rand.c revision 85752 
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: head/lib/libc/stdlib/rand.c 85752 2001-10-30 21:26:50Z markm $
36 */
37
38#if defined(LIBC_SCCS) && !defined(lint)
39static 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
53static int
54do_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
84int
85rand_r(unsigned int *ctx)
86{
87	u_long val = (u_long) *ctx;
88	*ctx = do_rand(&val);
89	return (int) *ctx;
90}
91
92
93static u_long next = 1;
94
95int
96rand()
97{
98	return do_rand(&next);
99}
100
101void
102srand(seed)
103u_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 */
116void
117sranddev()
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
141main()
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