libstdc++
bit
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1 // <bit> -*- C++ -*-
2 
3 // Copyright (C) 2018-2025 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 #ifdef _GLIBCXX_SYSHDR
33 #pragma GCC system_header
34 #endif
35 
36 #if __cplusplus >= 201402L
37 
38 #include <concepts> // for std::integral
39 #include <type_traits>
40 
41 #if _GLIBCXX_HOSTED || __has_include(<ext/numeric_traits.h>)
42 # include <ext/numeric_traits.h>
43 #else
44 # include <limits>
45 /// @cond undocumented
46 namespace __gnu_cxx
47 {
48  template<typename _Tp>
49  struct __int_traits
50  {
51  static constexpr int __digits = std::numeric_limits<_Tp>::digits;
52  static constexpr _Tp __max = std::numeric_limits<_Tp>::max();
53  };
54 }
55 /// @endcond
56 #endif
57 
58 #define __glibcxx_want_bit_cast
59 #define __glibcxx_want_byteswap
60 #define __glibcxx_want_bitops
61 #define __glibcxx_want_int_pow2
62 #define __glibcxx_want_endian
63 #include <bits/version.h>
64 
65 namespace std _GLIBCXX_VISIBILITY(default)
66 {
67 _GLIBCXX_BEGIN_NAMESPACE_VERSION
68 
69  /**
70  * @defgroup bit_manip Bit manipulation
71  * @ingroup numerics
72  *
73  * Utilities for examining and manipulating individual bits.
74  *
75  * @{
76  */
77 
78 #ifdef __cpp_lib_bit_cast // C++ >= 20
79 
80  /// Create a value of type `To` from the bits of `from`.
81  /**
82  * @tparam _To A trivially-copyable type.
83  * @param __from A trivially-copyable object of the same size as `_To`.
84  * @return An object of type `_To`.
85  * @since C++20
86  */
87  template<typename _To, typename _From>
88  [[nodiscard]]
89  constexpr _To
90  bit_cast(const _From& __from) noexcept
91 #ifdef __cpp_concepts
92  requires (sizeof(_To) == sizeof(_From))
93  && is_trivially_copyable_v<_To> && is_trivially_copyable_v<_From>
94 #endif
95  {
96  return __builtin_bit_cast(_To, __from);
97  }
98 #endif // __cpp_lib_bit_cast
99 
100 #ifdef __cpp_lib_byteswap // C++ >= 23
101 
102  /// Reverse order of bytes in the object representation of `value`.
103  /**
104  * @tparam _Tp An integral type.
105  * @param __value An object of integer type.
106  * @return An object of the same type, with the bytes reversed.
107  * @since C++23
108  */
109  template<integral _Tp>
110  [[nodiscard]]
111  constexpr _Tp
112  byteswap(_Tp __value) noexcept
113  {
114  if constexpr (sizeof(_Tp) == 1)
115  return __value;
116 #if __cpp_if_consteval >= 202106L && __CHAR_BIT__ == 8
117  if !consteval
118  {
119  if constexpr (sizeof(_Tp) == 2)
120  return __builtin_bswap16(__value);
121  if constexpr (sizeof(_Tp) == 4)
122  return __builtin_bswap32(__value);
123  if constexpr (sizeof(_Tp) == 8)
124  return __builtin_bswap64(__value);
125  if constexpr (sizeof(_Tp) == 16)
126 #if __has_builtin(__builtin_bswap128)
127  return __builtin_bswap128(__value);
128 #else
129  return (__builtin_bswap64(__value >> 64)
130  | (static_cast<_Tp>(__builtin_bswap64(__value)) << 64));
131 #endif
132  }
133 #endif
134 
135  // Fallback implementation that handles even __int24 etc.
136  using _Up = typename __make_unsigned<__remove_cv_t<_Tp>>::__type;
137  size_t __diff = __CHAR_BIT__ * (sizeof(_Tp) - 1);
138  _Up __mask1 = static_cast<unsigned char>(~0);
139  _Up __mask2 = __mask1 << __diff;
140  _Up __val = __value;
141  for (size_t __i = 0; __i < sizeof(_Tp) / 2; ++__i)
142  {
143  _Up __byte1 = __val & __mask1;
144  _Up __byte2 = __val & __mask2;
145  __val = (__val ^ __byte1 ^ __byte2
146  ^ (__byte1 << __diff) ^ (__byte2 >> __diff));
147  __mask1 <<= __CHAR_BIT__;
148  __mask2 >>= __CHAR_BIT__;
149  __diff -= 2 * __CHAR_BIT__;
150  }
151  return __val;
152  }
153 #endif // __cpp_lib_byteswap
154 
155  /// @cond undocumented
156 
157  template<typename _Tp>
158  constexpr _Tp
159  __rotl(_Tp __x, int __s) noexcept
160  {
161  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
162  if _GLIBCXX17_CONSTEXPR ((_Nd & (_Nd - 1)) == 0)
163  {
164  // Variant for power of two _Nd which the compiler can
165  // easily pattern match.
166  constexpr unsigned __uNd = _Nd;
167  const unsigned __r = __s;
168  return (__x << (__r % __uNd)) | (__x >> ((-__r) % __uNd));
169  }
170  const int __r = __s % _Nd;
171  if (__r == 0)
172  return __x;
173  else if (__r > 0)
174  return (__x << __r) | (__x >> ((_Nd - __r) % _Nd));
175  else
176  return (__x >> -__r) | (__x << ((_Nd + __r) % _Nd)); // rotr(x, -r)
177  }
178 
179  template<typename _Tp>
180  constexpr _Tp
181  __rotr(_Tp __x, int __s) noexcept
182  {
183  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
184  if _GLIBCXX17_CONSTEXPR ((_Nd & (_Nd - 1)) == 0)
185  {
186  // Variant for power of two _Nd which the compiler can
187  // easily pattern match.
188  constexpr unsigned __uNd = _Nd;
189  const unsigned __r = __s;
190  return (__x >> (__r % __uNd)) | (__x << ((-__r) % __uNd));
191  }
192  const int __r = __s % _Nd;
193  if (__r == 0)
194  return __x;
195  else if (__r > 0)
196  return (__x >> __r) | (__x << ((_Nd - __r) % _Nd));
197  else
198  return (__x << -__r) | (__x >> ((_Nd + __r) % _Nd)); // rotl(x, -r)
199  }
200 
201  template<typename _Tp>
202  constexpr int
203  __countl_zero(_Tp __x) noexcept
204  {
205  using __gnu_cxx::__int_traits;
206  constexpr auto _Nd = __int_traits<_Tp>::__digits;
207 
208 #if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_clzg)
209  return __builtin_clzg(__x, _Nd);
210 #else
211  if (__x == 0)
212  return _Nd;
213 
214  constexpr auto _Nd_ull = __int_traits<unsigned long long>::__digits;
215  constexpr auto _Nd_ul = __int_traits<unsigned long>::__digits;
216  constexpr auto _Nd_u = __int_traits<unsigned>::__digits;
217 
218  if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
219  {
220  constexpr int __diff = _Nd_u - _Nd;
221  return __builtin_clz(__x) - __diff;
222  }
223  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
224  {
225  constexpr int __diff = _Nd_ul - _Nd;
226  return __builtin_clzl(__x) - __diff;
227  }
228  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
229  {
230  constexpr int __diff = _Nd_ull - _Nd;
231  return __builtin_clzll(__x) - __diff;
232  }
233  else // (_Nd > _Nd_ull)
234  {
235  static_assert(_Nd <= (2 * _Nd_ull),
236  "Maximum supported integer size is 128-bit");
237 
238  unsigned long long __high = __x >> _Nd_ull;
239  if (__high != 0)
240  {
241  constexpr int __diff = (2 * _Nd_ull) - _Nd;
242  return __builtin_clzll(__high) - __diff;
243  }
244  constexpr auto __max_ull = __int_traits<unsigned long long>::__max;
245  unsigned long long __low = __x & __max_ull;
246  return (_Nd - _Nd_ull) + __builtin_clzll(__low);
247  }
248 #endif
249  }
250 
251  template<typename _Tp>
252  constexpr int
253  __countl_one(_Tp __x) noexcept
254  {
255  return std::__countl_zero<_Tp>((_Tp)~__x);
256  }
257 
258  template<typename _Tp>
259  constexpr int
260  __countr_zero(_Tp __x) noexcept
261  {
262  using __gnu_cxx::__int_traits;
263  constexpr auto _Nd = __int_traits<_Tp>::__digits;
264 
265 #if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_ctzg)
266  return __builtin_ctzg(__x, _Nd);
267 #else
268  if (__x == 0)
269  return _Nd;
270 
271  constexpr auto _Nd_ull = __int_traits<unsigned long long>::__digits;
272  constexpr auto _Nd_ul = __int_traits<unsigned long>::__digits;
273  constexpr auto _Nd_u = __int_traits<unsigned>::__digits;
274 
275  if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
276  return __builtin_ctz(__x);
277  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
278  return __builtin_ctzl(__x);
279  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
280  return __builtin_ctzll(__x);
281  else // (_Nd > _Nd_ull)
282  {
283  static_assert(_Nd <= (2 * _Nd_ull),
284  "Maximum supported integer size is 128-bit");
285 
286  constexpr auto __max_ull = __int_traits<unsigned long long>::__max;
287  unsigned long long __low = __x & __max_ull;
288  if (__low != 0)
289  return __builtin_ctzll(__low);
290  unsigned long long __high = __x >> _Nd_ull;
291  return __builtin_ctzll(__high) + _Nd_ull;
292  }
293 #endif
294  }
295 
296  template<typename _Tp>
297  constexpr int
298  __countr_one(_Tp __x) noexcept
299  {
300  return std::__countr_zero((_Tp)~__x);
301  }
302 
303  template<typename _Tp>
304  constexpr int
305  __popcount(_Tp __x) noexcept
306  {
307 #if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_popcountg)
308  return __builtin_popcountg(__x);
309 #else
310  using __gnu_cxx::__int_traits;
311  constexpr auto _Nd = __int_traits<_Tp>::__digits;
312 
313  constexpr auto _Nd_ull = __int_traits<unsigned long long>::__digits;
314  constexpr auto _Nd_ul = __int_traits<unsigned long>::__digits;
315  constexpr auto _Nd_u = __int_traits<unsigned>::__digits;
316 
317  if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
318  return __builtin_popcount(__x);
319  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
320  return __builtin_popcountl(__x);
321  else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
322  return __builtin_popcountll(__x);
323  else // (_Nd > _Nd_ull)
324  {
325  static_assert(_Nd <= (2 * _Nd_ull),
326  "Maximum supported integer size is 128-bit");
327 
328  constexpr auto __max_ull = __int_traits<unsigned long long>::__max;
329  unsigned long long __low = __x & __max_ull;
330  unsigned long long __high = __x >> _Nd_ull;
331  return __builtin_popcountll(__low) + __builtin_popcountll(__high);
332  }
333 #endif
334  }
335 
336  template<typename _Tp>
337  constexpr bool
338  __has_single_bit(_Tp __x) noexcept
339  { return std::__popcount(__x) == 1; }
340 
341  template<typename _Tp>
342  constexpr _Tp
343  __bit_ceil(_Tp __x) noexcept
344  {
345  using __gnu_cxx::__int_traits;
346  constexpr auto _Nd = __int_traits<_Tp>::__digits;
347  if (__x == 0 || __x == 1)
348  return 1;
349  auto __shift_exponent = _Nd - std::__countl_zero((_Tp)(__x - 1u));
350  // If the shift exponent equals _Nd then the correct result is not
351  // representable as a value of _Tp, and so the result is undefined.
352  // Want that undefined behaviour to be detected in constant expressions,
353  // by UBSan, and by debug assertions.
354  if (!std::__is_constant_evaluated())
355  {
356  __glibcxx_assert( __shift_exponent != __int_traits<_Tp>::__digits );
357  }
358 
359  using __promoted_type = decltype(__x << 1);
360  if _GLIBCXX17_CONSTEXPR (!is_same<__promoted_type, _Tp>::value)
361  {
362  // If __x undergoes integral promotion then shifting by _Nd is
363  // not undefined. In order to make the shift undefined, so that
364  // it is diagnosed in constant expressions and by UBsan, we also
365  // need to "promote" the shift exponent to be too large for the
366  // promoted type.
367  const int __extra_exp = sizeof(__promoted_type) / sizeof(_Tp) / 2;
368  __shift_exponent |= (__shift_exponent & _Nd) << __extra_exp;
369  }
370  return (_Tp)1u << __shift_exponent;
371  }
372 
373  template<typename _Tp>
374  constexpr _Tp
375  __bit_floor(_Tp __x) noexcept
376  {
377  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
378  if (__x == 0)
379  return 0;
380  return (_Tp)1u << (_Nd - std::__countl_zero((_Tp)(__x >> 1)));
381  }
382 
383  template<typename _Tp>
384  constexpr int
385  __bit_width(_Tp __x) noexcept
386  {
387  constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
388  return _Nd - std::__countl_zero(__x);
389  }
390 
391  /// @endcond
392 
393 #ifdef __cpp_lib_bitops // C++ >= 20
394 
395  /// @cond undocumented
396  template<typename _Tp>
397  concept __unsigned_integer = __is_unsigned_integer<_Tp>::value;
398  /// @endcond
399 
400  // [bit.rot], rotating
401 
402  /// Rotate `x` to the left by `s` bits.
403  template<__unsigned_integer _Tp>
404  [[nodiscard]] constexpr _Tp
405  rotl(_Tp __x, int __s) noexcept
406  { return std::__rotl(__x, __s); }
407 
408  /// Rotate `x` to the right by `s` bits.
409  template<__unsigned_integer _Tp>
410  [[nodiscard]] constexpr _Tp
411  rotr(_Tp __x, int __s) noexcept
412  { return std::__rotr(__x, __s); }
413 
414  // [bit.count], counting
415 
416  /// The number of contiguous zero bits, starting from the highest bit.
417  template<__unsigned_integer _Tp>
418  constexpr int
419  countl_zero(_Tp __x) noexcept
420  { return std::__countl_zero(__x); }
421 
422  /// The number of contiguous one bits, starting from the highest bit.
423  template<__unsigned_integer _Tp>
424  constexpr int
425  countl_one(_Tp __x) noexcept
426  { return std::__countl_one(__x); }
427 
428  /// The number of contiguous zero bits, starting from the lowest bit.
429  template<__unsigned_integer _Tp>
430  constexpr int
431  countr_zero(_Tp __x) noexcept
432  { return std::__countr_zero(__x); }
433 
434  /// The number of contiguous one bits, starting from the lowest bit.
435  template<__unsigned_integer _Tp>
436  constexpr int
437  countr_one(_Tp __x) noexcept
438  { return std::__countr_one(__x); }
439 
440  /// The number of bits set in `x`.
441  template<__unsigned_integer _Tp>
442  constexpr int
443  popcount(_Tp __x) noexcept
444  { return std::__popcount(__x); }
445 #endif // __cpp_lib_bitops
446 
447 #ifdef __cpp_lib_int_pow2 // C++ >= 20
448  // [bit.pow.two], integral powers of 2
449 
450  /// True if `x` is a power of two, false otherwise.
451  template<__unsigned_integer _Tp>
452  constexpr bool
453  has_single_bit(_Tp __x) noexcept
454  { return std::__has_single_bit(__x); }
455 
456  /// The smallest power-of-two not less than `x`.
457  template<__unsigned_integer _Tp>
458  constexpr _Tp
459  bit_ceil(_Tp __x) noexcept
460  { return std::__bit_ceil(__x); }
461 
462  /// The largest power-of-two not greater than `x`.
463  template<__unsigned_integer _Tp>
464  constexpr _Tp
465  bit_floor(_Tp __x) noexcept
466  { return std::__bit_floor(__x); }
467 
468  // _GLIBCXX_RESOLVE_LIB_DEFECTS
469  // 3656. Inconsistent bit operations returning a count
470  /// The smallest integer greater than the base-2 logarithm of `x`.
471  template<__unsigned_integer _Tp>
472  constexpr int
473  bit_width(_Tp __x) noexcept
474  { return std::__bit_width(__x); }
475 #endif // defined (__cpp_lib_int_pow2)
476 
477 #ifdef __cpp_lib_endian // C++ >= 20
478 
479  /// Byte order constants
480  /**
481  * The platform endianness can be checked by comparing `std::endian::native`
482  * to one of `std::endian::big` or `std::endian::little`.
483  *
484  * @since C++20
485  */
486  enum class endian
487  {
488  little = __ORDER_LITTLE_ENDIAN__,
489  big = __ORDER_BIG_ENDIAN__,
490  native = __BYTE_ORDER__
491  };
492 #endif // __cpp_lib_endian
493 
494  /// @}
495 
496 _GLIBCXX_END_NAMESPACE_VERSION
497 } // namespace std
498 
499 #endif // C++14
500 #endif // _GLIBCXX_BIT