//  Factorial.two.cpp

//  Use the simple (add only, non-negative) BigInt 
//  class to calculate very large factorials.

//  tom bailey  17 feb 00

//  Version two uses a faster multiply by adding
//  algorithm to speed up the calculation.

//  tom bailey  18 feb 00

#include <iostream>
using namespace std;

#include "BigInt.h"
#include "timer.h"


int
main() {
	short n;

	cout << "Enter n for n!: ";
	cin >> n;

	while( n >= 0 ) {
		Timer watch;
		watch.start();

		BigInt fact( 1 );
		for( short i=1; i<=n; i++ ) {
			BigInt sum( 0 );
			BigInt factor( fact );
			short mult = i;
			while( mult > 0 ) {
				if( mult%2 == 1 ) {
					sum += factor;
					mult--;
				}
				else {
					factor += factor;
					mult /= 2;
				}
			}
			fact = sum;
		}

		watch.stop();

		cout << "factorial( " << n << " ) = " << fact;
		cout << endl;
		cout << "  time required = " << watch.time();
		cout << endl << endl;

		cout << "Enter n for n!: ";
		cin >> n;
	}

	return 0;
}