Randomizer.h

// Randomizer.h -- Interface for a random number generator.

/*
 * Copyright (C) 1997, 1998, 2004 Tudor Hulubei <tudor@hulubei.net>.
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2, or (at
 * your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA,
 * 02111-1307, USA.
 */

/*
 * NOTE: This is an interal header file.
 * You should not attempt to use it directly.
 */

// $Id: Randomizer_8h-source.html,v 1.1 2005/05/25 12:37:18 tudor Exp $

#ifndef _CSP_KERNEL_Randomizer_H
#define _CSP_KERNEL_Randomizer_H


#include <cstdlib>
#include <cmath>


CSP_NAMESPACE_BEGIN(csp);


/*
 * In Numerical Recipes in C: The Art of Scientific Computing (William H.
 * Press, Brian  P. Flannery, Saul  A. Teukolsky, William T.  Vetterling;
 * New York:  Cambridge  University Press, 1990  (1st ed,   p. 207)), the
 * following comments are made:
 *
 * "If you want to generate a random integer between 1 and 10, you should
 * always do it by:
 *
 *      j = 1 + (int)(10.0 * rand() / (RAND_MAX + 1.0));
 *
 *      and never by anything resembling
 *
 *      j = 1 + ((int)(1000000.0 * rand()) % 10);
 *
 *      (which uses lower-order bits)."
 *
 * ... which is what we do when we use the system's pseudo-random
 * number generator.  However, to make it easier for other researchers
 * to reproduce our results (as well as for us to reproduce theirs),
 * and to make sure that given a set of parameters the same problem is
 * generated on different platforms, the default is to use William
 * H. Press, et al.'s random number generator from "Numerical Recipes
 * in C", Second Edition with corrections (1994) page 282.
 */

class CSP_API Randomizer
{
  public:
    Randomizer(bool systemPRNG = false) :
        m_systemPRNG(systemPRNG) {}

    void setSeed(unsigned int seed)
    {
        if (m_systemPRNG)
            srand(seed);
        else
            m_seed = -abs(static_cast<int>(seed));
    }

    int next(int limit)
    {
        if (m_systemPRNG)
            return int(double(limit) * rand() / (RAND_MAX + 1.0));
        else
            return static_cast<int>(ran2(&m_seed) * limit);
    }

  private:
    float ran2(long* idum);

    bool m_systemPRNG;

    long m_seed;
};


CSP_NAMESPACE_END(csp);


#endif // _CSP_KERNEL_Randomizer_H

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