7774e759a0
reading hard. 2) Instead of doing range transformation in each and every function here, do it single time directly in do_rand(). One "mod" operation overhead is not a big deal, but the code looks nicer and possible future functions additions or PRNG change do not miss range transformations neither have unneeded ones. 3) Use POSIX argument types for visible functions (cosmetic). MFC after: 1 week
152 lines
3.6 KiB
C
152 lines
3.6 KiB
C
/*-
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 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
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93";
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#endif /* LIBC_SCCS and not lint */
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "namespace.h"
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#include <sys/param.h>
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#include <sys/sysctl.h>
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#include <stdlib.h>
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#include "un-namespace.h"
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#ifdef TEST
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#include <stdio.h>
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#endif /* TEST */
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static int
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do_rand(unsigned long *ctx)
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{
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/*
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* Compute x = (7^5 * x) mod (2^31 - 1)
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* without overflowing 31 bits:
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* (2^31 - 1) = 127773 * (7^5) + 2836
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* From "Random number generators: good ones are hard to find",
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* Park and Miller, Communications of the ACM, vol. 31, no. 10,
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* October 1988, p. 1195.
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*/
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long hi, lo, x;
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/* Transform to [1, 0x7ffffffe] range. */
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x = (*ctx % 0x7ffffffe) + 1;
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hi = x / 127773;
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lo = x % 127773;
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x = 16807 * lo - 2836 * hi;
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if (x < 0)
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x += 0x7fffffff;
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/* Transform to [0, 0x7ffffffd] range. */
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x--;
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*ctx = x;
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return (x);
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}
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int
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rand_r(unsigned *ctx)
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{
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u_long val;
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int r;
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val = *ctx;
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r = do_rand(&val);
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*ctx = (unsigned)val;
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return (r);
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}
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static u_long next = 1;
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int
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rand(void)
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{
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return (do_rand(&next));
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}
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void
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srand(unsigned seed)
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{
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next = seed;
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}
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/*
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* sranddev:
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*
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* Many programs choose the seed value in a totally predictable manner.
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* This often causes problems. We seed the generator using pseudo-random
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* data from the kernel.
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*/
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void
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sranddev(void)
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{
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int mib[2];
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size_t len;
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len = sizeof(next);
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mib[0] = CTL_KERN;
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mib[1] = KERN_ARND;
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sysctl(mib, 2, (void *)&next, &len, NULL, 0);
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}
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#ifdef TEST
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main()
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{
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int i;
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unsigned myseed;
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printf("seeding rand with 0x19610910: \n");
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srand(0x19610910);
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printf("generating three pseudo-random numbers:\n");
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for (i = 0; i < 3; i++)
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{
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printf("next random number = %d\n", rand());
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}
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printf("generating the same sequence with rand_r:\n");
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myseed = 0x19610910;
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for (i = 0; i < 3; i++)
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{
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printf("next random number = %d\n", rand_r(&myseed));
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}
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return 0;
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}
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#endif /* TEST */
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