1:  package de.luschny.math.factorial;

   2:   

   3:  import de.luschny.math.arithmetic.Xint;

   4:   

   5:  public class FactorialProductRecursive implements IFactorialFunction

   6:  {

   7:   

   8:      public FactorialProductRecursive()

   9:      {

  10:      }

  11:   

  12:      public String getName()

  13:      {

  14:          return "ProductRecursive  ";

  15:      }

  16:   

  17:      public Xint factorial(int n)

  18:      {

  19:          if (n < 0)

  20:          {

  21:              throw new ArithmeticException("Factorial: n has to be >= 0, but was " + n);

  22:          }

  23:   

  24:          if (1 < n)

  25:          {

  26:              return recProduct(1, n);

  27:          }

  28:   

  29:          return Xint.ONE;

  30:      }

  31:   

  32:      private Xint recProduct(int n, int len)

  33:      {

  34:          if (1 < len)

  35:          {

  36:              int l = len / 2;

  37:              return recProduct(n, l).multiply(recProduct(n + l, len - l));

  38:          }

  39:   

  40:          return Xint.valueOf(n);

  41:      }

  42:  } // endOfFactorialProductRecursive