williamr@2: //  © Copyright Fernando Luis Cacciola Carballal 2000-2004
williamr@2: //  Use, modification, and distribution is subject to the Boost Software
williamr@2: //  License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
williamr@2: //  http://www.boost.org/LICENSE_1_0.txt)
williamr@2: 
williamr@2: //  See library home page at http://www.boost.org/libs/numeric/conversion
williamr@2: //
williamr@2: // Contact the author at: fernando_cacciola@hotmail.com
williamr@2: // 
williamr@2: #ifndef BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
williamr@2: #define BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
williamr@2: 
williamr@2: #include "boost/config.hpp"
williamr@2: #include "boost/limits.hpp"
williamr@2: 
williamr@2: #include "boost/mpl/int.hpp"
williamr@2: #include "boost/mpl/multiplies.hpp"
williamr@2: #include "boost/mpl/less.hpp"
williamr@2: #include "boost/mpl/equal_to.hpp"
williamr@2: 
williamr@2: #include "boost/type_traits/is_same.hpp"
williamr@2: 
williamr@2: #include "boost/numeric/conversion/detail/meta.hpp"
williamr@2: #include "boost/numeric/conversion/detail/int_float_mixture.hpp"
williamr@2: #include "boost/numeric/conversion/detail/sign_mixture.hpp"
williamr@2: #include "boost/numeric/conversion/detail/udt_builtin_mixture.hpp"
williamr@2: 
williamr@2: namespace boost { namespace numeric { namespace convdetail
williamr@2: {
williamr@2:   //---------------------------------------------------------------
williamr@2:   // Implementations of the compile time predicate "T is subranged"
williamr@2:   //---------------------------------------------------------------
williamr@2: 
williamr@2:     // for integral to integral conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Sig2Unsig
williamr@2:     {
williamr@2:       // Signed to unsigned conversions are 'subranged' because of possible loose
williamr@2:       // of negative values.
williamr@2:       typedef mpl::true_ type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for unsigned integral to signed integral conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Unsig2Sig
williamr@2:     {
williamr@2:        // IMPORTANT NOTE:
williamr@2:        //
williamr@2:        // This code assumes that signed/unsigned integral values are represented
williamr@2:        // such that:
williamr@2:        //
williamr@2:        //  numeric_limits<signed T>::digits + 1 == numeric_limits<unsigned T>::digits
williamr@2:        //
williamr@2:        // The '+1' is required since numeric_limits<>::digits gives 1 bit less for signed integral types.
williamr@2:        //
williamr@2:        // This fact is used by the following logic:
williamr@2:        //
williamr@2:        //  if ( (numeric_limits<T>::digits+1) < (2*numeric_limits<S>::digits) )
williamr@2:        //    then the conversion is subranged.
williamr@2:        //
williamr@2: 
williamr@2:        typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
williamr@2:        typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
williamr@2: 
williamr@2:        // T is signed, so take digits+1
williamr@2:        typedef typename T_digits::next u_T_digits ;
williamr@2: 
williamr@2:        typedef mpl::int_<2> Two ;
williamr@2: 
williamr@2:        typedef typename mpl::multiplies<S_digits,Two>::type S_digits_times_2 ;
williamr@2: 
williamr@2:        typedef typename mpl::less<u_T_digits,S_digits_times_2>::type type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for integral to integral conversions of the same sign.
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_SameSign
williamr@2:     {
williamr@2:        // An integral conversion of the same sign is subranged if digits(T) < digits(S).
williamr@2: 
williamr@2:        typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
williamr@2:        typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
williamr@2: 
williamr@2:        typedef typename mpl::less<T_digits,S_digits>::type type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for integral to float conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Int2Float
williamr@2:     {
williamr@2:       typedef mpl::false_ type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for float to integral conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Float2Int
williamr@2:     {
williamr@2:       typedef mpl::true_ type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for float to float conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Float2Float
williamr@2:     {
williamr@2:       // If both T and S are floats,
williamr@2:       // compare exponent bits and if they match, mantisa bits.
williamr@2: 
williamr@2:       typedef mpl::int_< ::std::numeric_limits<S>::digits > S_mantisa ;
williamr@2:       typedef mpl::int_< ::std::numeric_limits<T>::digits > T_mantisa ;
williamr@2: 
williamr@2:       typedef mpl::int_< ::std::numeric_limits<S>::max_exponent > S_exponent ;
williamr@2:       typedef mpl::int_< ::std::numeric_limits<T>::max_exponent > T_exponent ;
williamr@2: 
williamr@2:       typedef typename mpl::less<T_exponent,S_exponent>::type T_smaller_exponent ;
williamr@2: 
williamr@2:       typedef typename mpl::equal_to<T_exponent,S_exponent>::type equal_exponents ;
williamr@2: 
williamr@2:       typedef mpl::less<T_mantisa,S_mantisa> T_smaller_mantisa ;
williamr@2: 
williamr@2:       typedef mpl::eval_if<equal_exponents,T_smaller_mantisa,mpl::false_> not_bigger_exponent_case ;
williamr@2: 
williamr@2:       typedef typename
williamr@2:         mpl::eval_if<T_smaller_exponent,mpl::true_,not_bigger_exponent_case>::type
williamr@2:           type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for Udt to built-in conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Udt2BuiltIn
williamr@2:     {
williamr@2:       typedef mpl::true_ type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for built-in to Udt conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_BuiltIn2Udt
williamr@2:     {
williamr@2:       typedef mpl::false_ type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     // for Udt to Udt conversions
williamr@2:     template<class T,class S>
williamr@2:     struct subranged_Udt2Udt
williamr@2:     {
williamr@2:       typedef mpl::false_ type ;
williamr@2:     } ;
williamr@2: 
williamr@2:   //-------------------------------------------------------------------
williamr@2:   // Selectors for the implementations of the subranged predicate
williamr@2:   //-------------------------------------------------------------------
williamr@2: 
williamr@2:     template<class T,class S>
williamr@2:     struct get_subranged_Int2Int
williamr@2:     {
williamr@2:       typedef subranged_SameSign<T,S>  Sig2Sig     ;
williamr@2:       typedef subranged_Sig2Unsig<T,S> Sig2Unsig   ;
williamr@2:       typedef subranged_Unsig2Sig<T,S> Unsig2Sig   ;
williamr@2:       typedef Sig2Sig                  Unsig2Unsig ;
williamr@2: 
williamr@2:       typedef typename get_sign_mixture<T,S>::type sign_mixture ;
williamr@2: 
williamr@2:       typedef typename
williamr@2:         for_sign_mixture<sign_mixture, Sig2Sig, Sig2Unsig, Unsig2Sig, Unsig2Unsig>::type
williamr@2:            type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     template<class T,class S>
williamr@2:     struct get_subranged_BuiltIn2BuiltIn
williamr@2:     {
williamr@2:       typedef get_subranged_Int2Int<T,S> Int2IntQ ;
williamr@2: 
williamr@2:       typedef subranged_Int2Float  <T,S> Int2Float   ;
williamr@2:       typedef subranged_Float2Int  <T,S> Float2Int   ;
williamr@2:       typedef subranged_Float2Float<T,S> Float2Float ;
williamr@2: 
williamr@2:       typedef mpl::identity<Int2Float  > Int2FloatQ   ;
williamr@2:       typedef mpl::identity<Float2Int  > Float2IntQ   ;
williamr@2:       typedef mpl::identity<Float2Float> Float2FloatQ ;
williamr@2: 
williamr@2:       typedef typename get_int_float_mixture<T,S>::type int_float_mixture ;
williamr@2: 
williamr@2:       typedef for_int_float_mixture<int_float_mixture, Int2IntQ, Int2FloatQ, Float2IntQ, Float2FloatQ> for_ ;
williamr@2: 
williamr@2:       typedef typename for_::type selected ;
williamr@2: 
williamr@2:       typedef typename selected::type type ;
williamr@2:     } ;
williamr@2: 
williamr@2:     template<class T,class S>
williamr@2:     struct get_subranged
williamr@2:     {
williamr@2:       typedef get_subranged_BuiltIn2BuiltIn<T,S> BuiltIn2BuiltInQ ;
williamr@2: 
williamr@2:       typedef subranged_BuiltIn2Udt<T,S> BuiltIn2Udt ;
williamr@2:       typedef subranged_Udt2BuiltIn<T,S> Udt2BuiltIn ;
williamr@2:       typedef subranged_Udt2Udt<T,S>     Udt2Udt ;
williamr@2: 
williamr@2:       typedef mpl::identity<BuiltIn2Udt> BuiltIn2UdtQ ;
williamr@2:       typedef mpl::identity<Udt2BuiltIn> Udt2BuiltInQ ;
williamr@2:       typedef mpl::identity<Udt2Udt    > Udt2UdtQ     ;
williamr@2: 
williamr@2:       typedef typename get_udt_builtin_mixture<T,S>::type udt_builtin_mixture ;
williamr@2:       
williamr@2:       typedef typename
williamr@2:         for_udt_builtin_mixture<udt_builtin_mixture, BuiltIn2BuiltInQ, BuiltIn2UdtQ, Udt2BuiltInQ, Udt2UdtQ>::type
williamr@2:           selected ;
williamr@2: 
williamr@2:       typedef typename selected::type selected2 ;
williamr@2:  
williamr@2:       typedef typename selected2::type type ;
williamr@2:     } ;
williamr@2: 
williamr@2: 
williamr@2:   //-------------------------------------------------------------------
williamr@2:   // Top level implementation selector.
williamr@2:   //-------------------------------------------------------------------
williamr@2:   template<class T, class S>
williamr@2:   struct get_is_subranged
williamr@2:   {
williamr@2:     typedef get_subranged<T,S>         non_trivial_case ;
williamr@2:     typedef mpl::identity<mpl::false_> trivial_case ;
williamr@2: 
williamr@2:     typedef is_same<T,S> is_trivial ;
williamr@2:    
williamr@2:     typedef typename mpl::if_<is_trivial,trivial_case,non_trivial_case>::type selected ;
williamr@2:     
williamr@2:     typedef typename selected::type type ;
williamr@2:   } ;
williamr@2: 
williamr@2: } } } // namespace boost::numeric::convdetail
williamr@2: 
williamr@2: #endif
williamr@2: 
williamr@2: