StdLib/LibC/StdLib/Rand.c

/*-
 * Portions Copyright (c) 2010, Intel Corporation. All rights reserved.<BR>
 * Copyright (c) 1990, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
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 *    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
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 * 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
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 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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//__FBSDID("$FreeBSD: src/lib/libc/stdlib/rand.c,v 1.17.2.1.2.1 2009/10/25 01:10:29 kensmith Exp $");
#include  <LibConfig.h>

#include  <stdlib.h>

static UINT32 next = 1;

/** Compute a pseudo-random number.
  *
  * 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.
**/
int
rand()
{
  INT32 hi, lo, x;

  /* Can't be initialized with 0, so use another value. */
  if (next == 0)
    next = 123459876;
  hi = next / 127773;
  lo = next % 127773;
  x = 16807 * lo - 2836 * hi;
  if (x < 0)
    x += 0x7fffffff;
  return ((next = x) % ((UINT32)RAND_MAX + 1));
}

void
srand(unsigned int seed)
{
  next = (UINT32)seed;
}