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