// Copyright (C) 2001-2003
// William E. Kempf
//
//  Distributed under the Boost Software License, Version 1.0. (See accompanying 
//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#include 
#include 

class factorial
{
public:
    factorial(int x, int& res) : x(x), res(res) { }
    void operator()() { res = calculate(x); }
    int result() const { return res; }

private:
    int calculate(int x) { return x