libstdc++-v3/include/ext/numeric_traits.h

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2007-2022 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the terms
   7 // of the GNU General Public License as published by the Free Software
   8 // Foundation; either version 3, or (at your option) any later
   9 // version.
  10
  11 // This library is distributed in the hope that it will be useful, but
  12 // WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 // General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file ext/numeric_traits.h
  26  *  This file is a GNU extension to the Standard C++ Library.
  27  */
  28
  29 #ifndef _EXT_NUMERIC_TRAITS
  30 #define _EXT_NUMERIC_TRAITS 1
  31
  32 #pragma GCC system_header
  33
  34 #include <bits/cpp_type_traits.h>
  35 #include <ext/type_traits.h>
  36
  37 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
  38 {
  39 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  40
  41   // Compile time constants for builtin types.
  42   // In C++98 std::numeric_limits member functions are not constant expressions
  43   // (that changed in C++11 with the addition of 'constexpr').
  44   // Even for C++11, this header is smaller than <limits> and can be used
  45   // when only is_signed, digits, min, or max values are needed for integers,
  46   // or is_signed, digits10, max_digits10, or max_exponent10 for floats.
  47
  48   // Unlike __is_integer (and std::is_integral) this trait is true for
  49   // non-standard built-in integer types such as __int128 and __int20.
  50   template<typename _Tp>
  51     struct __is_integer_nonstrict
  52     : public std::__is_integer<_Tp>
  53     {
  54       using std::__is_integer<_Tp>::__value;
  55
  56       // The number of bits in the value representation.
  57       enum { __width = __value ? sizeof(_Tp) * __CHAR_BIT__ : 0 };
  58     };
  59
  60   template<typename _Value>
  61     struct __numeric_traits_integer
  62     {
  63 #if __cplusplus >= 201103L
  64       static_assert(__is_integer_nonstrict<_Value>::__value,
  65                     "invalid specialization");
  66 #endif
  67
  68       // NB: these two are also available in std::numeric_limits as compile
  69       // time constants, but <limits> is big and we can avoid including it.
  70       static const bool __is_signed = (_Value)(-1) < 0;
  71       static const int __digits
  72         = __is_integer_nonstrict<_Value>::__width - __is_signed;
  73
  74       // The initializers must be constants so that __max and __min are too.
  75       static const _Value __max = __is_signed
  76         ? (((((_Value)1 << (__digits - 1)) - 1) << 1) + 1)
  77         : ~(_Value)0;
  78       static const _Value __min = __is_signed ? -__max - 1 : (_Value)0;
  79     };
  80
  81   template<typename _Value>
  82     const _Value __numeric_traits_integer<_Value>::__min;
  83
  84   template<typename _Value>
  85     const _Value __numeric_traits_integer<_Value>::__max;
  86
  87   template<typename _Value>
  88     const bool __numeric_traits_integer<_Value>::__is_signed;
  89
  90   template<typename _Value>
  91     const int __numeric_traits_integer<_Value>::__digits;
  92
  93   // Enable __numeric_traits_integer for types where the __is_integer_nonstrict
  94   // primary template doesn't give the right answer.
  95 #define _GLIBCXX_INT_N_TRAITS(T, WIDTH)                 \
  96   __extension__                                         \
  97   template<> struct __is_integer_nonstrict<T>           \
  98   {                                                     \
  99     enum { __value = 1 };                               \
 100     typedef std::__true_type __type;                    \
 101     enum { __width = WIDTH };                           \
 102   };                                                    \
 103   __extension__                                         \
 104   template<> struct __is_integer_nonstrict<unsigned T>  \
 105   {                                                     \
 106     enum { __value = 1 };                               \
 107     typedef std::__true_type __type;                    \
 108     enum { __width = WIDTH };                           \
 109   };
 110
 111   // We need to specify the width for some __intNN types because they
 112   // have padding bits, e.g. the object representation of __int20 has 32 bits,
 113   // but its width (number of bits in the value representation) is only 20.
 114 #if defined __GLIBCXX_TYPE_INT_N_0 && __GLIBCXX_BITSIZE_INT_N_0 % __CHAR_BIT__
 115   _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_0, __GLIBCXX_BITSIZE_INT_N_0)
 116 #endif
 117 #if defined __GLIBCXX_TYPE_INT_N_1 && __GLIBCXX_BITSIZE_INT_N_1 % __CHAR_BIT__
 118   _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_1, __GLIBCXX_BITSIZE_INT_N_1)
 119 #endif
 120 #if defined __GLIBCXX_TYPE_INT_N_2 && __GLIBCXX_BITSIZE_INT_N_2 % __CHAR_BIT__
 121   _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_2, __GLIBCXX_BITSIZE_INT_N_2)
 122 #endif
 123 #if defined __GLIBCXX_TYPE_INT_N_3 && __GLIBCXX_BITSIZE_INT_N_3 % __CHAR_BIT__
 124   _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_3, __GLIBCXX_BITSIZE_INT_N_3)
 125 #endif
 126
 127 #if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
 128   // In strict modes __is_integer<__int128> is false,
 129   // but we still want to define __numeric_traits_integer<__int128>.
 130   _GLIBCXX_INT_N_TRAITS(__int128, 128)
 131 #endif
 132
 133 #undef _GLIBCXX_INT_N_TRAITS
 134
 135 #if __cplusplus >= 201103L
 136   /// Convenience alias for __numeric_traits<integer-type>.
 137   template<typename _Tp>
 138     using __int_traits = __numeric_traits_integer<_Tp>;
 139 #endif
 140
 141 #define __glibcxx_floating(_Tp, _Fval, _Dval, _LDval) \
 142   (std::__are_same<_Tp, float>::__value ? _Fval \
 143    : std::__are_same<_Tp, double>::__value ? _Dval : _LDval)
 144
 145 #define __glibcxx_max_digits10(_Tp) \
 146   (2 + __glibcxx_floating(_Tp, __FLT_MANT_DIG__, __DBL_MANT_DIG__, \
 147                           __LDBL_MANT_DIG__) * 643L / 2136)
 148
 149 #define __glibcxx_digits10(_Tp) \
 150   __glibcxx_floating(_Tp, __FLT_DIG__, __DBL_DIG__, __LDBL_DIG__)
 151
 152 #define __glibcxx_max_exponent10(_Tp) \
 153   __glibcxx_floating(_Tp, __FLT_MAX_10_EXP__, __DBL_MAX_10_EXP__, \
 154                      __LDBL_MAX_10_EXP__)
 155
 156   // N.B. this only supports float, double and long double (no __float128 etc.)
 157   template<typename _Value>
 158     struct __numeric_traits_floating
 159     {
 160       // Only floating point types. See N1822.
 161       static const int __max_digits10 = __glibcxx_max_digits10(_Value);
 162
 163       // See above comment...
 164       static const bool __is_signed = true;
 165       static const int __digits10 = __glibcxx_digits10(_Value);
 166       static const int __max_exponent10 = __glibcxx_max_exponent10(_Value);
 167     };
 168
 169   template<typename _Value>
 170     const int __numeric_traits_floating<_Value>::__max_digits10;
 171
 172   template<typename _Value>
 173     const bool __numeric_traits_floating<_Value>::__is_signed;
 174
 175   template<typename _Value>
 176     const int __numeric_traits_floating<_Value>::__digits10;
 177
 178   template<typename _Value>
 179     const int __numeric_traits_floating<_Value>::__max_exponent10;
 180
 181 #undef __glibcxx_floating
 182 #undef __glibcxx_max_digits10
 183 #undef __glibcxx_digits10
 184 #undef __glibcxx_max_exponent10
 185
 186   template<typename _Value>
 187     struct __numeric_traits
 188     : public __numeric_traits_integer<_Value>
 189     { };
 190
 191   template<>
 192     struct __numeric_traits<float>
 193     : public __numeric_traits_floating<float>
 194     { };
 195
 196   template<>
 197     struct __numeric_traits<double>
 198     : public __numeric_traits_floating<double>
 199     { };
 200
 201   template<>
 202     struct __numeric_traits<long double>
 203     : public __numeric_traits_floating<long double>
 204     { };
 205
 206 #ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
 207 # if defined __LONG_DOUBLE_IEEE128__
 208   // long double is __ieee128, define traits for __ibm128
 209   template<>
 210     struct __numeric_traits_floating<__ibm128>
 211     {
 212       static const int __max_digits10 = 33;
 213       static const bool __is_signed = true;
 214       static const int __digits10 = 31;
 215       static const int __max_exponent10 = 308;
 216     };
 217   template<>
 218     struct __numeric_traits<__ibm128>
 219     : public __numeric_traits_floating<__ibm128>
 220     { };
 221 # elif defined __LONG_DOUBLE_IBM128__
 222   // long double is __ibm128, define traits for __ieee128
 223   template<>
 224     struct __numeric_traits_floating<__ieee128>
 225     {
 226       static const int __max_digits10 = 36;
 227       static const bool __is_signed = true;
 228       static const int __digits10 = 33;
 229       static const int __max_exponent10 = 4932;
 230     };
 231   template<>
 232     struct __numeric_traits<__ieee128>
 233     : public __numeric_traits_floating<__ieee128>
 234     { };
 235 # endif
 236 #endif
 237
 238 _GLIBCXX_END_NAMESPACE_VERSION
 239 } // namespace
 240
 241 #endif