// Copyright Alexander Nasonov & Paul A. Bristow 2006.



// Use, modification and distribution are 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)



#ifndef BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED

#define BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED



#include <climits>

#include <ios>

#include <limits>



#include <boost/config.hpp>

#include <boost/integer_traits.hpp>



#ifndef BOOST_NO_IS_ABSTRACT

// Fix for SF:1358600 - lexical_cast & pure virtual functions & VC 8 STL

#include <boost/mpl/if.hpp>

#include <boost/type_traits/is_abstract.hpp>

#endif



#if defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) || \

  (defined(BOOST_MSVC) && (BOOST_MSVC<1310))



#define BOOST_LCAST_NO_COMPILE_TIME_PRECISION

#endif



#ifdef BOOST_LCAST_NO_COMPILE_TIME_PRECISION

#include <boost/assert.hpp>

#else

#include <boost/static_assert.hpp>

#endif



namespace boost { namespace detail {



class lcast_abstract_stub {};



#ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION

// Calculate an argument to pass to std::ios_base::precision from

// lexical_cast. See alternative implementation for broken standard

// libraries in lcast_get_precision below. Keep them in sync, please.

template<class T>

struct lcast_precision

{

#ifdef BOOST_NO_IS_ABSTRACT

    typedef std::numeric_limits<T> limits; // No fix for SF:1358600.

#else

    typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_<

        boost::is_abstract<T>

      , std::numeric_limits<lcast_abstract_stub>

      , std::numeric_limits<T>

      >::type limits;

#endif



    BOOST_STATIC_CONSTANT(bool, use_default_precision =

            !limits::is_specialized || limits::is_exact

        );



    BOOST_STATIC_CONSTANT(bool, is_specialized_bin =

            !use_default_precision &&

            limits::radix == 2 && limits::digits > 0

        );



    BOOST_STATIC_CONSTANT(bool, is_specialized_dec =

            !use_default_precision &&

            limits::radix == 10 && limits::digits10 > 0

        );



    BOOST_STATIC_CONSTANT(std::streamsize, streamsize_max =

            boost::integer_traits<std::streamsize>::const_max

        );



    BOOST_STATIC_CONSTANT(unsigned int, precision_dec = limits::digits10 + 1U);



    BOOST_STATIC_ASSERT(!is_specialized_dec ||

            precision_dec <= streamsize_max + 0UL

        );



    BOOST_STATIC_CONSTANT(unsigned long, precision_bin =

            2UL + limits::digits * 30103UL / 100000UL

        );



    BOOST_STATIC_ASSERT(!is_specialized_bin ||

            (limits::digits + 0UL < ULONG_MAX / 30103UL &&

            precision_bin > limits::digits10 + 0UL &&

            precision_bin <= streamsize_max + 0UL)

        );



    BOOST_STATIC_CONSTANT(std::streamsize, value =

            is_specialized_bin ? precision_bin

                               : is_specialized_dec ? precision_dec : 6

        );

};

#endif



template<class T>

inline std::streamsize lcast_get_precision(T* = 0)

{

#ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION

    return lcast_precision<T>::value;

#else // Follow lcast_precision algorithm at run-time:



#ifdef BOOST_NO_IS_ABSTRACT

    typedef std::numeric_limits<T> limits; // No fix for SF:1358600.

#else

    typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_<

        boost::is_abstract<T>

      , std::numeric_limits<lcast_abstract_stub>

      , std::numeric_limits<T>

      >::type limits;

#endif



    bool const use_default_precision =

        !limits::is_specialized || limits::is_exact;



    if(!use_default_precision)

    { // Includes all built-in floating-point types, float, double ...

      // and UDT types for which digits (significand bits) is defined (not zero)



        bool const is_specialized_bin =

            limits::radix == 2 && limits::digits > 0;

        bool const is_specialized_dec =

            limits::radix == 10 && limits::digits10 > 0;

        std::streamsize const streamsize_max =

            (boost::integer_traits<std::streamsize>::max)();



        if(is_specialized_bin)

        { // Floating-point types with

          // limits::digits defined by the specialization.



            unsigned long const digits = limits::digits;

            unsigned long const precision = 2UL + digits * 30103UL / 100000UL;

            // unsigned long is selected because it is at least 32-bits

            // and thus ULONG_MAX / 30103UL is big enough for all types.

            BOOST_ASSERT(

                    digits < ULONG_MAX / 30103UL &&

                    precision > limits::digits10 + 0UL &&

                    precision <= streamsize_max + 0UL

                );

            return precision;

        }

        else if(is_specialized_dec)

        {   // Decimal Floating-point type, most likely a User Defined Type

            // rather than a real floating-point hardware type.

            unsigned int const precision = limits::digits10 + 1U;

            BOOST_ASSERT(precision <= streamsize_max + 0UL);

            return precision;

        }

    }



    // Integral type (for which precision has no effect)

    // or type T for which limits is NOT specialized,

    // so assume stream precision remains the default 6 decimal digits.

    // Warning: if your User-defined Floating-point type T is NOT specialized,

    // then you may lose accuracy by only using 6 decimal digits.

    // To avoid this, you need to specialize T with either

    // radix == 2 and digits == the number of significand bits,

    // OR

    // radix = 10 and digits10 == the number of decimal digits.



    return 6;

#endif

}



template<class T>

inline void lcast_set_precision(std::ios_base& stream, T*)

{

    stream.precision(lcast_get_precision<T>());

}



template<class Source, class Target>

inline void lcast_set_precision(std::ios_base& stream, Source*, Target*)

{

    std::streamsize const s = lcast_get_precision((Source*)0);

    std::streamsize const t = lcast_get_precision((Target*)0);

    stream.precision(s > t ? s : t);

}



}}



#endif //  BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED



