converter.hpp

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//  (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: [e-mail]
//
#ifndef BOOST_NUMERIC_CONVERSION_DETAIL_CONVERTER_FLC_12NOV2002_HPP
#define BOOST_NUMERIC_CONVERSION_DETAIL_CONVERTER_FLC_12NOV2002_HPP

#include <functional>

#include "boost/numeric/conversion/detail/meta.hpp"
#include "boost/numeric/conversion/detail/conversion_traits.hpp"
#include "boost/numeric/conversion/bounds.hpp"

#include "boost/type_traits/is_same.hpp"

#include "boost/mpl/integral_c.hpp"

namespace boost { namespace numeric { namespace convdetail
{
  // Integral Constants representing rounding modes
  typedef mpl::integral_c<std::float_round_style, std::round_toward_zero>         round2zero_c ;
  typedef mpl::integral_c<std::float_round_style, std::round_to_nearest>          round2nearest_c ;
  typedef mpl::integral_c<std::float_round_style, std::round_toward_infinity>     round2inf_c ;
  typedef mpl::integral_c<std::float_round_style, std::round_toward_neg_infinity> round2neg_inf_c ;

  // Metafunction:
  //
  //   for_round_style<RoundStyle,RoundToZero,RoundToNearest,RoundToInf,RoundToNegInf>::type
  //
  // {RoundStyle} Integral Constant specifying a round style as declared above.
  // {RoundToZero,RoundToNearest,RoundToInf,RoundToNegInf} arbitrary types.
  //
  // Selects one of the 4 types according to the value of RoundStyle.
  //
  template<class RoundStyle,class RoundToZero,class RoundToNearest,class RoundToInf,class RoundToNegInf>
  struct for_round_style
  {
    typedef ct_switch4<RoundStyle
                       , round2zero_c, round2nearest_c, round2inf_c // round2neg_inf_c
                       , RoundToZero , RoundToNearest , RoundToInf , RoundToNegInf
                      > selector ;

    typedef typename selector::type type ;
  } ;


















//--------------------------------------------------------------------------
//                             Range Checking Logic.
//
// The range checking logic is built up by combining 1 or 2 predicates.
// Each predicate is encapsulated in a template class and exposes
// the static member function 'apply'.
//
//--------------------------------------------------------------------------


  // Because a particular logic can combine either 1 or two predicates, the following
  // tags are used to allow the predicate applier to receive 2 preds, but optimize away
  // one of them if it is 'non-applicable'
  struct non_applicable { typedef mpl::false_ do_apply ; } ;
  struct applicable     { typedef mpl::true_  do_apply ; } ;


  //--------------------------------------------------------------------------
  //
  //                      Range Checking Logic implementations.
  //
  // The following classes, collectivelly named 'Predicates', are instantiated within
  // the corresponding range checkers.
  // Their static member function 'apply' is called to perform the actual range checking logic.
  //--------------------------------------------------------------------------

    // s < Lowest(T) ? cNegOverflow : cInRange
    //
    template<class Traits>
    struct LT_LoT : applicable
    {
      typedef typename Traits::target_type T ;
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s < static_cast<S>(bounds<T>::lowest()) ? cNegOverflow : cInRange ;
      }
    } ;

    // s < 0 ? cNegOverflow : cInRange
    //
    template<class Traits>
    struct LT_Zero : applicable
    {
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s < static_cast<S>(0) ? cNegOverflow : cInRange ;
      }
    } ;

    // s <= Lowest(T)-1 ? cNegOverflow : cInRange
    //
    template<class Traits>
    struct LE_PrevLoT : applicable
    {
      typedef typename Traits::target_type T ;
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s <= static_cast<S>(bounds<T>::lowest()) - static_cast<S>(1.0)
                 ? cNegOverflow : cInRange ;
      }
    } ;

    // s < Lowest(T)-0.5 ? cNegOverflow : cInRange
    //
    template<class Traits>
    struct LT_HalfPrevLoT : applicable
    {
      typedef typename Traits::target_type T ;
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s < static_cast<S>(bounds<T>::lowest()) - static_cast<S>(0.5)
                 ? cNegOverflow : cInRange ;
      }
    } ;

    // s > Highest(T) ? cPosOverflow : cInRange
    //
    template<class Traits>
    struct GT_HiT : applicable
    {
      typedef typename Traits::target_type T ;
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s > static_cast<S>(bounds<T>::highest())
                 ? cPosOverflow : cInRange ;
      }
    } ;

    // s >= Lowest(T) + 1 ? cPosOverflow : cInRange
    //
    template<class Traits>
    struct GE_SuccHiT : applicable
    {
      typedef typename Traits::target_type T ;
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s >= static_cast<S>(bounds<T>::highest()) + static_cast<S>(1.0)
                 ? cPosOverflow : cInRange ;
      }
    } ;

    // s >= Lowest(T) + 0.5 ? cPosgOverflow : cInRange
    //
    template<class Traits>
    struct GT_HalfSuccHiT : applicable
    {
      typedef typename Traits::target_type T ;
      typedef typename Traits::source_type S ;
      typedef typename Traits::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        return s >= static_cast<S>(bounds<T>::highest()) + static_cast<S>(0.5)
                 ? cPosOverflow : cInRange ;
      }
    } ;


  //--------------------------------------------------------------------------
  //
  // Predicate Combiner.
  //
  // This helper classes are used to possibly combine the range checking logic
  // individually performed by the predicates
  //
  //--------------------------------------------------------------------------


    // Applies both predicates: first 'PredA', and if it equals 'cInRange', 'PredB'
    template<class PredA, class PredB>
    struct applyBoth
    {
      typedef typename PredA::argument_type argument_type ;

      static range_check_result apply ( argument_type s )
      {
        range_check_result r = PredA::apply(s) ;
        if ( r == cInRange )
          r = PredB::apply(s);
        return r ;
      }
    } ;

    template<class PredA, class PredB>
    struct combine
    {
      typedef applyBoth<PredA,PredB> Both ;
      typedef void                   NNone ; // 'None' is defined as a macro in (/usr/X11R6/include/X11/X.h)

      typedef typename PredA::do_apply do_applyA ;
      typedef typename PredB::do_apply do_applyB ;

      typedef typename for_both<do_applyA, do_applyB, Both, PredA, PredB, NNone>::type type ;
    } ;












//--------------------------------------------------------------------------
//                             Range Checker classes.
//
// The following classes are VISIBLE base classes of the user-level converter<> class.
// They supply the optimized 'out_of_range()' and 'validate_range()' static member functions
// visible in the user interface.
//
//--------------------------------------------------------------------------

  // Dummy range checker.
  template<class Traits>
  struct dummy_range_checker
  {
    typedef typename Traits::argument_type argument_type ;

    static range_check_result out_of_range ( argument_type ) { return cInRange ; }
    static void validate_range ( argument_type ) {}
  } ;

  // Generic range checker.
  //
  // All the range checking logic for all possible combinations of source and target
  // can be arranged in terms of one or two predicates, which test overflow on both neg/pos 'sides'
  // of the ranges.
  //
  // These predicates are given here as IsNegOverflow and IsPosOverflow.
  //
  template<class Traits, class IsNegOverflow, class IsPosOverflow, class OverflowHandler>
  struct generic_range_checker
  {
    typedef OverflowHandler overflow_handler ;

    typedef typename Traits::argument_type argument_type ;

    static range_check_result out_of_range ( argument_type s )
    {
      typedef typename combine<IsNegOverflow,IsPosOverflow>::type Predicate ;

      return Predicate::apply(s);
    }

    static void validate_range ( argument_type s )
      { OverflowHandler()( out_of_range(s) ) ; }
  } ;



//--------------------------------------------------------------------------
//
// Selectors for the optimized Range Checker class.
//