freebsd-dev/lib/libc/stdlib/rand.c

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/*-
* 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
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* 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.
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*
* Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
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*/
#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("$FreeBSD$");
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#include "namespace.h"
#include <sys/param.h>
#include <sys/sysctl.h>
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#include <sys/types.h>
#include <stdlib.h>
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#include "un-namespace.h"
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#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.
*/
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return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
#else /* !USE_WEAK_SEEDING */
/*
* Compute x = (7^5 * x) mod (2^31 - 1)
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* 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 */
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}
int
rand_r(unsigned int *ctx)
{
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u_long val;
int r;
#ifdef USE_WEAK_SEEDING
val = *ctx;
#else
/* Transform to [1, 0x7ffffffe] range. */
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val = (*ctx % 0x7ffffffe) + 1;
#endif
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r = do_rand(&val);
#ifdef USE_WEAK_SEEDING
*ctx = (unsigned int)val;
#else
*ctx = (unsigned int)(val - 1);
#endif
return (r);
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}
static u_long next =
#ifdef USE_WEAK_SEEDING
1;
#else
2;
#endif
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int
rand()
{
return (do_rand(&next));
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}
void
srand(seed)
u_int seed;
{
next = seed;
#ifndef USE_WEAK_SEEDING
/* Transform to [1, 0x7ffffffe] range. */
next = (next % 0x7ffffffe) + 1;
#endif
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}
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/*
* 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()
{
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
}
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#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 */