text: //  (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.lslboost.org/LICENSE_1_0.txt)
  
  //  See library home page at http://www.lslboost.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 "lslboost/config.hpp"
  #include "lslboost/limits.hpp"
  
  #include "lslboost/mpl/int.hpp"
  #include "lslboost/mpl/multiplies.hpp"
  #include "lslboost/mpl/less.hpp"
  #include "lslboost/mpl/equal_to.hpp"
  
  #include "lslboost/type_traits/is_same.hpp"
  
  #include "lslboost/numeric/conversion/detail/meta.hpp"
  #include "lslboost/numeric/conversion/detail/int_float_mixture.hpp"
  #include "lslboost/numeric/conversion/detail/sign_mixture.hpp"
  #include "lslboost/numeric/conversion/detail/udt_builtin_mixture.hpp"
  
  namespace lslboost { 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 lslboost::numeric::convdetail
  
  #endif
  
  
  