/* Minimal Standard Random Number Generator, from "Random Number Generators: */
/* Good Ones Are Hard To Find", Communications of the ACM, October 1988,     */
/* Volume 31 Number 10.                                                      */

// Copyright (C)2013-2018, Philip Munts, President, Munts AM Corp.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
//   this list of conditions and the following disclaimer.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT HOLDER 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.

#include <stdlib.h>

#define A	16807
#define M	2147483647
#define Q	127773
#define R	2836

static unsigned int seed = 1;

int rand_r(unsigned int *s)
{
  int hi, lo, test;

  hi = *s / Q;
  lo = *s % Q;
  test = A*lo - R*hi;

  if (test > 0)
    *s = test;
  else
    *s = test + M;

  return *s/M;
}

int rand(void)
{
  return rand_r(&seed);
}

void srand(unsigned int s)
{
  seed = s;
}