text: ///////////////////////////////////////////////////////////////////////////////
  //  Copyright Vicente J. Botet Escriba 2009-2011
  //  Copyright 2012 John Maddock. 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_MP_EXPLICIT_CONVERTIBLE_HPP
  #define BOOST_MP_EXPLICIT_CONVERTIBLE_HPP
  
  #include <boost/config.hpp>
  #include <boost/multiprecision/detail/number_base.hpp> // number_category
  #include <boost/type_traits/conditional.hpp>
  #include <boost/type_traits/declval.hpp>
  #include <boost/type_traits/integral_constant.hpp>
  #include <boost/type_traits/is_convertible.hpp>
  
  namespace boost {
  namespace multiprecision {
  namespace detail {
  
  template <unsigned int N> struct dummy_size {};
  
  template <typename S, typename T> struct has_generic_interconversion {
    typedef typename boost::conditional<
        is_number<S>::value && is_number<T>::value,
        typename boost::conditional<
            number_category<S>::value == number_kind_integer,
            typename boost::conditional<
                number_category<T>::value == number_kind_integer ||
                    number_category<T>::value == number_kind_floating_point ||
                    number_category<T>::value == number_kind_rational ||
                    number_category<T>::value == number_kind_fixed_point,
                boost::true_type, boost::false_type>::type,
            typename boost::conditional<
                number_category<S>::value == number_kind_rational,
                typename boost::conditional<
                    number_category<T>::value == number_kind_rational ||
                        number_category<T>::value == number_kind_rational,
                    boost::true_type, boost::false_type>::type,
                typename boost::conditional<
                    number_category<T>::value == number_kind_floating_point,
                    boost::true_type, boost::false_type>::type>::type>::type,
        boost::false_type>::type type;
  };
  
  template <typename S, typename T> struct is_explicitly_convertible_imp {
  #ifndef BOOST_NO_SFINAE_EXPR
    template <typename S1, typename T1>
    static type_traits::yes_type selector(dummy_size<sizeof(new T1(boost::declval<
  #if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
                                                                   S1
  #else
                                                                   S1 const &
  #endif
                                                                   >()))> *);
  
    template <typename S1, typename T1> static type_traits::no_type selector(...);
  
    static const bool value =
        sizeof(selector<S, T>(0)) == sizeof(type_traits::yes_type);
  
    typedef boost::integral_constant<bool, value> type;
  #else
    typedef typename has_generic_interconversion<S, T>::type gen_type;
    typedef boost::integral_constant<bool, boost::is_convertible<S, T>::value ||
                                               gen_type::value>
        type;
  #endif
  };
  
  template <typename From, typename To>
  struct is_explicitly_convertible
      : public is_explicitly_convertible_imp<From, To>::type {};
  
  #ifdef BOOST_NO_SFINAE_EXPR
  template <class Backend1, expression_template_option ExpressionTemplates1,
            class Backend2, expression_template_option ExpressionTemplates2>
  struct is_explicitly_convertible<number<Backend1, ExpressionTemplates1>,
                                   number<Backend2, ExpressionTemplates2>>
      : public is_explicitly_convertible<Backend1, Backend2> {};
  #endif
  
  } // namespace detail
  } // namespace multiprecision
  } // namespace boost
  
  #endif
  