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 #ifdef _GLIBCXX_SYSHDR
33 #pragma GCC system_header
34 #endif
35 
36 #include <bits/cpp_type_traits.h>
37 #include <ext/type_traits.h>
38 
39 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
40 {
41 _GLIBCXX_BEGIN_NAMESPACE_VERSION
42 
43  // Compile time constants for builtin types.
44  // In C++98 std::numeric_limits member functions are not constant expressions
45  // (that changed in C++11 with the addition of 'constexpr').
46  // Even for C++11, this header is smaller than <limits> and can be used
47  // when only is_signed, digits, min, or max values are needed for integers,
48  // or is_signed, digits10, max_digits10, or max_exponent10 for floats.
49 
50  // Unlike __is_integer (and std::is_integral) this trait is true for
51  // non-standard built-in integer types such as __int128 and __int20.
52  template<typename _Tp>
53  struct __is_integer_nonstrict
54  : public std::__is_integer<_Tp>
55  {
56  using std::__is_integer<_Tp>::__value;
57 
58  // The number of bits in the value representation.
59  enum { __width = __value ? sizeof(_Tp) * __CHAR_BIT__ : 0 };
60  };
61 
62  template<typename _Value>
63  struct __numeric_traits_integer
64  {
65 #if __cplusplus >= 201103L
66  static_assert(__is_integer_nonstrict<_Value>::__value,
67  "invalid specialization");
68 #endif
69 
70  // NB: these two are also available in std::numeric_limits as compile
71  // time constants, but <limits> is big and we can avoid including it.
72  static const bool __is_signed = (_Value)(-1) < 0;
73  static const int __digits
74  = __is_integer_nonstrict<_Value>::__width - __is_signed;
75 
76  // The initializers must be constants so that __max and __min are too.
77  static const _Value __max = __is_signed
78  ? (((((_Value)1 << (__digits - 1)) - 1) << 1) + 1)
79  : ~(_Value)0;
80  static const _Value __min = __is_signed ? -__max - 1 : (_Value)0;
81  };
82 
83  template<typename _Value>
84  const _Value __numeric_traits_integer<_Value>::__min;
85 
86  template<typename _Value>
87  const _Value __numeric_traits_integer<_Value>::__max;
88 
89  template<typename _Value>
90  const bool __numeric_traits_integer<_Value>::__is_signed;
91 
92  template<typename _Value>
93  const int __numeric_traits_integer<_Value>::__digits;
94 
95  // Enable __numeric_traits_integer for types where the __is_integer_nonstrict
96  // primary template doesn't give the right answer.
97 #define _GLIBCXX_INT_N_TRAITS(T, WIDTH) \
98  __extension__ \
99  template<> struct __is_integer_nonstrict<T> \
100  { \
101  enum { __value = 1 }; \
102  typedef std::__true_type __type; \
103  enum { __width = WIDTH }; \
104  }; \
105  __extension__ \
106  template<> struct __is_integer_nonstrict<unsigned T> \
107  { \
108  enum { __value = 1 }; \
109  typedef std::__true_type __type; \
110  enum { __width = WIDTH }; \
111  };
112 
113  // We need to specify the width for some __intNN types because they
114  // have padding bits, e.g. the object representation of __int20 has 32 bits,
115  // but its width (number of bits in the value representation) is only 20.
116 #if defined __GLIBCXX_TYPE_INT_N_0 && __GLIBCXX_BITSIZE_INT_N_0 % __CHAR_BIT__
117  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_0, __GLIBCXX_BITSIZE_INT_N_0)
118 #endif
119 #if defined __GLIBCXX_TYPE_INT_N_1 && __GLIBCXX_BITSIZE_INT_N_1 % __CHAR_BIT__
120  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_1, __GLIBCXX_BITSIZE_INT_N_1)
121 #endif
122 #if defined __GLIBCXX_TYPE_INT_N_2 && __GLIBCXX_BITSIZE_INT_N_2 % __CHAR_BIT__
123  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_2, __GLIBCXX_BITSIZE_INT_N_2)
124 #endif
125 #if defined __GLIBCXX_TYPE_INT_N_3 && __GLIBCXX_BITSIZE_INT_N_3 % __CHAR_BIT__
126  _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_3, __GLIBCXX_BITSIZE_INT_N_3)
127 #endif
128 
129 #if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
130  // In strict modes __is_integer<__int128> is false,
131  // but we still want to define __numeric_traits_integer<__int128>.
132  _GLIBCXX_INT_N_TRAITS(__int128, 128)
133 #endif
134 
135 #undef _GLIBCXX_INT_N_TRAITS
136 
137 #if __cplusplus >= 201103L
138  /// Convenience alias for __numeric_traits<integer-type>.
139  template<typename _Tp>
140  using __int_traits = __numeric_traits_integer<_Tp>;
141 #endif
142 
143 #define __glibcxx_floating(_Tp, _Fval, _Dval, _LDval) \
144  (std::__are_same<_Tp, float>::__value ? _Fval \
145  : std::__are_same<_Tp, double>::__value ? _Dval : _LDval)
146 
147 #define __glibcxx_max_digits10(_Tp) \
148  (2 + __glibcxx_floating(_Tp, __FLT_MANT_DIG__, __DBL_MANT_DIG__, \
149  __LDBL_MANT_DIG__) * 643L / 2136)
150 
151 #define __glibcxx_digits10(_Tp) \
152  __glibcxx_floating(_Tp, __FLT_DIG__, __DBL_DIG__, __LDBL_DIG__)
153 
154 #define __glibcxx_max_exponent10(_Tp) \
155  __glibcxx_floating(_Tp, __FLT_MAX_10_EXP__, __DBL_MAX_10_EXP__, \
156  __LDBL_MAX_10_EXP__)
157 
158  // N.B. this only supports float, double and long double (no __float128 etc.)
159  template<typename _Value>
160  struct __numeric_traits_floating
161  {
162  // Only floating point types. See N1822.
163  static const int __max_digits10 = __glibcxx_max_digits10(_Value);
164 
165  // See above comment...
166  static const bool __is_signed = true;
167  static const int __digits10 = __glibcxx_digits10(_Value);
168  static const int __max_exponent10 = __glibcxx_max_exponent10(_Value);
169  };
170 
171  template<typename _Value>
172  const int __numeric_traits_floating<_Value>::__max_digits10;
173 
174  template<typename _Value>
175  const bool __numeric_traits_floating<_Value>::__is_signed;
176 
177  template<typename _Value>
178  const int __numeric_traits_floating<_Value>::__digits10;
179 
180  template<typename _Value>
181  const int __numeric_traits_floating<_Value>::__max_exponent10;
182 
183 #undef __glibcxx_floating
184 #undef __glibcxx_max_digits10
185 #undef __glibcxx_digits10
186 #undef __glibcxx_max_exponent10
187 
188  template<typename _Value>
189  struct __numeric_traits
190  : public __numeric_traits_integer<_Value>
191  { };
192 
193  template<>
194  struct __numeric_traits<float>
195  : public __numeric_traits_floating<float>
196  { };
197 
198  template<>
199  struct __numeric_traits<double>
200  : public __numeric_traits_floating<double>
201  { };
202 
203  template<>
204  struct __numeric_traits<long double>
205  : public __numeric_traits_floating<long double>
206  { };
207 
208 #ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
209 # if defined __LONG_DOUBLE_IEEE128__
210  // long double is __ieee128, define traits for __ibm128
211  template<>
212  struct __numeric_traits_floating<__ibm128>
213  {
214  static const int __max_digits10 = 33;
215  static const bool __is_signed = true;
216  static const int __digits10 = 31;
217  static const int __max_exponent10 = 308;
218  };
219  template<>
220  struct __numeric_traits<__ibm128>
221  : public __numeric_traits_floating<__ibm128>
222  { };
223 # elif defined __LONG_DOUBLE_IBM128__
224  // long double is __ibm128, define traits for __ieee128
225  template<>
226  struct __numeric_traits_floating<__ieee128>
227  {
228  static const int __max_digits10 = 36;
229  static const bool __is_signed = true;
230  static const int __digits10 = 33;
231  static const int __max_exponent10 = 4932;
232  };
233  template<>
234  struct __numeric_traits<__ieee128>
235  : public __numeric_traits_floating<__ieee128>
236  { };
237 # endif
238 #endif
239 
240 _GLIBCXX_END_NAMESPACE_VERSION
241 } // namespace
242 
243 #endif
GNU extensions for public use.
__numeric_traits_integer< _Tp > __int_traits
Convenience alias for __numeric_traits<integer-type>.