rand.c revision 110236 
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
36#if defined(LIBC_SCCS) && !defined(lint)
37static char sccsid[] = "@(#)rand.c	8.1 (Berkeley) 6/14/93";
38#endif /* LIBC_SCCS and not lint */
39#include <sys/cdefs.h>
40__FBSDID("$FreeBSD: head/lib/libc/stdlib/rand.c 110236 2003-02-02 14:27:51Z ache $");
41
42#include "namespace.h"
43#include <sys/time.h>          /* for sranddev() */
44#include <sys/types.h>
45#include <fcntl.h>             /* for sranddev() */
46#include <stdlib.h>
47#include <unistd.h>            /* for sranddev() */
48#include "un-namespace.h"
49
50#ifdef TEST
51#include <stdio.h>
52#endif /* TEST */
53
54static int
55do_rand(unsigned long *ctx)
56{
57#ifdef  USE_WEAK_SEEDING
58/*
59 * Historic implementation compatibility.
60 * The random sequences do not vary much with the seed,
61 * even with overflowing.
62 */
63	return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
64#else   /* !USE_WEAK_SEEDING */
65/*
66 * Compute x = (7^5 * x) mod (2^31 - 1)
67 * wihout overflowing 31 bits:
68 *      (2^31 - 1) = 127773 * (7^5) + 2836
69 * From "Random number generators: good ones are hard to find",
70 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
71 * October 1988, p. 1195.
72 */
73	long hi, lo, x;
74
75	hi = *ctx / 127773;
76	lo = *ctx % 127773;
77	x = 16807 * lo - 2836 * hi;
78	if (x <= 0)
79		x += 0x7fffffff;
80	return ((*ctx = x) % ((u_long)RAND_MAX + 1));
81#endif  /* !USE_WEAK_SEEDING */
82}
83
84
85int
86rand_r(unsigned int *ctx)
87{
88	u_long val = (u_long) *ctx;
89	int r = do_rand(&val);
90
91	*ctx = (unsigned int) val;
92	return (r);
93}
94
95
96static u_long next = 1;
97
98int
99rand()
100{
101	return do_rand(&next);
102}
103
104void
105srand(seed)
106u_int seed;
107{
108	next = seed;
109}
110
111
112/*
113 * sranddev:
114 *
115 * Many programs choose the seed value in a totally predictable manner.
116 * This often causes problems.  We seed the generator using the much more
117 * secure random(4) interface.
118 */
119void
120sranddev()
121{
122	int fd, done;
123
124	done = 0;
125	fd = _open("/dev/random", O_RDONLY, 0);
126	if (fd >= 0) {
127		if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
128			done = 1;
129		_close(fd);
130	}
131
132	if (!done) {
133		struct timeval tv;
134		unsigned long junk;
135
136		gettimeofday(&tv, NULL);
137		next = (getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk;
138	}
139}
140
141
142#ifdef TEST
143
144main()
145{
146    int i;
147    unsigned myseed;
148
149    printf("seeding rand with 0x19610910: \n");
150    srand(0x19610910);
151
152    printf("generating three pseudo-random numbers:\n");
153    for (i = 0; i < 3; i++)
154    {
155	printf("next random number = %d\n", rand());
156    }
157
158    printf("generating the same sequence with rand_r:\n");
159    myseed = 0x19610910;
160    for (i = 0; i < 3; i++)
161    {
162	printf("next random number = %d\n", rand_r(&myseed));
163    }
164
165    return 0;
166}
167
168#endif /* TEST */
169
170