//******************************************************************************
//
// File:    PiSmp2.java
// Package: edu.rit.smp.monte
// Unit:    Class edu.rit.smp.monte.PiSmp2
//
// This Java source file is copyright (C) 2008 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ 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 General Public License for more details.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************

package edu.rit.smp.monte;

//import edu.rit.pj.Comm;
import edu.rit.pj.LongForLoop;
import edu.rit.pj.ParallelTeam;
import edu.rit.pj.ParallelRegion;

import edu.rit.pj.reduction.SharedLong;

import java.util.Random;

/**
 * Class PiSmp2 is an SMP parallel program that calculates an approximate value
 * for π using a Monte Carlo technique. The program generates a number of
 * random points in the unit square (0,0) to (1,1) and counts how many of them
 * lie within a circle of radius 1 centered at the origin. The fraction of the
 * points within the circle is approximately π/4.
 * <P>
 * Usage: java -Dpj.nt=<I>K</I> edu.rit.smp.monte.PiSmp2 <I>seed</I> <I>N</I>
 * <BR><I>K</I> = Number of parallel threads
 * <BR><I>seed</I> = Random seed
 * <BR><I>N</I> = Number of random points
 * <P>
 * The computation is performed in parallel in multiple threads. To improve
 * performance, each thread has its own pseudorandom number generator, and the
 * program uses the reduction pattern to determine the count. The program
 * measures the computation's running time.
 *
 * @author  Alan Kaminsky
 * @version 29-Feb-2008
 */
public class PiSmp2
    {

// Prevent construction.

    private PiSmp2()
        {
        }

// Program shared variables.

    // Command line arguments.
    static long seed;
    static long N;

    // Number of points within the unit circle.
    static SharedLong count;

// Main program.

    /**
     * Main program.
     */
    public static void main
        (String[] args)
        throws Exception
        {
        //Comm.init (args);

        // Start timing.
        long time = -System.currentTimeMillis();

        // Validate command line arguments.
        if (args.length != 2) usage();
        seed = Long.parseLong (args[0]);
        N = Long.parseLong (args[1]);

        // Generate n random points in the unit square, count how many are in
        // the unit circle.
        count = new SharedLong (0);
        new ParallelTeam().execute (new ParallelRegion()
            {
            public void run() throws Exception
                {
                execute (0, N-1, new LongForLoop()
                    {
                    // Set up per-thread PRNG and counter.
                    Random prng_thread = new Random (seed);
                    long count_thread = 0;

                    // Extra padding to avert cache interference.
                    long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
                    long pad8, pad9, pada, padb, padc, padd, pade, padf;

                    // Parallel loop body.
                    public void run (long first, long last)
                        {
                        // Generate random points.
                        for (long i = first; i <= last; ++ i)
                            {
                            double x = prng_thread.nextDouble();
                            double y = prng_thread.nextDouble();
                            if (x*x + y*y <= 1.0) ++ count_thread;
                            }
                        }

                    public void finish()
                        {
                        // Reduce per-thread counts into shared count.
                        count.addAndGet (count_thread);
                        }
                    });
                }
            });

        // Stop timing.
        time += System.currentTimeMillis();

        // Print results.
        System.out.println
            ("pi = 4 * " + count + " / " + N + " = " +
             (4.0 * count.doubleValue() / N));
        System.out.println (time + " msec");
        }

// Hidden operations.

    /**
     * Print a usage message and exit.
     */
    private static void usage()
        {
        System.err.println ("Usage: java -Dpj.nt=<K> edu.rit.smp.monte.PiSmp2 <seed> <N>");
        System.err.println ("<K> = Number of parallel threads");
        System.err.println ("<seed> = Random seed");
        System.err.println ("<N> = Number of random points");
        System.exit (1);
        }

    }