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boost/cast.hpp

//  boost cast.hpp header file  ----------------------------------------------//

//  (C) Copyright Kevlin Henney and Dave Abrahams 1999. 
//  Distributed under 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 http://www.boost.org/libs/conversion for Documentation.

//  Revision History
//  02 Apr 01  Removed BOOST_NO_LIMITS workarounds and included 
//             <boost/limits.hpp> instead (the workaround did not 
//             actually compile when BOOST_NO_LIMITS was defined in 
//             any case, so we loose nothing). (John Maddock)
//  21 Jan 01  Undid a bug I introduced yesterday. numeric_cast<> never
//             worked with stock GCC; trying to get it to do that broke
//             vc-stlport.
//  20 Jan 01  Moved BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS to config.hpp.
//             Removed unused BOOST_EXPLICIT_TARGET macro. Moved
//             boost::detail::type to boost/type.hpp. Made it compile with
//             stock gcc again (Dave Abrahams)
//  29 Nov 00  Remove nested namespace cast, cleanup spacing before Formal
//             Review (Beman Dawes)
//  19 Oct 00  Fix numeric_cast for floating-point types (Dave Abrahams)
//  15 Jul 00  Suppress numeric_cast warnings for GCC, Borland and MSVC
//             (Dave Abrahams)
//  30 Jun 00  More MSVC6 wordarounds.  See comments below.  (Dave Abrahams)
//  28 Jun 00  Removed implicit_cast<>.  See comment below. (Beman Dawes)
//  27 Jun 00  More MSVC6 workarounds 
//  15 Jun 00  Add workarounds for MSVC6
//   2 Feb 00  Remove bad_numeric_cast ";" syntax error (Doncho Angelov)
//  26 Jan 00  Add missing throw() to bad_numeric_cast::what(0 (Adam Levar)
//  29 Dec 99  Change using declarations so usages in other namespaces work
//             correctly (Dave Abrahams)
//  23 Sep 99  Change polymorphic_downcast assert to also detect M.I. errors
//             as suggested Darin Adler and improved by Valentin Bonnard.  
//   2 Sep 99  Remove controversial asserts, simplify, rename.
//  30 Aug 99  Move to cast.hpp, replace value_cast with numeric_cast,
//             place in nested namespace.
//   3 Aug 99  Initial version

#ifndef BOOST_CAST_HPP
#define BOOST_CAST_HPP

# include <boost/config.hpp>
# include <cassert>
# include <typeinfo>
# include <boost/type.hpp>
# include <boost/limits.hpp>
# include <boost/detail/select_type.hpp>

//  It has been demonstrated numerous times that MSVC 6.0 fails silently at link
//  time if you use a template function which has template parameters that don't
//  appear in the function's argument list.
//
//  TODO: Add this to config.hpp?
# if defined(BOOST_MSVC) && BOOST_MSVC <= 1200 // 1200 = VC6
#  define BOOST_EXPLICIT_DEFAULT_TARGET , ::boost::type<Target>* = 0
# else
#  define BOOST_EXPLICIT_DEFAULT_TARGET
# endif

namespace boost
{
//  See the documentation for descriptions of how to choose between
//  static_cast<>, dynamic_cast<>, polymorphic_cast<> and polymorphic_downcast<>

//  polymorphic_cast  --------------------------------------------------------//

    //  Runtime checked polymorphic downcasts and crosscasts.
    //  Suggested in The C++ Programming Language, 3rd Ed, Bjarne Stroustrup, 
    //  section 15.8 exercise 1, page 425.

    template <class Target, class Source>
    inline Target polymorphic_cast(Source* x BOOST_EXPLICIT_DEFAULT_TARGET)
    {
        Target tmp = dynamic_cast<Target>(x);
        if ( tmp == 0 ) throw std::bad_cast();
        return tmp;
    }

//  polymorphic_downcast  ----------------------------------------------------//

    //  assert() checked polymorphic downcast.  Crosscasts prohibited.

    //  WARNING: Because this cast uses assert(), it violates the One Definition
    //  Rule if NDEBUG is inconsistently defined across translation units.

    //  Contributed by Dave Abrahams

    template <class Target, class Source>
    inline Target polymorphic_downcast(Source* x BOOST_EXPLICIT_DEFAULT_TARGET)
    {
        assert( dynamic_cast<Target>(x) == x );  // detect logic error
        return static_cast<Target>(x);
    }

//  implicit_cast  -----------------------------------------------------------//
//
//  Removed due to uncertain purpose.  Use either numeric_cast (see below)
//  or static_cast according to the need. 

//  numeric_cast and related exception  --------------------------------------//

//  Contributed by Kevlin Henney

//  bad_numeric_cast  --------------------------------------------------------//

    // exception used to indicate runtime numeric_cast failure
    class bad_numeric_cast : public std::bad_cast
    {
    public:
        // constructors, destructors and assignment operator defaulted

        // function inlined for brevity and consistency with rest of library
        virtual const char *what() const throw()
        {
            return "bad numeric cast: loss of range in numeric_cast";
        }
    };

//  numeric_cast  ------------------------------------------------------------//

#if !defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) || defined(BOOST_SGI_CPP_LIMITS)
  
    namespace detail
    {
      template <class T>
      struct signed_numeric_limits : std::numeric_limits<T>
      {
             static inline T min BOOST_PREVENT_MACRO_SUBSTITUTION ()
         {
             return (std::numeric_limits<T>::min)() >= 0
                     // unary minus causes integral promotion, thus the static_cast<>
                     ? static_cast<T>(-(std::numeric_limits<T>::max)())
                     : (std::numeric_limits<T>::min)();
         };
      };
   
      // Move to namespace boost in utility.hpp?
      template <class T, bool specialized>
      struct fixed_numeric_limits_base
          : public if_true< std::numeric_limits<T>::is_signed >
           ::BOOST_NESTED_TEMPLATE then< signed_numeric_limits<T>,
                            std::numeric_limits<T>
                   >::type
      {};
      
      template <class T>
      struct fixed_numeric_limits
          : fixed_numeric_limits_base<T,(std::numeric_limits<T>::is_specialized)>
      {};

# ifdef BOOST_HAS_LONG_LONG
      // cover implementations which supply no specialization for long
      // long / unsigned long long. Not intended to be full
      // numeric_limits replacements, but good enough for numeric_cast<>
      template <>
      struct fixed_numeric_limits_base< ::boost::long_long_type, false>
      {
          BOOST_STATIC_CONSTANT(bool, is_specialized = true);
          BOOST_STATIC_CONSTANT(bool, is_signed = true);
          static  ::boost::long_long_type max BOOST_PREVENT_MACRO_SUBSTITUTION ()
          {
#  ifdef LONGLONG_MAX
              return LONGLONG_MAX;
#  else
              return 9223372036854775807LL; // hope this is portable
#  endif 
          }

          static  ::boost::long_long_type min BOOST_PREVENT_MACRO_SUBSTITUTION ()
          {
#  ifdef LONGLONG_MIN
              return LONGLONG_MIN;
#  else  
               return -( 9223372036854775807LL )-1; // hope this is portable
#  endif 
          }
      };

      template <>
      struct fixed_numeric_limits_base< ::boost::ulong_long_type, false>
      {
          BOOST_STATIC_CONSTANT(bool, is_specialized = true);
          BOOST_STATIC_CONSTANT(bool, is_signed = false);
          static  ::boost::ulong_long_type max BOOST_PREVENT_MACRO_SUBSTITUTION ()
          {
#  ifdef ULONGLONG_MAX
              return ULONGLONG_MAX;
#  else
              return 0xffffffffffffffffULL; // hope this is portable
#  endif 
          }

          static  ::boost::ulong_long_type min BOOST_PREVENT_MACRO_SUBSTITUTION () { return 0; }
      };
# endif 
    } // namespace detail
  
// less_than_type_min -
  //    x_is_signed should be numeric_limits<X>::is_signed
  //    y_is_signed should be numeric_limits<Y>::is_signed
  //    y_min should be numeric_limits<Y>::min()
  //
  //    check(x, y_min) returns true iff x < y_min without invoking comparisons
  //    between signed and unsigned values.
  //
  //    "poor man's partial specialization" is in use here.
    template <bool x_is_signed, bool y_is_signed>
    struct less_than_type_min
    {
        template <class X, class Y>
        static bool check(X x, Y y_min)
            { return x < y_min; }
    };

    template <>
    struct less_than_type_min<false, true>
    {
        template <class X, class Y>
        static bool check(X, Y)
            { return false; }
    };
    
    template <>
    struct less_than_type_min<true, false>
    {
        template <class X, class Y>
        static bool check(X x, Y)
            { return x < 0; }
    };
    
  // greater_than_type_max -
  //    same_sign should be:
  //            numeric_limits<X>::is_signed == numeric_limits<Y>::is_signed
  //    y_max should be numeric_limits<Y>::max()
  //
  //    check(x, y_max) returns true iff x > y_max without invoking comparisons
  //    between signed and unsigned values.
  //
  //    "poor man's partial specialization" is in use here.
    template <bool same_sign, bool x_is_signed>
    struct greater_than_type_max;

    template<>
    struct greater_than_type_max<true, true>
    {
        template <class X, class Y>
        static inline bool check(X x, Y y_max)
            { return x > y_max; }
    };

    template <>
    struct greater_than_type_max<false, true>
    {
        // What does the standard say about this? I think it's right, and it
        // will work with every compiler I know of.
        template <class X, class Y>
        static inline bool check(X x, Y)
            { return x >= 0 && static_cast<X>(static_cast<Y>(x)) != x; }
        
# if defined(BOOST_MSVC) && BOOST_MSVC <= 1200
        // MSVC6 can't static_cast  unsigned __int64 -> floating types
#  define BOOST_UINT64_CAST(src_type)                                   \
        static inline bool check(src_type x, unsigned __int64)          \
        {                                                               \
            if (x < 0) return false;                                    \
            unsigned __int64 y = static_cast<unsigned __int64>(x);      \
            bool odd = y & 0x1;                                         \
            __int64 div2 = static_cast<__int64>(y >> 1);                \
            return ((static_cast<src_type>(div2) * 2.0) + odd) != x;    \
        }

        BOOST_UINT64_CAST(long double);
        BOOST_UINT64_CAST(double);
        BOOST_UINT64_CAST(float);
#  undef BOOST_UINT64_CAST
# endif 
    };

    template<>
    struct greater_than_type_max<true, false>
    {
        template <class X, class Y>
        static inline bool check(X x, Y y_max)
            { return x > y_max; }
    };

    template <>
    struct greater_than_type_max<false, false>
    {
        // What does the standard say about this? I think it's right, and it
        // will work with every compiler I know of.
        template <class X, class Y>
        static inline bool check(X x, Y)
            { return static_cast<X>(static_cast<Y>(x)) != x; }
    };
  
#else // use #pragma hacks if available

  namespace detail
  {
# if BOOST_MSVC
#  pragma warning(push)
#  pragma warning(disable : 4018)
#  pragma warning(disable : 4146)
#elif defined(__BORLANDC__)
#  pragma option push -w-8041
# endif

       // Move to namespace boost in utility.hpp?
       template <class T>
       struct fixed_numeric_limits : public std::numeric_limits<T>
       {
           static inline T min BOOST_PREVENT_MACRO_SUBSTITUTION ()
           {
               return std::numeric_limits<T>::is_signed && (std::numeric_limits<T>::min)() >= 0
                   ? T(-(std::numeric_limits<T>::max)()) : (std::numeric_limits<T>::min)();
           }
       };
  
# if BOOST_MSVC
#  pragma warning(pop)
#elif defined(__BORLANDC__)
#  pragma option pop
# endif
  } // namespace detail
  
#endif
  
    template<typename Target, typename Source>
    inline Target numeric_cast(Source arg BOOST_EXPLICIT_DEFAULT_TARGET)
    {
        // typedefs abbreviating respective trait classes
        typedef detail::fixed_numeric_limits<Source> arg_traits;
        typedef detail::fixed_numeric_limits<Target> result_traits;
        
#if defined(BOOST_STRICT_CONFIG) \
    || (!defined(__HP_aCC) || __HP_aCC > 33900) \
         && (!defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) \
             || defined(BOOST_SGI_CPP_LIMITS))
        // typedefs that act as compile time assertions
        // (to be replaced by boost compile time assertions
        // as and when they become available and are stable)
        typedef bool argument_must_be_numeric[arg_traits::is_specialized];
        typedef bool result_must_be_numeric[result_traits::is_specialized];

        const bool arg_is_signed = arg_traits::is_signed;
        const bool result_is_signed = result_traits::is_signed;
        const bool same_sign = arg_is_signed == result_is_signed;

        if (less_than_type_min<arg_is_signed, result_is_signed>::check(arg, (result_traits::min)())
            || greater_than_type_max<same_sign, arg_is_signed>::check(arg, (result_traits::max)())
            )
            
#else // We need to use #pragma hacks if available
            
# if BOOST_MSVC
#  pragma warning(push)
#  pragma warning(disable : 4018)
#elif defined(__BORLANDC__)
#pragma option push -w-8012
# endif
        if ((arg < 0 && !result_traits::is_signed)  // loss of negative range
             || (arg_traits::is_signed && arg < (result_traits::min)())  // underflow
             || arg > (result_traits::max)())            // overflow
# if BOOST_MSVC
#  pragma warning(pop)
#elif defined(__BORLANDC__)
#pragma option pop
# endif
#endif
        {
            throw bad_numeric_cast();
        }
        return static_cast<Target>(arg);
    } // numeric_cast

#  undef BOOST_EXPLICIT_DEFAULT_TARGET

} // namespace boost

#endif  // BOOST_CAST_HPP