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Filename : is_backend.hpp
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///////////////////////////////////////////////////////////////////////////////
//  Copyright 2015 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_IS_BACKEND_HPP
#define BOOST_MP_IS_BACKEND_HPP

#include <boost/mpl/has_xxx.hpp>
#include <boost/type_traits/conditional.hpp>
#include <boost/type_traits/is_convertible.hpp>
#include <boost/multiprecision/detail/number_base.hpp>

namespace boost { namespace multiprecision { namespace detail {

BOOST_MPL_HAS_XXX_TRAIT_DEF(signed_types)
BOOST_MPL_HAS_XXX_TRAIT_DEF(unsigned_types)
BOOST_MPL_HAS_XXX_TRAIT_DEF(float_types)

template <class T>
struct is_backend
{
   static const bool value = has_signed_types<T>::value && has_unsigned_types<T>::value && has_float_types<T>::value;
};

template <class Backend>
struct other_backend
{
   typedef typename boost::conditional<
       boost::is_same<number<Backend>, number<Backend, et_on> >::value,
       number<Backend, et_off>, number<Backend, et_on> >::type type;
};

template <class B, class V>
struct number_from_backend
{
   typedef typename boost::conditional<
       boost::is_convertible<V, number<B> >::value,
       number<B>,
       typename other_backend<B>::type>::type type;
};

template <bool b, class T, class U>
struct is_first_backend_imp
{
   static const bool value = false;
};
template <class T, class U>
struct is_first_backend_imp<true, T, U>
{
   static const bool value = is_convertible<U, number<T, et_on> >::value || is_convertible<U, number<T, et_off> >::value;
};

template <class T, class U>
struct is_first_backend : is_first_backend_imp<is_backend<T>::value, T, U>
{};

template <bool b, class T, class U>
struct is_second_backend_imp
{
   static const bool value = false;
};
template <class T, class U>
struct is_second_backend_imp<true, T, U>
{
   static const bool value = (is_convertible<T, number<U, et_on> >::value || is_convertible<T, number<U, et_off> >::value) && !is_first_backend<T, U>::value;
};

template <class T, class U>
struct is_second_backend : is_second_backend_imp<is_backend<U>::value, T, U>
{};

}
}
} // namespace boost::multiprecision::detail

#endif // BOOST_MP_IS_BACKEND_HPP