef TEST
45 #include <stdio.h>
46 #endif /* TEST */
47
48 /*
49 * Compute x = (7^5 * x) mod (2^31 - 1)
50 * without overflowing 31 bits:
51 * (2^31 - 1) = 127773 * (7^5) + 2836
52 * From "Random number generators: good ones are hard to find",
53 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
54 * October 1988, p. 1195.
55 */
56 static int
do_rand(unsigned long * ctx)57 do_rand(unsigned long *ctx)
58 {
59 long hi, lo, x;
60
61 /* Can't be initialized with 0, so use another value. */
62 if (*ctx == 0)
63 *ctx = 123459876;
64 hi = *ctx / 127773;
65 lo = *ctx % 127773;
66 x = 16807 * lo - 2836 * hi;
67 if (x < 0)
68 x += 0x7fffffff;
69 return ((*ctx = x) % ((u_long)RAND_MAX + 1));
70 }
71
72
73 int
rand_r(unsigned int * ctx)74 rand_r(unsigned int *ctx)
75 {
76 u_long val = (u_long) *ctx;
77 int r = do_rand(&val);
78
79 *ctx = (unsigned int) val;
80 return (r);
81 }
82
83
84 static u_long next = 1;
85
86 int
rand(void)87 rand(void)
88 {
89 return (do_rand(&next));
90 }
91
92 void
srand(u_int seed)93 srand(u_int seed)
94 {
95 next = seed;
96 }
97
98
99 /*
100 * sranddev:
101 *
102 * Many programs choose the seed value in a totally predictable manner.
103 * This often causes problems. We seed the generator using the much more
104 * secure random(4) interface.
105 */
106 void
sranddev(void)107 sranddev(void)
108 {
109 int fd, done;
110
111 done = 0;
112 fd = _open("/dev/random", O_RDONLY, 0);
113 if (fd >= 0) {
114 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
115 done = 1;
116 _close(fd);
117 }
118
119 if (!done) {
120 size_t len = sizeof(next);
121
122 if (sysctlbyname("kern.random", &next, &len, NULL, 0) == 0)
123 done = 1;
124 }
125
126 if (!done) {
127 struct timeval tv;
128
129 gettimeofday(&tv, NULL);
130 srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec);
131 }
132 }
133
134
135 #ifdef TEST
136
137 int
main(int argc __unused,char * argv[]__unused)138 main(int argc __unused, char *argv[] __unused)
139 {
140 int i;
141 unsigned myseed;
142
143 printf("seeding rand with 0x19610910: \n");
144 srand(0x19610910);
145
146 printf("generating three pseudo-random numbers:\n");
147 for (i = 0; i < 3; i++)
148 {
149 printf("next random number = %d\n", rand());
150 }
151
152 printf("generating the same sequence with rand_r:\n");
153 myseed = 0x19610910;
154 for (i = 0; i < 3; i++)
155 {
156 printf("next random number = %d\n", rand_r(&myseed));
157 }
158
159 return 0;
160 }
161
162 #endif /* TEST */
163
164