// (c) Copyright Fernando Luis Cacciola Carballal 2000-2004 // Use, modification, and distribution is subject to 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) // See library home page at http://www.boost.org/libs/numeric/conversion // // Contact the author at: fernando_cacciola@hotmail.com // #ifndef BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP #define BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP #include "boost/config.hpp" #include "boost/limits.hpp" #include "boost/mpl/int.hpp" #include "boost/mpl/multiplies.hpp" #include "boost/mpl/less.hpp" #include "boost/mpl/equal_to.hpp" #include "boost/type_traits/is_same.hpp" #include "boost/numeric/conversion/detail/meta.hpp" #include "boost/numeric/conversion/detail/int_float_mixture.hpp" #include "boost/numeric/conversion/detail/sign_mixture.hpp" #include "boost/numeric/conversion/detail/udt_builtin_mixture.hpp" namespace boost { namespace numeric { namespace convdetail { //--------------------------------------------------------------- // Implementations of the compile time predicate "T is subranged" //--------------------------------------------------------------- // for integral to integral conversions template<class T,class S> struct subranged_Sig2Unsig { // Signed to unsigned conversions are 'subranged' because of possible loose // of negative values. typedef mpl::true_ type ; } ; // for unsigned integral to signed integral conversions template<class T,class S> struct subranged_Unsig2Sig { // IMPORTANT NOTE: // // This code assumes that signed/unsigned integral values are represented // such that: // // numeric_limits<signed T>::digits + 1 == numeric_limits<unsigned T>::digits // // The '+1' is required since numeric_limits<>::digits gives 1 bit less for signed integral types. // // This fact is used by the following logic: // // if ( (numeric_limits<T>::digits+1) < (2*numeric_limits<S>::digits) ) // then the conversion is subranged. // typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ; typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ; // T is signed, so take digits+1 typedef typename T_digits::next u_T_digits ; typedef mpl::int_<2> Two ; typedef typename mpl::multiplies<S_digits,Two>::type S_digits_times_2 ; typedef typename mpl::less<u_T_digits,S_digits_times_2>::type type ; } ; // for integral to integral conversions of the same sign. template<class T,class S> struct subranged_SameSign { // An integral conversion of the same sign is subranged if digits(T) < digits(S). typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ; typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ; typedef typename mpl::less<T_digits,S_digits>::type type ; } ; // for integral to float conversions template<class T,class S> struct subranged_Int2Float { typedef mpl::false_ type ; } ; // for float to integral conversions template<class T,class S> struct subranged_Float2Int { typedef mpl::true_ type ; } ; // for float to float conversions template<class T,class S> struct subranged_Float2Float { // If both T and S are floats, // compare exponent bits and if they match, mantisa bits. typedef mpl::int_< ::std::numeric_limits<S>::digits > S_mantisa ; typedef mpl::int_< ::std::numeric_limits<T>::digits > T_mantisa ; typedef mpl::int_< ::std::numeric_limits<S>::max_exponent > S_exponent ; typedef mpl::int_< ::std::numeric_limits<T>::max_exponent > T_exponent ; typedef typename mpl::less<T_exponent,S_exponent>::type T_smaller_exponent ; typedef typename mpl::equal_to<T_exponent,S_exponent>::type equal_exponents ; typedef mpl::less<T_mantisa,S_mantisa> T_smaller_mantisa ; typedef mpl::eval_if<equal_exponents,T_smaller_mantisa,mpl::false_> not_bigger_exponent_case ; typedef typename mpl::eval_if<T_smaller_exponent,mpl::true_,not_bigger_exponent_case>::type type ; } ; // for Udt to built-in conversions template<class T,class S> struct subranged_Udt2BuiltIn { typedef mpl::true_ type ; } ; // for built-in to Udt conversions template<class T,class S> struct subranged_BuiltIn2Udt { typedef mpl::false_ type ; } ; // for Udt to Udt conversions template<class T,class S> struct subranged_Udt2Udt { typedef mpl::false_ type ; } ; //------------------------------------------------------------------- // Selectors for the implementations of the subranged predicate //------------------------------------------------------------------- template<class T,class S> struct get_subranged_Int2Int { typedef subranged_SameSign<T,S> Sig2Sig ; typedef subranged_Sig2Unsig<T,S> Sig2Unsig ; typedef subranged_Unsig2Sig<T,S> Unsig2Sig ; typedef Sig2Sig Unsig2Unsig ; typedef typename get_sign_mixture<T,S>::type sign_mixture ; typedef typename for_sign_mixture<sign_mixture, Sig2Sig, Sig2Unsig, Unsig2Sig, Unsig2Unsig>::type type ; } ; template<class T,class S> struct get_subranged_BuiltIn2BuiltIn { typedef get_subranged_Int2Int<T,S> Int2IntQ ; typedef subranged_Int2Float <T,S> Int2Float ; typedef subranged_Float2Int <T,S> Float2Int ; typedef subranged_Float2Float<T,S> Float2Float ; typedef mpl::identity<Int2Float > Int2FloatQ ; typedef mpl::identity<Float2Int > Float2IntQ ; typedef mpl::identity<Float2Float> Float2FloatQ ; typedef typename get_int_float_mixture<T,S>::type int_float_mixture ; typedef for_int_float_mixture<int_float_mixture, Int2IntQ, Int2FloatQ, Float2IntQ, Float2FloatQ> for_ ; typedef typename for_::type selected ; typedef typename selected::type type ; } ; template<class T,class S> struct get_subranged { typedef get_subranged_BuiltIn2BuiltIn<T,S> BuiltIn2BuiltInQ ; typedef subranged_BuiltIn2Udt<T,S> BuiltIn2Udt ; typedef subranged_Udt2BuiltIn<T,S> Udt2BuiltIn ; typedef subranged_Udt2Udt<T,S> Udt2Udt ; typedef mpl::identity<BuiltIn2Udt> BuiltIn2UdtQ ; typedef mpl::identity<Udt2BuiltIn> Udt2BuiltInQ ; typedef mpl::identity<Udt2Udt > Udt2UdtQ ; typedef typename get_udt_builtin_mixture<T,S>::type udt_builtin_mixture ; typedef typename for_udt_builtin_mixture<udt_builtin_mixture, BuiltIn2BuiltInQ, BuiltIn2UdtQ, Udt2BuiltInQ, Udt2UdtQ>::type selected ; typedef typename selected::type selected2 ; typedef typename selected2::type type ; } ; //------------------------------------------------------------------- // Top level implementation selector. //------------------------------------------------------------------- template<class T, class S> struct get_is_subranged { typedef get_subranged<T,S> non_trivial_case ; typedef mpl::identity<mpl::false_> trivial_case ; typedef is_same<T,S> is_trivial ; typedef typename mpl::if_<is_trivial,trivial_case,non_trivial_case>::type selected ; typedef typename selected::type type ; } ; } } } // namespace boost::numeric::convdetail #endif