conversion_impl.hpp

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// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
// unit/quantity manipulation and conversion
//
// Copyright (C) 2003-2008 Matthias Christian Schabel
// Copyright (C) 2007-2008 Steven Watanabe
//
// 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)

#ifndef BOOST_UNITS_DETAIL_CONVERSION_IMPL_HPP
#define BOOST_UNITS_DETAIL_CONVERSION_IMPL_HPP

#include <boost/mpl/bool.hpp>
#include <boost/mpl/and.hpp>
#include <boost/mpl/divides.hpp>
#include <boost/preprocessor/seq/enum.hpp>
#include <boost/type_traits/is_same.hpp>

#include <boost/units/heterogeneous_system.hpp>
#include <boost/units/homogeneous_system.hpp>
#include <boost/units/reduce_unit.hpp>
#include <boost/units/static_rational.hpp>
#include <boost/units/units_fwd.hpp>
#include <boost/units/detail/dimension_list.hpp>
#include <boost/units/detail/heterogeneous_conversion.hpp>
#include <boost/units/detail/one.hpp>
#include <boost/units/detail/static_rational_power.hpp>
#include <boost/units/detail/unscale.hpp>

#include <boost/units/units_fwd.hpp>

namespace boost {

namespace units {

namespace detail {

template<class Source, class Dest>
struct conversion_factor_helper;

template<class Source, class Dest>
struct call_base_unit_converter;

}

/// INTERNAL ONLY
struct undefined_base_unit_converter_base {
    static const bool is_defined = false;
};

/// INTERNAL ONLY
struct no_default_conversion {
    static const bool is_defined = false;
};

/// INTERNAL ONLY
template<class BaseUnit>
struct unscaled_get_default_conversion : no_default_conversion { };

/// INTERNAL ONLY
template<bool is_defined>
struct unscaled_get_default_conversion_impl;

/// INTERNAL ONLY
template<>
struct unscaled_get_default_conversion_impl<true>
{
    template<class T>
    struct apply
    {
        typedef typename unscaled_get_default_conversion<typename unscale<T>::type>::type type;
    };
};

/// INTERNAL ONLY
template<>
struct unscaled_get_default_conversion_impl<false>
{
    template<class T>
    struct apply
    {
        typedef typename T::unit_type type;
    };
};

/// INTERNAL ONLY
template<class BaseUnit>
struct get_default_conversion
{
    typedef typename unscaled_get_default_conversion_impl<
        unscaled_get_default_conversion<typename unscale<BaseUnit>::type>::is_defined
    >::template apply<BaseUnit>::type type;
};

/// INTERNAL ONLY
template<class Source, class Destination>
struct select_base_unit_converter
{
    typedef Source source_type;
    typedef Destination destination_type;
};

/// INTERNAL ONLY
template<class Source, class Dest>
struct base_unit_converter_base : undefined_base_unit_converter_base {
};

/// INTERNAL ONLY
template<class Source>
struct base_unit_converter_base<Source, BOOST_UNITS_MAKE_HETEROGENEOUS_UNIT(Source, typename Source::dimension_type)>
{
    static const bool is_defined = true;
    typedef one type;
    static type value() {
        return(one());
    }
};

/// INTERNAL ONLY
template<class Source, class Dest>
struct base_unit_converter : base_unit_converter_base<Source, Dest> { };

namespace detail {

template<class Source, class Dest>
struct do_call_base_unit_converter {
    typedef select_base_unit_converter<typename unscale<Source>::type, typename unscale<Dest>::type> selector;
    typedef typename selector::source_type source_type;
    typedef typename selector::destination_type destination_type;
    typedef base_unit_converter<source_type, destination_type> converter;
    typedef typename mpl::divides<typename get_scale_list<Source>::type, typename get_scale_list<source_type>::type>::type source_factor;
    typedef typename mpl::divides<typename get_scale_list<Dest>::type, typename get_scale_list<destination_type>::type>::type destination_factor;
    typedef typename mpl::divides<source_factor, destination_factor>::type factor;
    typedef eval_scale_list<factor> eval_factor;
    typedef typename multiply_typeof_helper<typename converter::type, typename eval_factor::type>::type type;
    static type value()
    {
        return(converter::value() * eval_factor::value());
    }
};

template<bool forward_is_defined, bool reverse_is_defined>
struct call_base_unit_converter_base_unit_impl;

template<>
struct call_base_unit_converter_base_unit_impl<true, true>
{
    template<class Source, class Dest>
    struct apply
        : do_call_base_unit_converter<Source, typename Dest::unit_type> 
    {
    };
};

template<>
struct call_base_unit_converter_base_unit_impl<true, false>
{
    template<class Source, class Dest>
    struct apply
        : do_call_base_unit_converter<Source, typename Dest::unit_type> 
    {
    };
};

template<>
struct call_base_unit_converter_base_unit_impl<false, true>
{
    template<class Source, class Dest>
    struct apply
    {
        typedef do_call_base_unit_converter<Dest, typename Source::unit_type> converter;
        typedef typename divide_typeof_helper<one, typename converter::type>::type type;
        static type value() {
            return(one() / converter::value());
        }
    };
};

template<>
struct call_base_unit_converter_base_unit_impl<false, false>
{
    template<class Source, class Dest>
    struct apply
    {
        typedef typename reduce_unit<typename get_default_conversion<Source>::type>::type new_source;
        typedef typename reduce_unit<typename get_default_conversion<Dest>::type>::type new_dest;
        typedef call_base_unit_converter<Source, new_source> start;
        typedef detail::conversion_factor_helper<
            new_source,
            new_dest
        > conversion;
        typedef call_base_unit_converter<Dest, new_dest> end;
        typedef typename divide_typeof_helper<
            typename multiply_typeof_helper<
                typename start::type,
                typename conversion::type
            >::type,
            typename end::type
        >::type type;
        static type value() {
            return(start::value() * conversion::value() / end::value());
        }
    };
};

template<int N>
struct get_default_conversion_impl
{
    template<class Begin>
    struct apply
    {
        typedef typename Begin::item source_pair;
        typedef typename source_pair::value_type exponent;
        typedef typename source_pair::tag_type source;
        typedef typename get_default_conversion<source>::type new_source;
        typedef typename get_default_conversion_impl<N-1>::template apply<typename Begin::next> next_iteration;
        typedef typename multiply_typeof_helper<typename power_typeof_helper<new_source, exponent>::type, typename next_iteration::unit_type>::type unit_type;
        typedef call_base_unit_converter<source, new_source> conversion;
        typedef typename multiply_typeof_helper<typename conversion::type, typename next_iteration::type>::type type;
        static type value() {
            return(static_rational_power<exponent>(conversion::value()) * next_iteration::value());
        }
    };
};

template<>
struct get_default_conversion_impl<0>
{
    template<class Begin>
    struct apply
    {
        typedef unit<dimensionless_type, heterogeneous_system<heterogeneous_system_impl<dimensionless_type, dimensionless_type, no_scale> > > unit_type;
        typedef one type;
        static type value() {
            return(type());
        }
    };
};

template<bool is_defined>
struct call_base_unit_converter_impl;

template<>
struct call_base_unit_converter_impl<true>
{
    template<class Source, class Dest>
    struct apply
        : do_call_base_unit_converter<Source, Dest> 
    {
    };
};

template<>
struct call_base_unit_converter_impl<false>
{
    template<class Source, class Dest>
    struct apply {
        typedef typename reduce_unit<typename get_default_conversion<Source>::type>::type new_source;
        typedef typename Dest::system_type::type system_list;
        typedef typename get_default_conversion_impl<system_list::size::value>::template apply<system_list> impl;
        typedef typename impl::unit_type new_dest;
        typedef call_base_unit_converter<Source, new_source> start;
        typedef conversion_factor_helper<new_source, new_dest> conversion;
        typedef typename divide_typeof_helper<
            typename multiply_typeof_helper<