libstdc++
bit
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1 // <bit> -*- C++ -*-
2 
3 // Copyright (C) 2018-2021 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
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU 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 include/bit
26  * This is a Standard C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_BIT
30 #define _GLIBCXX_BIT 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus >= 201402L
35 
36 #include <type_traits>
37 
38 #if _GLIBCXX_HOSTED
39 # include <ext/numeric_traits.h>
40 #else
41 # include <limits>
42 /// @cond undocumented
43 namespace __gnu_cxx
44 {
45  template<typename _Tp>
46  struct __int_traits
47  {
48  static constexpr int __digits = std::numeric_limits<_Tp>::digits;
49  static constexpr _Tp __max = std::numeric_limits<_Tp>::max();
50  };
51 }
52 /// @endcond
53 #endif
54 
55 namespace std _GLIBCXX_VISIBILITY(default)
56 {
57 _GLIBCXX_BEGIN_NAMESPACE_VERSION
58 
59  /**
60  * @defgroup bit_manip Bit manipulation
61  * @ingroup numerics
62  *
63  * Utilities for examining and manipulating individual bits.
64  *
65  * @{
66  */
67 
68 #if __cplusplus > 201703l && __has_builtin(__builtin_bit_cast)
69 #define __cpp_lib_bit_cast 201806L
70 
71  /// Create a value of type `To` from the bits of `from`.
72  template<typename _To, typename _From>
73  [[nodiscard]]
74  constexpr _To
75  bit_cast(const _From& __from) noexcept
76 #ifdef __cpp_concepts
77  requires (sizeof(_To) == sizeof(_From))
78  && __is_trivially_copyable(_To) && __is_trivially_copyable(_From)
79 #endif
80  {
81  return __builtin_bit_cast(_To, __from);
82  }
83 #endif
84 
85  /// @cond undoc
86 
87  template<typename _Tp>
88  constexpr _Tp
89  __rotl(_Tp __x, int __s) noexcept
90  {
91  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
92  if _GLIBCXX17_CONSTEXPR ((_Nd & (_Nd - 1)) == 0)
93  {
94  // Variant for power of two _Nd which the compiler can
95  // easily pattern match.
96  constexpr unsigned __uNd = _Nd;
97  const unsigned __r = __s;
98  return (__x << (__r % __uNd)) | (__x >> ((-__r) % __uNd));
99  }
100  const int __r = __s % _Nd;
101  if (__r == 0)
102  return __x;
103  else if (__r > 0)
104  return (__x << __r) | (__x >> ((_Nd - __r) % _Nd));
105  else
106  return (__x >> -__r) | (__x << ((_Nd + __r) % _Nd)); // rotr(x, -r)
107  }
108 
109  template<typename _Tp>
110  constexpr _Tp
111  __rotr(_Tp __x, int __s) noexcept
112  {
113  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
114  if _GLIBCXX17_CONSTEXPR ((_Nd & (_Nd - 1)) == 0)
115  {
116  // Variant for power of two _Nd which the compiler can
117  // easily pattern match.
118  constexpr unsigned __uNd = _Nd;
119  const unsigned __r = __s;
120  return (__x >> (__r % __uNd)) | (__x << ((-__r) % __uNd));
121  }
122  const int __r = __s % _Nd;
123  if (__r == 0)
124  return __x;
125  else if (__r > 0)
126  return (__x >> __r) | (__x << ((_Nd - __r) % _Nd));
127  else
128  return (__x << -__r) | (__x >> ((_Nd + __r) % _Nd)); // rotl(x, -r)
129  }
130 
131  template<typename _Tp>
132  constexpr int
133  __countl_zero(_Tp __x) noexcept
134  {
135  using __gnu_cxx::__int_traits;
136  constexpr auto _Nd = __int_traits<_Tp>::__digits;
137 
138  if (__x == 0)
139  return _Nd;
140 
141  constexpr auto _Nd_ull = __int_traits<unsigned long long>::__digits;
142  constexpr auto _Nd_ul = __int_traits<unsigned long>::__digits;
143  constexpr auto _Nd_u = __int_traits<unsigned>::__digits;
144 
145  if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
146  {
147  constexpr int __diff = _Nd_u - _Nd;
148  return __builtin_clz(__x) - __diff;
149  }
150  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
151  {
152  constexpr int __diff = _Nd_ul - _Nd;
153  return __builtin_clzl(__x) - __diff;
154  }
155  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
156  {
157  constexpr int __diff = _Nd_ull - _Nd;
158  return __builtin_clzll(__x) - __diff;
159  }
160  else // (_Nd > _Nd_ull)
161  {
162  static_assert(_Nd <= (2 * _Nd_ull),
163  "Maximum supported integer size is 128-bit");
164 
165  unsigned long long __high = __x >> _Nd_ull;
166  if (__high != 0)
167  {
168  constexpr int __diff = (2 * _Nd_ull) - _Nd;
169  return __builtin_clzll(__high) - __diff;
170  }
171  constexpr auto __max_ull = __int_traits<unsigned long long>::__max;
172  unsigned long long __low = __x & __max_ull;
173  return (_Nd - _Nd_ull) + __builtin_clzll(__low);
174  }
175  }
176 
177  template<typename _Tp>
178  constexpr int
179  __countl_one(_Tp __x) noexcept
180  {
181  return std::__countl_zero<_Tp>((_Tp)~__x);
182  }
183 
184  template<typename _Tp>
185  constexpr int
186  __countr_zero(_Tp __x) noexcept
187  {
188  using __gnu_cxx::__int_traits;
189  constexpr auto _Nd = __int_traits<_Tp>::__digits;
190 
191  if (__x == 0)
192  return _Nd;
193 
194  constexpr auto _Nd_ull = __int_traits<unsigned long long>::__digits;
195  constexpr auto _Nd_ul = __int_traits<unsigned long>::__digits;
196  constexpr auto _Nd_u = __int_traits<unsigned>::__digits;
197 
198  if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
199  return __builtin_ctz(__x);
200  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
201  return __builtin_ctzl(__x);
202  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
203  return __builtin_ctzll(__x);
204  else // (_Nd > _Nd_ull)
205  {
206  static_assert(_Nd <= (2 * _Nd_ull),
207  "Maximum supported integer size is 128-bit");
208 
209  constexpr auto __max_ull = __int_traits<unsigned long long>::__max;
210  unsigned long long __low = __x & __max_ull;
211  if (__low != 0)
212  return __builtin_ctzll(__low);
213  unsigned long long __high = __x >> _Nd_ull;
214  return __builtin_ctzll(__high) + _Nd_ull;
215  }
216  }
217 
218  template<typename _Tp>
219  constexpr int
220  __countr_one(_Tp __x) noexcept
221  {
222  return std::__countr_zero((_Tp)~__x);
223  }
224 
225  template<typename _Tp>
226  constexpr int
227  __popcount(_Tp __x) noexcept
228  {
229  using __gnu_cxx::__int_traits;
230  constexpr auto _Nd = __int_traits<_Tp>::__digits;
231 
232  constexpr auto _Nd_ull = __int_traits<unsigned long long>::__digits;
233  constexpr auto _Nd_ul = __int_traits<unsigned long>::__digits;
234  constexpr auto _Nd_u = __int_traits<unsigned>::__digits;
235 
236  if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
237  return __builtin_popcount(__x);
238  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
239  return __builtin_popcountl(__x);
240  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
241  return __builtin_popcountll(__x);
242  else // (_Nd > _Nd_ull)
243  {
244  static_assert(_Nd <= (2 * _Nd_ull),
245  "Maximum supported integer size is 128-bit");
246 
247  constexpr auto __max_ull = __int_traits<unsigned long long>::__max;
248  unsigned long long __low = __x & __max_ull;
249  unsigned long long __high = __x >> _Nd_ull;
250  return __builtin_popcountll(__low) + __builtin_popcountll(__high);
251  }
252  }
253 
254  template<typename _Tp>
255  constexpr bool
256  __has_single_bit(_Tp __x) noexcept
257  { return std::__popcount(__x) == 1; }
258 
259  template<typename _Tp>
260  constexpr _Tp
261  __bit_ceil(_Tp __x) noexcept
262  {
263  using __gnu_cxx::__int_traits;
264  constexpr auto _Nd = __int_traits<_Tp>::__digits;
265  if (__x == 0 || __x == 1)
266  return 1;
267  auto __shift_exponent = _Nd - std::__countl_zero((_Tp)(__x - 1u));
268  // If the shift exponent equals _Nd then the correct result is not
269  // representable as a value of _Tp, and so the result is undefined.
270  // Want that undefined behaviour to be detected in constant expressions,
271  // by UBSan, and by debug assertions.
272 #ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
273  if (!__builtin_is_constant_evaluated())
274  {
275  __glibcxx_assert( __shift_exponent != __int_traits<_Tp>::__digits );
276  }
277 #endif
278  using __promoted_type = decltype(__x << 1);
279  if _GLIBCXX17_CONSTEXPR (!is_same<__promoted_type, _Tp>::value)
280  {
281  // If __x undergoes integral promotion then shifting by _Nd is
282  // not undefined. In order to make the shift undefined, so that
283  // it is diagnosed in constant expressions and by UBsan, we also
284  // need to "promote" the shift exponent to be too large for the
285  // promoted type.
286  const int __extra_exp = sizeof(__promoted_type) / sizeof(_Tp) / 2;
287  __shift_exponent |= (__shift_exponent & _Nd) << __extra_exp;
288  }
289  return (_Tp)1u << __shift_exponent;
290  }
291 
292  template<typename _Tp>
293  constexpr _Tp
294  __bit_floor(_Tp __x) noexcept
295  {
296  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
297  if (__x == 0)
298  return 0;
299  return (_Tp)1u << (_Nd - std::__countl_zero((_Tp)(__x >> 1)));
300  }
301 
302  template<typename _Tp>
303  constexpr _Tp
304  __bit_width(_Tp __x) noexcept
305  {
306  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
307  return _Nd - std::__countl_zero(__x);
308  }
309 
310  /// @endcond
311 
312 #if __cplusplus > 201703L
313 
314 #define __cpp_lib_bitops 201907L
315 
316  /// @cond undoc
317  template<typename _Tp, typename _Up = _Tp>
318  using _If_is_unsigned_integer
319  = enable_if_t<__is_unsigned_integer<_Tp>::value, _Up>;
320  /// @endcond
321 
322  // [bit.rot], rotating
323 
324  /// Rotate `x` to the left by `s` bits.
325  template<typename _Tp>
326  [[nodiscard]] constexpr _If_is_unsigned_integer<_Tp>
327  rotl(_Tp __x, int __s) noexcept
328  { return std::__rotl(__x, __s); }
329 
330  /// Rotate `x` to the right by `s` bits.
331  template<typename _Tp>
332  [[nodiscard]] constexpr _If_is_unsigned_integer<_Tp>
333  rotr(_Tp __x, int __s) noexcept
334  { return std::__rotr(__x, __s); }
335 
336  // [bit.count], counting
337 
338  /// The number of contiguous zero bits, starting from the highest bit.
339  template<typename _Tp>
340  constexpr _If_is_unsigned_integer<_Tp, int>
341  countl_zero(_Tp __x) noexcept
342  { return std::__countl_zero(__x); }
343 
344  /// The number of contiguous one bits, starting from the highest bit.
345  template<typename _Tp>
346  constexpr _If_is_unsigned_integer<_Tp, int>
347  countl_one(_Tp __x) noexcept
348  { return std::__countl_one(__x); }
349 
350  /// The number of contiguous zero bits, starting from the lowest bit.
351  template<typename _Tp>
352  constexpr _If_is_unsigned_integer<_Tp, int>
353  countr_zero(_Tp __x) noexcept
354  { return std::__countr_zero(__x); }
355 
356  /// The number of contiguous one bits, starting from the lowest bit.
357  template<typename _Tp>
358  constexpr _If_is_unsigned_integer<_Tp, int>
359  countr_one(_Tp __x) noexcept
360  { return std::__countr_one(__x); }
361 
362  /// The number of bits set in `x`.
363  template<typename _Tp>
364  constexpr _If_is_unsigned_integer<_Tp, int>
365  popcount(_Tp __x) noexcept
366  { return std::__popcount(__x); }
367 
368  // [bit.pow.two], integral powers of 2
369 
370 #define __cpp_lib_int_pow2 202002L
371 
372  /// True if `x` is a power of two, false otherwise.
373  template<typename _Tp>
374  constexpr _If_is_unsigned_integer<_Tp, bool>
375  has_single_bit(_Tp __x) noexcept
376  { return std::__has_single_bit(__x); }
377 
378  /// The smallest power-of-two not less than `x`.
379  template<typename _Tp>
380  constexpr _If_is_unsigned_integer<_Tp>
381  bit_ceil(_Tp __x) noexcept
382  { return std::__bit_ceil(__x); }
383 
384  /// The largest power-of-two not greater than `x`.
385  template<typename _Tp>
386  constexpr _If_is_unsigned_integer<_Tp>
387  bit_floor(_Tp __x) noexcept
388  { return std::__bit_floor(__x); }
389 
390  /// The smallest integer greater than the base-2 logarithm of `x`.
391  template<typename _Tp>
392  constexpr _If_is_unsigned_integer<_Tp>
393  bit_width(_Tp __x) noexcept
394  { return std::__bit_width(__x); }
395 
396 #define __cpp_lib_endian 201907L
397 
398  /// Byte order
399  enum class endian
400  {
401  little = __ORDER_LITTLE_ENDIAN__,
402  big = __ORDER_BIG_ENDIAN__,
403  native = __BYTE_ORDER__
404  };
405 #endif // C++2a
406 
407  /// @}
408 
409 _GLIBCXX_END_NAMESPACE_VERSION
410 } // namespace std
411 
412 #endif // C++14
413 #endif // _GLIBCXX_BIT