Chris@16: // Copyright Alexander Nasonov & Paul A. Bristow 2006.
Chris@16: 
Chris@16: // Use, modification and distribution are subject to the
Chris@16: // Boost Software License, Version 1.0.
Chris@16: // (See accompanying file LICENSE_1_0.txt
Chris@16: // or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
Chris@16: #define BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
Chris@16: 
Chris@16: #include <climits>
Chris@16: #include <ios>
Chris@16: #include <limits>
Chris@16: 
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/integer_traits.hpp>
Chris@16: 
Chris@16: #ifndef BOOST_NO_IS_ABSTRACT
Chris@16: // Fix for SF:1358600 - lexical_cast & pure virtual functions & VC 8 STL
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: #include <boost/type_traits/is_abstract.hpp>
Chris@16: #endif
Chris@16: 
Chris@16: #if defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) || \
Chris@16:   (defined(BOOST_MSVC) && (BOOST_MSVC<1310))
Chris@16: 
Chris@16: #define BOOST_LCAST_NO_COMPILE_TIME_PRECISION
Chris@16: #endif
Chris@16: 
Chris@16: #ifdef BOOST_LCAST_NO_COMPILE_TIME_PRECISION
Chris@16: #include <boost/assert.hpp>
Chris@16: #else
Chris@16: #include <boost/static_assert.hpp>
Chris@16: #endif
Chris@16: 
Chris@16: namespace boost { namespace detail {
Chris@16: 
Chris@16: class lcast_abstract_stub {};
Chris@16: 
Chris@16: #ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION
Chris@16: // Calculate an argument to pass to std::ios_base::precision from
Chris@16: // lexical_cast. See alternative implementation for broken standard
Chris@16: // libraries in lcast_get_precision below. Keep them in sync, please.
Chris@16: template<class T>
Chris@16: struct lcast_precision
Chris@16: {
Chris@16: #ifdef BOOST_NO_IS_ABSTRACT
Chris@16:     typedef std::numeric_limits<T> limits; // No fix for SF:1358600.
Chris@16: #else
Chris@16:     typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_<
Chris@16:         boost::is_abstract<T>
Chris@16:       , std::numeric_limits<lcast_abstract_stub>
Chris@16:       , std::numeric_limits<T>
Chris@16:       >::type limits;
Chris@16: #endif
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(bool, use_default_precision =
Chris@16:             !limits::is_specialized || limits::is_exact
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(bool, is_specialized_bin =
Chris@16:             !use_default_precision &&
Chris@16:             limits::radix == 2 && limits::digits > 0
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(bool, is_specialized_dec =
Chris@16:             !use_default_precision &&
Chris@16:             limits::radix == 10 && limits::digits10 > 0
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(std::streamsize, streamsize_max =
Chris@16:             boost::integer_traits<std::streamsize>::const_max
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(unsigned int, precision_dec = limits::digits10 + 1U);
Chris@16: 
Chris@16:     BOOST_STATIC_ASSERT(!is_specialized_dec ||
Chris@16:             precision_dec <= streamsize_max + 0UL
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(unsigned long, precision_bin =
Chris@16:             2UL + limits::digits * 30103UL / 100000UL
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_ASSERT(!is_specialized_bin ||
Chris@16:             (limits::digits + 0UL < ULONG_MAX / 30103UL &&
Chris@16:             precision_bin > limits::digits10 + 0UL &&
Chris@16:             precision_bin <= streamsize_max + 0UL)
Chris@16:         );
Chris@16: 
Chris@16:     BOOST_STATIC_CONSTANT(std::streamsize, value =
Chris@16:             is_specialized_bin ? precision_bin
Chris@16:                                : is_specialized_dec ? precision_dec : 6
Chris@16:         );
Chris@16: };
Chris@16: #endif
Chris@16: 
Chris@16: template<class T>
Chris@16: inline std::streamsize lcast_get_precision(T* = 0)
Chris@16: {
Chris@16: #ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION
Chris@16:     return lcast_precision<T>::value;
Chris@16: #else // Follow lcast_precision algorithm at run-time:
Chris@16: 
Chris@16: #ifdef BOOST_NO_IS_ABSTRACT
Chris@16:     typedef std::numeric_limits<T> limits; // No fix for SF:1358600.
Chris@16: #else
Chris@16:     typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_<
Chris@16:         boost::is_abstract<T>
Chris@16:       , std::numeric_limits<lcast_abstract_stub>
Chris@16:       , std::numeric_limits<T>
Chris@16:       >::type limits;
Chris@16: #endif
Chris@16: 
Chris@16:     bool const use_default_precision =
Chris@16:         !limits::is_specialized || limits::is_exact;
Chris@16: 
Chris@16:     if(!use_default_precision)
Chris@16:     { // Includes all built-in floating-point types, float, double ...
Chris@16:       // and UDT types for which digits (significand bits) is defined (not zero)
Chris@16: 
Chris@16:         bool const is_specialized_bin =
Chris@16:             limits::radix == 2 && limits::digits > 0;
Chris@16:         bool const is_specialized_dec =
Chris@16:             limits::radix == 10 && limits::digits10 > 0;
Chris@16:         std::streamsize const streamsize_max =
Chris@16:             (boost::integer_traits<std::streamsize>::max)();
Chris@16: 
Chris@16:         if(is_specialized_bin)
Chris@16:         { // Floating-point types with
Chris@16:           // limits::digits defined by the specialization.
Chris@16: 
Chris@16:             unsigned long const digits = limits::digits;
Chris@16:             unsigned long const precision = 2UL + digits * 30103UL / 100000UL;
Chris@16:             // unsigned long is selected because it is at least 32-bits
Chris@16:             // and thus ULONG_MAX / 30103UL is big enough for all types.
Chris@16:             BOOST_ASSERT(
Chris@16:                     digits < ULONG_MAX / 30103UL &&
Chris@16:                     precision > limits::digits10 + 0UL &&
Chris@16:                     precision <= streamsize_max + 0UL
Chris@16:                 );
Chris@16:             return precision;
Chris@16:         }
Chris@16:         else if(is_specialized_dec)
Chris@16:         {   // Decimal Floating-point type, most likely a User Defined Type
Chris@16:             // rather than a real floating-point hardware type.
Chris@16:             unsigned int const precision = limits::digits10 + 1U;
Chris@16:             BOOST_ASSERT(precision <= streamsize_max + 0UL);
Chris@16:             return precision;
Chris@16:         }
Chris@16:     }
Chris@16: 
Chris@16:     // Integral type (for which precision has no effect)
Chris@16:     // or type T for which limits is NOT specialized,
Chris@16:     // so assume stream precision remains the default 6 decimal digits.
Chris@16:     // Warning: if your User-defined Floating-point type T is NOT specialized,
Chris@16:     // then you may lose accuracy by only using 6 decimal digits.
Chris@16:     // To avoid this, you need to specialize T with either
Chris@16:     // radix == 2 and digits == the number of significand bits,
Chris@16:     // OR
Chris@16:     // radix = 10 and digits10 == the number of decimal digits.
Chris@16: 
Chris@16:     return 6;
Chris@16: #endif
Chris@16: }
Chris@16: 
Chris@16: template<class T>
Chris@16: inline void lcast_set_precision(std::ios_base& stream, T*)
Chris@16: {
Chris@16:     stream.precision(lcast_get_precision<T>());
Chris@16: }
Chris@16: 
Chris@16: template<class Source, class Target>
Chris@16: inline void lcast_set_precision(std::ios_base& stream, Source*, Target*)
Chris@16: {
Chris@16:     std::streamsize const s = lcast_get_precision(static_cast<Source*>(0));
Chris@16:     std::streamsize const t = lcast_get_precision(static_cast<Target*>(0));
Chris@16:     stream.precision(s > t ? s : t);
Chris@16: }
Chris@16: 
Chris@16: }}
Chris@16: 
Chris@16: #endif //  BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
Chris@16: