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;
}