cvd/random.h

/*                       
    This file is part of the CVD Library.

    Copyright (C) 2005 The Authors

    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 2.1 of the License, 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., 
    51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/
#ifndef CVD_RANDOM_H
#define CVD_RANDOM_H

#include <cstdlib>
#include <cmath>

namespace CVD {
    inline double rand_u()
    {
        return ((double) std::rand()/ RAND_MAX);
    }

    inline double rand_g()
    {
        static bool use_old=false;
        static double y2;
        double r;


        if(!use_old)
        {
            double x1, x2, w, y1;
            do {
                x1 = 2.0 * rand_u() - 1.0;
                x2 = 2.0 * rand_u() - 1.0;
                w = x1 * x1 + x2 * x2;
            } while ( w >= 1.0 );

            w = std::sqrt( (-2.0 * std::log( w ) ) / w );
            y1 = x1 * w;
            y2 = x2 * w;

            r = y1;
            use_old = true;
        }
        else
        {
            r = y2;
            use_old = false;
        }


        return r;
    }

}

#endif

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