package corejava;

/**
    An improved random number generator based on Algorithm B
    in Knuth Vol 2 p32.
    Gives a set of random integers that does not exhibit
    as much correlation as the method used by the Java random number generator.

    @version 1.01 15 Feb 1996
    @author Cay Horstmann
*/

public class RandomIntGenerator
{  /**
       Constructs an object that generates random integers in a given range
       @param l the lowest integer in the range
       @param h the highest integer in the range
    */

    public RandomIntGenerator(int l, int h)
    {  low = l;
       high = h;
    }

    /**
       Generates a random integer in a range of integers
       @return a random integer
    */

    public int draw()
    {  int r = low
          + (int)((high - low + 1) * nextRandom());
       return r;
    }

    /**
       test stub for the class
    */

    public static void main(String[] args)
    {  RandomIntGenerator r1
          = new RandomIntGenerator(1, 10);
       RandomIntGenerator r2
          = new RandomIntGenerator(0, 1);
       int i;
       for (i = 1; i <= 100; i++)
          System.out.println(r1.draw() + " " + r2.draw());
    }

    private static double nextRandom()
    {  int pos =
          (int)(java.lang.Math.random() * BUFFER_SIZE);
       if (pos == BUFFER_SIZE) pos = BUFFER_SIZE - 1;
       double r = buffer[pos];
       buffer[pos] = java.lang.Math.random();
       return r;
    }

    private static final int BUFFER_SIZE = 101;
    private static double[] buffer
       = new double[BUFFER_SIZE];
    static
    {  int i;
       for (i = 0; i < BUFFER_SIZE; i++)
          buffer[i] = java.lang.Math.random();
    }

    private int low;
    private int high;
}