// 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 | |