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Diffstat (limited to 'lib/libc/stdlib/rand.c')
| -rw-r--r-- | lib/libc/stdlib/rand.c | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c new file mode 100644 index 000000000000..31b51b327a0d --- /dev/null +++ b/lib/libc/stdlib/rand.c @@ -0,0 +1,162 @@ +/*- + * SPDX-License-Identifier: BSD-3-Clause + * + * 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>. + */ + +#include "namespace.h" +#include <sys/param.h> +#include <sys/sysctl.h> +#include <assert.h> +#include <pthread.h> +#include <stdbool.h> +#include <stdlib.h> +#include <syslog.h> +#include "un-namespace.h" + +#include "libc_private.h" +#include "random.h" + +/* + * Implement rand(3), the standard C PRNG API, using the non-standard but + * higher quality random(3) implementation and the same size 128-byte state + * LFSR as the random(3) default. + * + * It turns out there are portable applications that want a PRNG but are too + * lazy to use better-but-nonstandard interfaces like random(3), when + * available, and too lazy to import higher-quality and faster PRNGs into their + * codebase (such as any of SFC, JSF, 128-bit LCGs, PCG, or Splitmix64). + * + * Since we're stuck with rand(3) due to the C standard, we can at least have + * it produce a relatively good PRNG sequence using our existing random(3) + * LFSR. The random(3) design is not particularly fast nor compact, but it has + * the advantage of being the one already in the tree. + */ +static struct __random_state *rand3_state; +static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT; + +static void +initialize_rand3(void) +{ + int error; + + rand3_state = allocatestate(TYPE_3); + error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3); + assert(error == 0); +} + +int +rand(void) +{ + _once(&rand3_state_once, initialize_rand3); + return ((int)random_r(rand3_state)); +} + +void +srand(unsigned seed) +{ + _once(&rand3_state_once, initialize_rand3); + srandom_r(rand3_state, seed); +} + +/* + * FreeBSD 12 and prior compatibility implementation of rand(3). + */ +static int +do_rand(unsigned long *ctx) +{ +/* + * 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; + + /* Transform to [1, 0x7ffffffe] range. */ + x = (*ctx % 0x7ffffffe) + 1; + hi = x / 127773; + lo = x % 127773; + x = 16807 * lo - 2836 * hi; + if (x < 0) + x += 0x7fffffff; + /* Transform to [0, 0x7ffffffd] range. */ + x--; + *ctx = x; + return (x); +} + +/* + * Can't fix this garbage; too little state. + */ +int +rand_r(unsigned *ctx) +{ + u_long val; + int r; + + val = *ctx; + r = do_rand(&val); + *ctx = (unsigned)val; + return (r); +} + +static u_long next = 1; + +int __rand_fbsd12(void); +int +__rand_fbsd12(void) +{ + return (do_rand(&next)); +} +__sym_compat(rand, __rand_fbsd12, FBSD_1.0); + +void __srand_fbsd12(unsigned seed); +void +__srand_fbsd12(unsigned seed) +{ + next = seed; +} +__sym_compat(srand, __srand_fbsd12, FBSD_1.0); + +void __sranddev_fbsd12(void); +void +__sranddev_fbsd12(void) +{ + static bool warned = false; + + if (!warned) { + syslog(LOG_DEBUG, "Deprecated function sranddev() called"); + warned = true; + } +} +__sym_compat(sranddev, __sranddev_fbsd12, FBSD_1.0); |