1 files changed, 63 insertions, 0 deletions
diff --git a/boost/multiprecision/traits/is_backend.hpp b/boost/multiprecision/traits/is_backend.hpp
new file mode 100644
index 0000000000..9b23c86665
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+++ b/boost/multiprecision/traits/is_backend.hpp
@@ -0,0 +1,63 @@
+///////////////////////////////////////////////////////////////////////////////
+//  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> {};
+
+}
+}
+}
+
+#endif // BOOST_MP_IS_BACKEND_HPP