Boost C++ Libraries

boost/multiprecision/traits/is_backend.hpp

///////////////////////////////////////////////////////////////////////////////
//  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 <type_traits>
#include <boost/multiprecision/detail/number_base.hpp>

namespace boost { namespace multiprecision { namespace detail {

template <class T>
struct has_signed_types
{
   template <class U>
   static double check(U*, typename U::signed_types* = nullptr);
   static char   check(...);
   static T* get();
   static constexpr bool value = sizeof(check(get())) == sizeof(double);
};
template <class T>
struct has_unsigned_types
{
   template <class U>
   static double check(U*, typename U::unsigned_types* = nullptr);
   static char   check(...);
   static T* get();
   static constexpr bool value = sizeof(check(get())) == sizeof(double);
};
template <class T>
struct has_float_types
{
   template <class U>
   static double check(U*, typename U::float_types* = nullptr);
   static char   check(...);
   static T* get();
   static constexpr bool value = sizeof(check(get())) == sizeof(double);
};

template <class T>
struct is_backend : public std::integral_constant<bool, has_signed_types<T>::value && has_unsigned_types<T>::value && has_float_types<T>::value> {};

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

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

template <bool b, class T, class U>
struct is_first_backend_imp : public std::false_type {};

template <class T, class U>
    struct is_first_backend_imp<true, T, U> : public std::integral_constant < bool, std::is_convertible<U, number<T, et_on> >::value || std::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 constexpr bool value = false;
};
template <class T, class U>
struct is_second_backend_imp<true, T, U>
{
   static constexpr bool value = (std::is_convertible<T, number<U, et_on> >::value || std::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