import java.util.Random;

/**
 * We have broken up the computation of the average into computation
 * of chunks of the intial sum.  Here, they happen one at a time,
 * but in the final version they will happen in parallel.
 */
public class ArrayAverageChunk {

    /**
     * Chunked unit of work for computing the sum.
     */
    private static double sum(int start, int end, Double arr[]) {
        double tmp = 0;
        for (int i = start; i<end; i++) {
            tmp += arr[i];
        }
        return tmp;
    }

    private static int num = 2500000;
    private static int units = 10;
    private static Double arr[];
    
    /**
     * Single-threaded, chunked computation
     */
    private static void computeSTchunk() {
        long start = System.currentTimeMillis();
        double tmp = 0;
        for (int i = 0; i<units; i++) {
            int startIdx = i*(num/units);
            int endIdx = (i == units-1) ? num : (i+1)*(num/units);
            tmp += sum(startIdx,endIdx,arr);
        }
        tmp = tmp / (double)num;
        long end = System.currentTimeMillis();
        System.out.println("Result (ST, "+(end-start)+" ms) = "+tmp);
    }

    /**
     * Single-threaded computation
     */
    private static void computeST() {
        long start = System.currentTimeMillis();
        double tmp = 0;
        for (int i = 0; i<num; i++) {
            tmp += arr[i];
        }
        tmp = tmp / (double)num;
        long end = System.currentTimeMillis();
        System.out.println("Result (ST, "+(end-start)+" ms) = "+tmp);
    }
    
    /** 
     * Creates an array of the given size with random contents.
     */
    static private Random rand = new Random();
    public static Double[] createRand(int num) {
        Double[] result = new Double[num];
        for(int i = 0 ; i < num; i++)
            result[i] = rand.nextDouble();
        return result;
    }

    public static void main(String args[]) {
        boolean doSingle = true;
        boolean doMT = true;
        boolean doMTComp = true;
        if (args.length >= 1)
            num = new Integer(args[0]);
        if (args.length >= 2)
            units = new Integer(args[1]);
        System.out.println("array size = "+num);
        System.out.println("units = "+units);
        System.out.println("Constructing input array ...");
        System.out.flush();

        arr = createRand(num);

        System.out.println("Starting runs ...");
        System.out.flush();
        computeST();
        computeSTchunk();
    }    
}