libstdc++
ext/numeric_traits.h
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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  template<> struct __is_integer_nonstrict<T> \
97  { \
98  enum { __value = 1 }; \
99  typedef std::__true_type __type; \
100  enum { __width = WIDTH }; \
101  }; \
102  template<> struct __is_integer_nonstrict<unsigned T> \
103  { \
104  enum { __value = 1 }; \
105  typedef std::__true_type __type; \
106  enum { __width = WIDTH }; \
107  };
108 
109  // We need to specify the width for some __intNN types because they
110  // have padding bits, e.g. the object representation of __int20 has 32 bits,
111  // but its width (number of bits in the value representation) is only 20.
112 #if defined __GLIBCXX_TYPE_INT_N_0 && __GLIBCXX_BITSIZE_INT_N_0 % __CHAR_BIT__
113  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_0, __GLIBCXX_BITSIZE_INT_N_0)
114 #endif
115 #if defined __GLIBCXX_TYPE_INT_N_1 && __GLIBCXX_BITSIZE_INT_N_1 % __CHAR_BIT__
116  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_1, __GLIBCXX_BITSIZE_INT_N_1)
117 #endif
118 #if defined __GLIBCXX_TYPE_INT_N_2 && __GLIBCXX_BITSIZE_INT_N_2 % __CHAR_BIT__
119  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_2, __GLIBCXX_BITSIZE_INT_N_2)
120 #endif
121 #if defined __GLIBCXX_TYPE_INT_N_3 && __GLIBCXX_BITSIZE_INT_N_3 % __CHAR_BIT__
122  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_3, __GLIBCXX_BITSIZE_INT_N_3)
123 #endif
124 
125 #if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
126  // In strict modes __is_integer<__int128> is false,
127  // but we still want to define __numeric_traits_integer<__int128>.
128  _GLIBCXX_INT_N_TRAITS(__int128, 128)
129 #endif
130 
131 #undef _GLIBCXX_INT_N_TRAITS
132 
133 #if __cplusplus >= 201103L
134  /// Convenience alias for __numeric_traits<integer-type>.
135  template<typename _Tp>
136  using __int_traits = __numeric_traits_integer<_Tp>;
137 #endif
138 
139 #define __glibcxx_floating(_Tp, _Fval, _Dval, _LDval) \
140  (std::__are_same<_Tp, float>::__value ? _Fval \
141  : std::__are_same<_Tp, double>::__value ? _Dval : _LDval)
142 
143 #define __glibcxx_max_digits10(_Tp) \
144  (2 + __glibcxx_floating(_Tp, __FLT_MANT_DIG__, __DBL_MANT_DIG__, \
145  __LDBL_MANT_DIG__) * 643L / 2136)
146 
147 #define __glibcxx_digits10(_Tp) \
148  __glibcxx_floating(_Tp, __FLT_DIG__, __DBL_DIG__, __LDBL_DIG__)
149 
150 #define __glibcxx_max_exponent10(_Tp) \
151  __glibcxx_floating(_Tp, __FLT_MAX_10_EXP__, __DBL_MAX_10_EXP__, \
152  __LDBL_MAX_10_EXP__)
153 
154  // N.B. this only supports float, double and long double (no __float128 etc.)
155  template<typename _Value>
156  struct __numeric_traits_floating
157  {
158  // Only floating point types. See N1822.
159  static const int __max_digits10 = __glibcxx_max_digits10(_Value);
160 
161  // See above comment...
162  static const bool __is_signed = true;
163  static const int __digits10 = __glibcxx_digits10(_Value);
164  static const int __max_exponent10 = __glibcxx_max_exponent10(_Value);
165  };
166 
167  template<typename _Value>
168  const int __numeric_traits_floating<_Value>::__max_digits10;
169 
170  template<typename _Value>
171  const bool __numeric_traits_floating<_Value>::__is_signed;
172 
173  template<typename _Value>
174  const int __numeric_traits_floating<_Value>::__digits10;
175 
176  template<typename _Value>
177  const int __numeric_traits_floating<_Value>::__max_exponent10;
178 
179 #undef __glibcxx_floating
180 #undef __glibcxx_max_digits10
181 #undef __glibcxx_digits10
182 #undef __glibcxx_max_exponent10
183 
184  template<typename _Value>
185  struct __numeric_traits
186  : public __numeric_traits_integer<_Value>
187  { };
188 
189  template<>
190  struct __numeric_traits<float>
191  : public __numeric_traits_floating<float>
192  { };
193 
194  template<>
195  struct __numeric_traits<double>
196  : public __numeric_traits_floating<double>
197  { };
198 
199  template<>
200  struct __numeric_traits<long double>
201  : public __numeric_traits_floating<long double>
202  { };
203 
204 #ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
205 # if defined __LONG_DOUBLE_IEEE128__
206  // long double is __ieee128, define traits for __ibm128
207  template<>
208  struct __numeric_traits_floating<__ibm128>
209  {
210  static const int __max_digits10 = 33;
211  static const bool __is_signed = true;
212  static const int __digits10 = 31;
213  static const int __max_exponent10 = 308;
214  };
215  template<>
216  struct __numeric_traits<__ibm128>
217  : public __numeric_traits_floating<__ibm128>
218  { };
219 # elif defined __LONG_DOUBLE_IBM128__
220  // long double is __ibm128, define traits for __ieee128
221  template<>
222  struct __numeric_traits_floating<__ieee128>
223  {
224  static const int __max_digits10 = 36;
225  static const bool __is_signed = true;
226  static const int __digits10 = 33;
227  static const int __max_exponent10 = 4932;
228  };
229  template<>
230  struct __numeric_traits<__ieee128>
231  : public __numeric_traits_floating<__ieee128>
232  { };
233 # endif
234 #endif
235 
236 _GLIBCXX_END_NAMESPACE_VERSION
237 } // namespace
238 
239 #endif
GNU extensions for public use.
__numeric_traits_integer< _Tp > __int_traits
Convenience alias for __numeric_traits<integer-type>.