/*- * 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 >.

 * Источник: http://sources.freebsd.org/RELENG_8/src/lib/libc/stdlib/rand.c

 */

#if defined(LIBC_SCCS) && !defined(lint)

 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93";

#endif

/* LIBC_SCCS и не lint */

#include < sys/cdefs.h >
__FBSDID("$FreeBSD$");

#include "namespace.h"

#include < sys/time.h >          /* Для sranddev() */

#include < sys/types.h >

#include < fcntl.h >             /* Для sranddev() */

#include < stdlib.h >

#include < unistd.h >            /* Для sranddev() */

#include "un-namespace.h"

#ifdef TEST

 #include < stdio.h >

#endif /* Тест */

static int do_rand (unsigned long *ctx)
{

#ifdef  USE_WEAK_SEEDING

/*

 * Реализация для исторической совместимости.

 * Случайные последовательности не очень меняются

 * в зависимости от seed, даже с переполнением.

 */
   return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));

#else   /* !USE_WEAK_SEEDING */

/*

 * Вычисляет x = (7^5 * x) mod (2^31 - 1)

 * с переполнением по 31 битам:

 *      (2^31 - 1) = 127773 * (7^5) + 2836

 * Из публикации "Генераторы случайных чисел: хорошие найти трудно"

 * ("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;
   /* Нельзя инициализировать нулем, поэтому будем использовать

      другое значение. */
   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 (void)
{
   return (do_rand(&next));
}

void srand(u_int seed)
{
   next = seed;
}

/*

 * sranddev:

 *

 * Многие программы выбирают значение seed легко предсказуемым способом.

 * Это часто приводит к проблемам. Мы настраиваем seed с помощью намного

 * более безопасного интерфейса random(4).

 */

void sranddev(void)
{
   int fd, done;
   done = 0;
   fd = _open("/dev/random", O_RDONLY | O_CLOEXEC, 0);
   if (fd >= 0)
   {
      if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
         done = 1;
      _close(fd);
   }
   if (!done)
   {
      struct timeval tv;
      gettimeofday(&tv, NULL);
      srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec);
   }
}

#ifdef TEST

int main (void)
{
   int i;
   unsigned myseed;

   printf("Предустанавливаем rand числом 0x19610910: \n");
   srand(0x19610910);
   printf("генерируем 3 псевдослучайных числа:\n");
   for (i = 0; i < 3; i++)
   {
      printf("очередное случайное число = %d\n", rand());
   }

   printf("генерируем точно такую же последовательность, используя rand_r:\n");
   myseed = 0x19610910;

   for (i = 0; i < 3; i++)
   {
      printf("очередное случайное число = %d\n", rand_r(&myseed));
   }
   return 0;
}

#endif /* TEST */