vpUniRand.cpp

/****************************************************************************
 *
 * This file is part of the ViSP software.
 * Copyright (C) 2005 - 2017 by Inria. All rights reserved.
 *
 * This software is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * ("GPL") version 2 as published by the Free Software Foundation.
 * See the file LICENSE.txt at the root directory of this source
 * distribution for additional information about the GNU GPL.
 *
 * For using ViSP with software that can not be combined with the GNU
 * GPL, please contact Inria about acquiring a ViSP Professional
 * Edition License.
 *
 * See http://visp.inria.fr for more information.
 *
 * This software was developed at:
 * Inria Rennes - Bretagne Atlantique
 * Campus Universitaire de Beaulieu
 * 35042 Rennes Cedex
 * France
 *
 * If you have questions regarding the use of this file, please contact
 * Inria at visp@inria.fr
 *
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Description:
 * Generation of random number with uniform and normal probability density.
 *
 * Authors:
 * Eric Marchand
 *
 *****************************************************************************/

#include <math.h>
#include <visp3/core/vpUniRand.h>

inline void
vpUniRand::draw0()
{
  long k= x/q;//temp value for computing without overflow
  x = a*(x-k*q)-k*r;
  if (x < 0) x += m; //compute x without overflow
}

double
vpUniRand::draw1()
{
  const long ntab = 33;  //we work on a 32 elements array.
                                  //the 33rd one is actually the first value of y.
  const long modulo = ntab-2;

  static long y = 0;
  static long T[ntab];

  long j; //index of T

  //step 0
  if (!y) { //first time
    for(j = 0; j < ntab; j++) {
      draw0();
      T[j]=x;
    } //compute table T
    y=T[ntab-1];
  }

  //step 1
  j = y & modulo; //compute modulo ntab+1 (the first element is the 0th)

  //step 3
  y=T[j];
  double ans = (double)y/normalizer;

  //step 4
  //generate x(k+i) and set y=x(k+i)
  draw0();

  //refresh T[j];
  T[j]=x;

  return ans;
}