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// 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(static_cast<Source*>(0));
std::streamsize const t = lcast_get_precision(static_cast<Target*>(0));
stream.precision(s > t ? s : t);
}
}}
#endif // BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
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