xref: /freebsd/lib/libc/stdlib/rand.c (revision a220d00e74dd245b4fca59c5eca0c53963686325)
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. All advertising materials mentioning features or use of this software
14  *    must display the following acknowledgement:
15  *	This product includes software developed by the University of
16  *	California, Berkeley and its contributors.
17  * 4. Neither the name of the University nor the names of its contributors
18  *    may be used to endorse or promote products derived from this software
19  *    without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
34  *
35  * $FreeBSD$
36  */
37 
38 #if defined(LIBC_SCCS) && !defined(lint)
39 static char sccsid[] = "@(#)rand.c	8.1 (Berkeley) 6/14/93";
40 #endif /* LIBC_SCCS and not lint */
41 
42 #include <sys/time.h>          /* for sranddev() */
43 #include <sys/types.h>
44 #include <fcntl.h>             /* for sranddev() */
45 #include <stdlib.h>
46 #include <unistd.h>            /* for sranddev() */
47 #include "un-namespace.h"
48 
49 #ifdef TEST
50 #include <stdio.h>
51 #endif /* TEST */
52 
53 static int
54 do_rand(unsigned long *ctx)
55 {
56 #ifdef  USE_WEAK_SEEDING
57 /*
58  * Historic implementation compatibility.
59  * The random sequences do not vary much with the seed,
60  * even with overflowing.
61  */
62 	return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
63 #else   /* !USE_WEAK_SEEDING */
64 /*
65  * Compute x = (7^5 * x) mod (2^31 - 1)
66  * wihout overflowing 31 bits:
67  *      (2^31 - 1) = 127773 * (7^5) + 2836
68  * From "Random number generators: good ones are hard to find",
69  * Park and Miller, Communications of the ACM, vol. 31, no. 10,
70  * October 1988, p. 1195.
71  */
72 	long hi, lo, x;
73 
74 	hi = *ctx / 127773;
75 	lo = *ctx % 127773;
76 	x = 16807 * lo - 2836 * hi;
77 	if (x <= 0)
78 		x += 0x7fffffff;
79 	return ((*ctx = x) % ((u_long)RAND_MAX + 1));
80 #endif  /* !USE_WEAK_SEEDING */
81 }
82 
83 
84 int
85 rand_r(unsigned int *ctx)
86 {
87 	u_long val = (u_long) *ctx;
88 	*ctx = do_rand(&val);
89 	return (int) *ctx;
90 }
91 
92 
93 static u_long next = 1;
94 
95 int
96 rand()
97 {
98 	return do_rand(&next);
99 }
100 
101 void
102 srand(seed)
103 u_int seed;
104 {
105 	next = seed;
106 }
107 
108 
109 /*
110  * sranddev:
111  *
112  * Many programs choose the seed value in a totally predictable manner.
113  * This often causes problems.  We seed the generator using the much more
114  * secure random(4) interface.
115  */
116 void
117 sranddev()
118 {
119 	int fd, done;
120 
121 	done = 0;
122 	fd = _open("/dev/random", O_RDONLY, 0);
123 	if (fd >= 0) {
124 		if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
125 			done = 1;
126 		_close(fd);
127 	}
128 
129 	if (!done) {
130 		struct timeval tv;
131 		unsigned long junk;
132 
133 		gettimeofday(&tv, NULL);
134 		next = (getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk;
135 	}
136 }
137 
138 
139 #ifdef TEST
140 
141 main()
142 {
143     int i;
144     unsigned myseed;
145 
146     printf("seeding rand with 0x19610910: \n");
147     srand(0x19610910);
148 
149     printf("generating three pseudo-random numbers:\n");
150     for (i = 0; i < 3; i++)
151     {
152 	printf("next random number = %d\n", rand());
153     }
154 
155     printf("generating the same sequence with rand_r:\n");
156     myseed = 0x19610910;
157     for (i = 0; i < 3; i++)
158     {
159 	printf("next random number = %d\n", rand_r(&myseed));
160     }
161 
162     return 0;
163 }
164 
165 #endif /* TEST */
166 
167