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Diffstat (limited to 'lib/libc/stdlib/rand.c')
| -rw-r--r-- | lib/libc/stdlib/rand.c | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c new file mode 100644 index 0000000..0cbd948 --- /dev/null +++ b/lib/libc/stdlib/rand.c @@ -0,0 +1,158 @@ +/*- + * 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. + * 4. 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; + + /* Can't be initialized with 0, so use another value. */ + if (*ctx == 0) + *ctx = 123459876; + hi = *ctx / 127773; + lo = *ctx % 127773; + x = 16807 * lo - 2836 * hi; + if (x < 0) + x += 0x7fffffff; + return ((*ctx = x) % ((u_long)RAND_MAX + 1)); +#endif /* !USE_WEAK_SEEDING */ +} + + +int +rand_r(unsigned int *ctx) +{ + u_long val = (u_long) *ctx; + int r = do_rand(&val); + + *ctx = (unsigned int) val; + return (r); +} + + +static u_long next = 1; + +int +rand() +{ + return (do_rand(&next)); +} + +void +srand(seed) +u_int seed; +{ + next = seed; +} + + +/* + * 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); +} + + +#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 */ + |
