Line data    Source code

       1             : // Copyright Alexander Nasonov & Paul A. Bristow 2006.
       2             : 
       3             : // Use, modification and distribution are subject to the
       4             : // Boost Software License, Version 1.0.
       5             : // (See accompanying file LICENSE_1_0.txt
       6             : // or copy at http://www.boost.org/LICENSE_1_0.txt)
       7             : 
       8             : #ifndef BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
       9             : #define BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
      10             : 
      11             : #include <climits>
      12             : #include <ios>
      13             : #include <limits>
      14             : 
      15             : #include <boost/config.hpp>
      16             : #include <boost/integer_traits.hpp>
      17             : 
      18             : #ifndef BOOST_NO_IS_ABSTRACT
      19             : // Fix for SF:1358600 - lexical_cast & pure virtual functions & VC 8 STL
      20             : #include <boost/type_traits/conditional.hpp>
      21             : #include <boost/type_traits/is_abstract.hpp>
      22             : #endif
      23             : 
      24             : #if defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) || \
      25             :   (defined(BOOST_MSVC) && (BOOST_MSVC<1310))
      26             : 
      27             : #define BOOST_LCAST_NO_COMPILE_TIME_PRECISION
      28             : #endif
      29             : 
      30             : #ifdef BOOST_LCAST_NO_COMPILE_TIME_PRECISION
      31             : #include <boost/assert.hpp>
      32             : #else
      33             : #include <boost/static_assert.hpp>
      34             : #endif
      35             : 
      36             : namespace boost { namespace detail {
      37             : 
      38             : class lcast_abstract_stub {};
      39             : 
      40             : #ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION
      41             : // Calculate an argument to pass to std::ios_base::precision from
      42             : // lexical_cast. See alternative implementation for broken standard
      43             : // libraries in lcast_get_precision below. Keep them in sync, please.
      44             : template<class T>
      45             : struct lcast_precision
      46             : {
      47             : #ifdef BOOST_NO_IS_ABSTRACT
      48             :     typedef std::numeric_limits<T> limits; // No fix for SF:1358600.
      49             : #else
      50             :     typedef BOOST_DEDUCED_TYPENAME boost::conditional<
      51             :         boost::is_abstract<T>::value
      52             :       , std::numeric_limits<lcast_abstract_stub>
      53             :       , std::numeric_limits<T>
      54             :       >::type limits;
      55             : #endif
      56             : 
      57             :     BOOST_STATIC_CONSTANT(bool, use_default_precision =
      58             :             !limits::is_specialized || limits::is_exact
      59             :         );
      60             : 
      61             :     BOOST_STATIC_CONSTANT(bool, is_specialized_bin =
      62             :             !use_default_precision &&
      63             :             limits::radix == 2 && limits::digits > 0
      64             :         );
      65             : 
      66             :     BOOST_STATIC_CONSTANT(bool, is_specialized_dec =
      67             :             !use_default_precision &&
      68             :             limits::radix == 10 && limits::digits10 > 0
      69             :         );
      70             : 
      71             :     BOOST_STATIC_CONSTANT(std::streamsize, streamsize_max =
      72             :             boost::integer_traits<std::streamsize>::const_max
      73             :         );
      74             : 
      75             :     BOOST_STATIC_CONSTANT(unsigned int, precision_dec = limits::digits10 + 1U);
      76             : 
      77             :     BOOST_STATIC_ASSERT(!is_specialized_dec ||
      78             :             precision_dec <= streamsize_max + 0UL
      79             :         );
      80             : 
      81             :     BOOST_STATIC_CONSTANT(unsigned long, precision_bin =
      82             :             2UL + limits::digits * 30103UL / 100000UL
      83             :         );
      84             : 
      85             :     BOOST_STATIC_ASSERT(!is_specialized_bin ||
      86             :             (limits::digits + 0UL < ULONG_MAX / 30103UL &&
      87             :             precision_bin > limits::digits10 + 0UL &&
      88             :             precision_bin <= streamsize_max + 0UL)
      89             :         );
      90             : 
      91             :     BOOST_STATIC_CONSTANT(std::streamsize, value =
      92             :             is_specialized_bin ? precision_bin
      93             :                                : is_specialized_dec ? precision_dec : 6
      94             :         );
      95             : };
      96             : #endif
      97             : 
      98             : template<class T>
      99           0 : inline std::streamsize lcast_get_precision(T* = 0)
     100             : {
     101             : #ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION
     102             :     return lcast_precision<T>::value;
     103             : #else // Follow lcast_precision algorithm at run-time:
     104             : 
     105             : #ifdef BOOST_NO_IS_ABSTRACT
     106             :     typedef std::numeric_limits<T> limits; // No fix for SF:1358600.
     107             : #else
     108             :     typedef BOOST_DEDUCED_TYPENAME boost::conditional<
     109             :         boost::is_abstract<T>::value
     110             :       , std::numeric_limits<lcast_abstract_stub>
     111             :       , std::numeric_limits<T>
     112             :       >::type limits;
     113             : #endif
     114             : 
     115             :     bool const use_default_precision =
     116             :         !limits::is_specialized || limits::is_exact;
     117             : 
     118             :     if(!use_default_precision)
     119             :     { // Includes all built-in floating-point types, float, double ...
     120             :       // and UDT types for which digits (significand bits) is defined (not zero)
     121             : 
     122             :         bool const is_specialized_bin =
     123             :             limits::radix == 2 && limits::digits > 0;
     124             :         bool const is_specialized_dec =
     125             :             limits::radix == 10 && limits::digits10 > 0;
     126             :         std::streamsize const streamsize_max =
     127             :             (boost::integer_traits<std::streamsize>::max)();
     128             :         (void)streamsize_max;
     129             : 
     130             :         if(is_specialized_bin)
     131             :         { // Floating-point types with
     132             :           // limits::digits defined by the specialization.
     133             : 
     134             :             unsigned long const digits = limits::digits;
     135             :             unsigned long const precision = 2UL + digits * 30103UL / 100000UL;
     136             :             // unsigned long is selected because it is at least 32-bits
     137             :             // and thus ULONG_MAX / 30103UL is big enough for all types.
     138             :             BOOST_ASSERT(
     139             :                     digits < ULONG_MAX / 30103UL &&
     140             :                     precision > limits::digits10 + 0UL &&
     141             :                     precision <= streamsize_max + 0UL
     142             :                 );
     143             :             return precision;
     144             :         }
     145             :         else if(is_specialized_dec)
     146             :         {   // Decimal Floating-point type, most likely a User Defined Type
     147             :             // rather than a real floating-point hardware type.
     148             :             unsigned int const precision = limits::digits10 + 1U;
     149             :             BOOST_ASSERT(precision <= streamsize_max + 0UL);
     150             :             return precision;
     151             :         }
     152             :     }
     153             : 
     154             :     // Integral type (for which precision has no effect)
     155             :     // or type T for which limits is NOT specialized,
     156             :     // so assume stream precision remains the default 6 decimal digits.
     157             :     // Warning: if your User-defined Floating-point type T is NOT specialized,
     158             :     // then you may lose accuracy by only using 6 decimal digits.
     159             :     // To avoid this, you need to specialize T with either
     160             :     // radix == 2 and digits == the number of significand bits,
     161             :     // OR
     162             :     // radix = 10 and digits10 == the number of decimal digits.
     163             : 
     164             :     return 6;
     165             : #endif
     166             : }
     167             : 
     168             : template<class T>
     169             : inline void lcast_set_precision(std::ios_base& stream, T*)
     170             : {
     171             :     stream.precision(lcast_get_precision<T>());
     172             : }
     173             : 
     174             : template<class Source, class Target>
     175             : inline void lcast_set_precision(std::ios_base& stream, Source*, Target*)
     176             : {
     177             :     std::streamsize const s = lcast_get_precision(static_cast<Source*>(0));
     178             :     std::streamsize const t = lcast_get_precision(static_cast<Target*>(0));
     179             :     stream.precision(s > t ? s : t);
     180             : }
     181             : 
     182             : }}
     183             : 
     184             : #endif //  BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
     185             :