libc/stdlib/rand.c

/*-
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)rand.c      8.1 (Berkeley) 6/14/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "namespace.h"
#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/types.h>
#include <stdlib.h>
#include "un-namespace.h"

#ifdef TEST
#include <stdio.h>
#endif /* TEST */

static int
do_rand(unsigned long *ctx)
{
#ifdef  USE_WEAK_SEEDING
/*
 * Historic implementation compatibility.
 * The random sequences do not vary much with the seed,
 * even with overflowing.
 */
        return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
#else   /* !USE_WEAK_SEEDING */
/*
 * Compute x = (7^5 * x) mod (2^31 - 1)
 * without overflowing 31 bits:
 *      (2^31 - 1) = 127773 * (7^5) + 2836
 * From "Random number generators: good ones are hard to find",
 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
 * October 1988, p. 1195.
 */
        long hi, lo, x;

        /* Must be in [1, 0x7ffffffe] range at this point. */
        hi = *ctx / 127773;
        lo = *ctx % 127773;
        x = 16807 * lo - 2836 * hi;
        if (x < 0)
                x += 0x7fffffff;
        *ctx = x;
        /* Transform to [0, 0x7ffffffd] range. */
        return (x - 1);
#endif  /* !USE_WEAK_SEEDING */
}


int
rand_r(unsigned int *ctx)
{
        u_long val;
        int r;

#ifdef  USE_WEAK_SEEDING
        val = *ctx;
#else
        /* Transform to [1, 0x7ffffffe] range. */
        val = (*ctx % 0x7ffffffe) + 1;
#endif
        r = do_rand(&val);

#ifdef  USE_WEAK_SEEDING
        *ctx = (unsigned int)val;
#else
        *ctx = (unsigned int)(val - 1);
#endif
        return (r);
}


static u_long next =
#ifdef  USE_WEAK_SEEDING
    1;
#else
    2;
#endif

int
rand(void)
{
        return (do_rand(&next));
}

void
srand(u_int seed)
{
        next = seed;
#ifndef USE_WEAK_SEEDING
        /* Transform to [1, 0x7ffffffe] range. */
        next = (next % 0x7ffffffe) + 1;
#endif
}


/*
 * sranddev:
 *
 * Many programs choose the seed value in a totally predictable manner.
 * This often causes problems.  We seed the generator using pseudo-random
 * data from the kernel.
 */
void
sranddev(void)
{
        int mib[2];
        size_t len;

        len = sizeof(next);

        mib[0] = CTL_KERN;
        mib[1] = KERN_ARND;
        sysctl(mib, 2, (void *)&next, &len, NULL, 0);
#ifndef USE_WEAK_SEEDING
        /* Transform to [1, 0x7ffffffe] range. */
        next = (next % 0x7ffffffe) + 1;
#endif
}


#ifdef TEST

main()
{
    int i;
    unsigned myseed;

    printf("seeding rand with 0x19610910: \n");
    srand(0x19610910);

    printf("generating three pseudo-random numbers:\n");
    for (i = 0; i < 3; i++)
    {
        printf("next random number = %d\n", rand());
    }

    printf("generating the same sequence with rand_r:\n");
    myseed = 0x19610910;
    for (i = 0; i < 3; i++)
    {
        printf("next random number = %d\n", rand_r(&myseed));
    }

    return 0;
}

#endif /* TEST */

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
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
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
114	rand(void)
115	{
116	return (do_rand(&next));
117	}
118
119	void
120	srand(u_int seed)
121	{
122	next = seed;
123	#ifndef USE_WEAK_SEEDING
124	/* Transform to [1, 0x7ffffffe] range. */
125	next = (next % 0x7ffffffe) + 1;
126	#endif
127	}
128
129
130	/*
131	* sranddev:
132	*
133	* Many programs choose the seed value in a totally predictable manner.
134	* This often causes problems. We seed the generator using pseudo-random
135	* data from the kernel.
136	*/
137	void
138	sranddev(void)
139	{
140	int mib[2];
141	size_t len;
142
143	len = sizeof(next);
144
145	mib[0] = CTL_KERN;
146	mib[1] = KERN_ARND;
147	sysctl(mib, 2, (void *)&next, &len, NULL, 0);
148	#ifndef USE_WEAK_SEEDING
149	/* Transform to [1, 0x7ffffffe] range. */
150	next = (next % 0x7ffffffe) + 1;
151	#endif
152	}
153
154
155	#ifdef TEST
156
157	main()
158	{
159	int i;
160	unsigned myseed;
161
162	printf("seeding rand with 0x19610910: \n");
163	srand(0x19610910);
164
165	printf("generating three pseudo-random numbers:\n");
166	for (i = 0; i < 3; i++)
167	{
168	printf("next random number = %d\n", rand());
169	}
170
171	printf("generating the same sequence with rand_r:\n");
172	myseed = 0x19610910;
173	for (i = 0; i < 3; i++)
174	{
175	printf("next random number = %d\n", rand_r(&myseed));
176	}
177
178	return 0;
179	}
180
181	#endif /* TEST */
182