//  © 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