//  Boost pow.hpp header file
//  Computes a power with exponent known at compile-time

//  (C) Copyright Bruno Lalande 2008.
//  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)

// See http://www.boost.org for updates, documentation, and revision history.


#ifndef BOOST_MATH_POW_HPP
#define BOOST_MATH_POW_HPP


#include <boost/mpl/greater_equal.hpp>


namespace boost {
namespace math {


namespace detail {


template <int N>
struct positive_power;

template <>
struct positive_power<2>
{
    template <typename T>
    static double result(T base)
    { return base*base; }
};

template <>
struct positive_power<0>
{
    template <typename T>
    static double result(T)
    { return 1; }
};

template <int N>
struct positive_power
{
    template <typename T>
    static double result(T base)
    {
        return (N%2) ? base*positive_power<N-1>::result(base)
                     : positive_power<2>::result(
                           positive_power<N/2>::result(base)
                       );
    }
};


template <int N, bool>
struct power_if_positive
{
    template <typename T>
    static double result(T base)
    { return positive_power<N>::result(base); }
};

template <int N>
struct power_if_positive<N, false>
{
    template <typename T>
    static double result(T base)
    { return 1/positive_power<-N>::result(base); }
};


}  // namespace detail


template <int N, typename T>
double pow(T base)
{
    typedef typename mpl::greater_equal<
                         mpl::int_<N>,
                         mpl::int_<0>
                     >::type is_positive;

    return detail::power_if_positive<N, is_positive::value>::result(base);
}


}  // namespace math
}  // namespace boost


#endif