ceph/src/boost/boost/detail/lcast_precision.hpp

   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/mpl/if.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::mpl::if_<
  51         boost::is_abstract<T>
  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 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::mpl::if_<
 109         boost::is_abstract<T>
 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