package umontreal.iro.lecuyer.hups;
/* *
 * Title:        

 * Description:  

 * Copyright:    Copyright (c) 

 * Company:      

 * @author
 * @version 1.0
 */
import umontreal.iro.lecuyer.util.PrintfFormat;
import cern.colt.list.*;


/**
 * Implements a recurrence-based point set defined via a linear 
 * congruential recurrence of the form 
 * xi = axi-1mod n
 * and 
 * ui = xi/n.  The implementation is done by storing the values
 * of ui over the set of all cycles of the recurrence.
 * 
 */
public class LCGPointSet extends CycleBasedPointSet  {

      private int a;                      // Multiplier.




   /**
    * Constructs and stores the set of cycles for an LCG with
    *    modulus n and multiplier a.
    *   If the LCG has full period length n - 1,
    * there are two cycles, the first one containing only 0 
    *   and the second one of period length n - 1.
    *  
    * @param n required number of points and modulus of the LCG
    * 
    *    @param a generator a of the LCG
    * 
    * 
    */
   public LCGPointSet (int n, int a)  {
      this.a = a;
      double invn = 1.0 / (double)n;   // 1/n
      DoubleArrayList c;  // Array used to store the current cycle.
      long currentState;  // The state currently visited. 
      int i;
      boolean stateVisited[] = new boolean[n];  
         // Indicates which states have been visited so far.
      for (i = 0; i < n; i++)
         stateVisited[i] = false;
      int startState = 0;    // First state of the cycle currently considered.
      numPoints = 0;
      while (startState < n) {
         stateVisited[startState] = true;
         c = new DoubleArrayList();
         c.add (startState * invn);
         // We use the fact that a "long" has 64 bits in Java.
         currentState = (startState * (long)a) % (long)n;
         while (currentState != startState) {
            stateVisited[(int)currentState] = true;
            c.add (currentState * invn);
            currentState = (currentState * (long)a) % (long)n;
            }
         addCycle (c);
         for (i = startState+1; i < n; i++)
            if (stateVisited[i] == false)
                break;
         startState = i;
         }
      }


   /**
    * Constructs and stores the set of cycles for an LCG with
    *    modulus 
    * n = be + c and multiplier a.
    * 
    */
   public LCGPointSet (int b, int e, int c, int a)  {
      this (computeModulus (b, e, c), a);
   }

   private static int computeModulus (int b, int e, int c) {
      int n;
      int i;
      if (b == 2) 
         n = (1 << e);
      else {
         for (i = 1, n = b;  i < e;  i++)  n *= b;
         }
      n += c;
      return n;
   }


   public String toString() {
      StringBuffer sb = new StringBuffer ("LCGPointSet:" +
                                           PrintfFormat.NEWLINE);
      sb.append (super.toString());
      sb.append (PrintfFormat.NEWLINE + "Multiplier a: ");
      sb.append (a);
      return sb.toString();
   }


   /**
    * Returns the value of the multiplier a.
    * 
    */
   public int geta ()  {
      return a;
   }
}