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)
33 static 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 <sys/types.h>
42 #include <stdlib.h>
43 #include "un-namespace.h"
44
45 #ifdef TEST
46 #include <stdio.h>
47 #endif /* TEST */
48
49 static int
do_rand(unsigned long * ctx)50 do_rand(unsigned long *ctx)
51 {
52 #ifdef USE_WEAK_SEEDING
53 /*
54 * Historic implementation compatibility.
55 * The random sequences do not vary much with the seed,
56 * even with overflowing.
57 */
58 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
59 #else /* !USE_WEAK_SEEDING */
60 /*
61 * Compute x = (7^5 * x) mod (2^31 - 1)
62 * without overflowing 31 bits:
63 * (2^31 - 1) = 127773 * (7^5) + 2836
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 long hi, lo, x;
69
70 /* Must be in [1, 0x7ffffffe] range at this point. */
71 hi = *ctx / 127773;
72 lo = *ctx % 127773;
73 x = 16807 * lo - 2836 * hi;
74 if (x < 0)
75 x += 0x7fffffff;
76 *ctx = x;
77 /* Transform to [0, 0x7ffffffd] range. */
78 return (x - 1);
79 #endif /* !USE_WEAK_SEEDING */
80 }
81
82
83 int
rand_r(unsigned int * ctx)84 rand_r(unsigned int *ctx)
85 {
86 u_long val;
87 int r;
88
89 #ifdef USE_WEAK_SEEDING
90 val = *ctx;
91 #else
92 /* Transform to [1, 0x7ffffffe] range. */
93 val = (*ctx % 0x7ffffffe) + 1;
94 #endif
95 r = do_rand(&val);
96
97 #ifdef USE_WEAK_SEEDING
98 *ctx = (unsigned int)val;
99 #else
100 *ctx = (unsigned int)(val - 1);
101 #endif
102 return (r);
103 }
104
105
106 static u_long next =
107 #ifdef USE_WEAK_SEEDING
108 1;
109 #else
110 2;
111 #endif
112
113 int
rand()114 rand()
115 {
116 return (do_rand(&next));
117 }
118
119 void
srand(seed)120 srand(seed)
121 u_int seed;
122 {
123 next = seed;
124 #ifndef USE_WEAK_SEEDING
125 /* Transform to [1, 0x7ffffffe] range. */
126 next = (next % 0x7ffffffe) + 1;
127 #endif
128 }
129
130
131 /*
132 * sranddev:
133 *
134 * Many programs choose the seed value in a totally predictable manner.
135 * This often causes problems. We seed the generator using pseudo-random
136 * data from the kernel.
137 */
138 void
sranddev()139 sranddev()
140 {
141 int mib[2];
142 size_t len;
143
144 len = sizeof(next);
145
146 mib[0] = CTL_KERN;
147 mib[1] = KERN_ARND;
148 sysctl(mib, 2, (void *)&next, &len, NULL, 0);
149 #ifndef USE_WEAK_SEEDING
150 /* Transform to [1, 0x7ffffffe] range. */
151 next = (next % 0x7ffffffe) + 1;
152 #endif
153 }
154
155
156 #ifdef TEST
157
main()158 main()
159 {
160 int i;
161 unsigned myseed;
162
163 printf("seeding rand with 0x19610910: \n");
164 srand(0x19610910);
165
166 printf("generating three pseudo-random numbers:\n");
167 for (i = 0; i < 3; i++)
168 {
169 printf("next random number = %d\n", rand());
170 }
171
172 printf("generating the same sequence with rand_r:\n");
173 myseed = 0x19610910;
174 for (i = 0; i < 3; i++)
175 {
176 printf("next random number = %d\n", rand_r(&myseed));
177 }
178
179 return 0;
180 }
181
182 #endif /* TEST */
183
184