libstdc++
bit
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1// <bit> -*- C++ -*-
2
3// Copyright (C) 2018-2020 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#include <bits/int_limits.h>
38
39namespace std _GLIBCXX_VISIBILITY(default)
40{
41_GLIBCXX_BEGIN_NAMESPACE_VERSION
42
43 /**
44 * @defgroup bit_manip Bit manipulation
45 * @ingroup numerics
46 *
47 * Utilities for examining and manipulating individual bits.
48 *
49 * @{
50 */
51
52 /// @cond undoc
53
54 template<typename _Tp>
55 constexpr _Tp
56 __rotl(_Tp __x, int __s) noexcept
57 {
58 constexpr auto _Nd = __detail::__int_limits<_Tp>::digits;
59 const int __r = __s % _Nd;
60 if (__r == 0)
61 return __x;
62 else if (__r > 0)
63 return (__x << __r) | (__x >> ((_Nd - __r) % _Nd));
64 else
65 return (__x >> -__r) | (__x << ((_Nd + __r) % _Nd)); // rotr(x, -r)
66 }
67
68 template<typename _Tp>
69 constexpr _Tp
70 __rotr(_Tp __x, int __s) noexcept
71 {
72 constexpr auto _Nd = __detail::__int_limits<_Tp>::digits;
73 const int __r = __s % _Nd;
74 if (__r == 0)
75 return __x;
76 else if (__r > 0)
77 return (__x >> __r) | (__x << ((_Nd - __r) % _Nd));
78 else
79 return (__x << -__r) | (__x >> ((_Nd + __r) % _Nd)); // rotl(x, -r)
80 }
81
82 template<typename _Tp>
83 constexpr int
84 __countl_zero(_Tp __x) noexcept
85 {
86 using std::__detail::__int_limits;
87 constexpr auto _Nd = __int_limits<_Tp>::digits;
88
89 if (__x == 0)
90 return _Nd;
91
92 constexpr auto _Nd_ull = __int_limits<unsigned long long>::digits;
93 constexpr auto _Nd_ul = __int_limits<unsigned long>::digits;
94 constexpr auto _Nd_u = __int_limits<unsigned>::digits;
95
96 if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
97 {
98 constexpr int __diff = _Nd_u - _Nd;
99 return __builtin_clz(__x) - __diff;
100 }
101 else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
102 {
103 constexpr int __diff = _Nd_ul - _Nd;
104 return __builtin_clzl(__x) - __diff;
105 }
106 else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
107 {
108 constexpr int __diff = _Nd_ull - _Nd;
109 return __builtin_clzll(__x) - __diff;
110 }
111 else // (_Nd > _Nd_ull)
112 {
113 static_assert(_Nd <= (2 * _Nd_ull),
114 "Maximum supported integer size is 128-bit");
115
116 unsigned long long __high = __x >> _Nd_ull;
117 if (__high != 0)
118 {
119 constexpr int __diff = (2 * _Nd_ull) - _Nd;
120 return __builtin_clzll(__high) - __diff;
121 }
122 constexpr auto __max_ull = __int_limits<unsigned long long>::max();
123 unsigned long long __low = __x & __max_ull;
124 return (_Nd - _Nd_ull) + __builtin_clzll(__low);
125 }
126 }
127
128 template<typename _Tp>
129 constexpr int
130 __countl_one(_Tp __x) noexcept
131 {
133 return __detail::__int_limits<_Tp>::digits;
134 return std::__countl_zero<_Tp>((_Tp)~__x);
135 }
136
137 template<typename _Tp>
138 constexpr int
139 __countr_zero(_Tp __x) noexcept
140 {
141 using std::__detail::__int_limits;
142 constexpr auto _Nd = __int_limits<_Tp>::digits;
143
144 if (__x == 0)
145 return _Nd;
146
147 constexpr auto _Nd_ull = __int_limits<unsigned long long>::digits;
148 constexpr auto _Nd_ul = __int_limits<unsigned long>::digits;
149 constexpr auto _Nd_u = __int_limits<unsigned>::digits;
150
151 if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
152 return __builtin_ctz(__x);
153 else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
154 return __builtin_ctzl(__x);
155 else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
156 return __builtin_ctzll(__x);
157 else // (_Nd > _Nd_ull)
158 {
159 static_assert(_Nd <= (2 * _Nd_ull),
160 "Maximum supported integer size is 128-bit");
161
162 constexpr auto __max_ull = __int_limits<unsigned long long>::max();
163 unsigned long long __low = __x & __max_ull;
164 if (__low != 0)
165 return __builtin_ctzll(__low);
166 unsigned long long __high = __x >> _Nd_ull;
167 return __builtin_ctzll(__high) + _Nd_ull;
168 }
169 }
170
171 template<typename _Tp>
172 constexpr int
173 __countr_one(_Tp __x) noexcept
174 {
176 return __detail::__int_limits<_Tp>::digits;
177 return std::__countr_zero((_Tp)~__x);
178 }
179
180 template<typename _Tp>
181 constexpr int
182 __popcount(_Tp __x) noexcept
183 {
184 using std::__detail::__int_limits;
185 constexpr auto _Nd = __int_limits<_Tp>::digits;
186
187 if (__x == 0)
188 return 0;
189
190 constexpr auto _Nd_ull = __int_limits<unsigned long long>::digits;
191 constexpr auto _Nd_ul = __int_limits<unsigned long>::digits;
192 constexpr auto _Nd_u = __int_limits<unsigned>::digits;
193
194 if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_u)
195 return __builtin_popcount(__x);
196 else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ul)
197 return __builtin_popcountl(__x);
198 else if _GLIBCXX17_CONSTEXPR (_Nd <= _Nd_ull)
199 return __builtin_popcountll(__x);
200 else // (_Nd > _Nd_ull)
201 {
202 static_assert(_Nd <= (2 * _Nd_ull),
203 "Maximum supported integer size is 128-bit");
204
205 constexpr auto __max_ull = __int_limits<unsigned long long>::max();
206 unsigned long long __low = __x & __max_ull;
207 unsigned long long __high = __x >> _Nd_ull;
208 return __builtin_popcountll(__low) + __builtin_popcountll(__high);
209 }
210 }
211
212 template<typename _Tp>
213 constexpr bool
214 __has_single_bit(_Tp __x) noexcept
215 { return std::__popcount(__x) == 1; }
216
217 template<typename _Tp>
218 constexpr _Tp
219 __bit_ceil(_Tp __x) noexcept
220 {
221 using std::__detail::__int_limits;
222 constexpr auto _Nd = __int_limits<_Tp>::digits;
223 if (__x == 0 || __x == 1)
224 return 1;
225 auto __shift_exponent = _Nd - std::__countl_zero((_Tp)(__x - 1u));
226 // If the shift exponent equals _Nd then the correct result is not
227 // representable as a value of _Tp, and so the result is undefined.
228 // Want that undefined behaviour to be detected in constant expressions,
229 // by UBSan, and by debug assertions.
230#ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
231 if (!__builtin_is_constant_evaluated())
232 {
233 __glibcxx_assert( __shift_exponent != __int_limits<_Tp>::digits );
234 }
235#endif
236 using __promoted_type = decltype(__x << 1);
237 if _GLIBCXX17_CONSTEXPR (!is_same<__promoted_type, _Tp>::value)
238 {
239 // If __x undergoes integral promotion then shifting by _Nd is
240 // not undefined. In order to make the shift undefined, so that
241 // it is diagnosed in constant expressions and by UBsan, we also
242 // need to "promote" the shift exponent to be too large for the
243 // promoted type.
244 const int __extra_exp = sizeof(__promoted_type) / sizeof(_Tp) / 2;
245 __shift_exponent |= (__shift_exponent & _Nd) << __extra_exp;
246 }
247 return (_Tp)1u << __shift_exponent;
248 }
249
250 template<typename _Tp>
251 constexpr _Tp
252 __bit_floor(_Tp __x) noexcept
253 {
254 constexpr auto _Nd = __detail::__int_limits<_Tp>::digits;
255 if (__x == 0)
256 return 0;
257 return (_Tp)1u << (_Nd - std::__countl_zero((_Tp)(__x >> 1)));
258 }
259
260 template<typename _Tp>
261 constexpr _Tp
262 __bit_width(_Tp __x) noexcept
263 {
264 constexpr auto _Nd = __detail::__int_limits<_Tp>::digits;
265 return _Nd - std::__countl_zero(__x);
266 }
267
268 /// @endcond
269
270#if __cplusplus > 201703L
271
272#define __cpp_lib_bitops 201907L
273
274 /// @cond undoc
275 template<typename _Tp, typename _Up = _Tp>
276 using _If_is_unsigned_integer
277 = enable_if_t<__is_unsigned_integer<_Tp>::value, _Up>;
278 /// @endcond
279
280 // [bit.rot], rotating
281
282 /// Rotate `x` to the left by `s` bits.
283 template<typename _Tp>
284 [[nodiscard]] constexpr _If_is_unsigned_integer<_Tp>
285 rotl(_Tp __x, int __s) noexcept
286 { return std::__rotl(__x, __s); }
287
288 /// Rotate `x` to the right by `s` bits.
289 template<typename _Tp>
290 [[nodiscard]] constexpr _If_is_unsigned_integer<_Tp>
291 rotr(_Tp __x, int __s) noexcept
292 { return std::__rotr(__x, __s); }
293
294 // [bit.count], counting
295
296 /// The number of contiguous zero bits, starting from the highest bit.
297 template<typename _Tp>
298 constexpr _If_is_unsigned_integer<_Tp, int>
299 countl_zero(_Tp __x) noexcept
300 { return std::__countl_zero(__x); }
301
302 /// The number of contiguous one bits, starting from the highest bit.
303 template<typename _Tp>
304 constexpr _If_is_unsigned_integer<_Tp, int>
305 countl_one(_Tp __x) noexcept
306 { return std::__countl_one(__x); }
307
308 /// The number of contiguous zero bits, starting from the lowest bit.
309 template<typename _Tp>
310 constexpr _If_is_unsigned_integer<_Tp, int>
311 countr_zero(_Tp __x) noexcept
312 { return std::__countr_zero(__x); }
313
314 /// The number of contiguous one bits, starting from the lowest bit.
315 template<typename _Tp>
316 constexpr _If_is_unsigned_integer<_Tp, int>
317 countr_one(_Tp __x) noexcept
318 { return std::__countr_one(__x); }
319
320 /// The number of bits set in `x`.
321 template<typename _Tp>
322 constexpr _If_is_unsigned_integer<_Tp, int>
323 popcount(_Tp __x) noexcept
324 { return std::__popcount(__x); }
325
326 // [bit.pow.two], integral powers of 2
327
328#define __cpp_lib_int_pow2 202002L
329
330 /// True if `x` is a power of two, false otherwise.
331 template<typename _Tp>
332 constexpr _If_is_unsigned_integer<_Tp, bool>
333 has_single_bit(_Tp __x) noexcept
334 { return std::__has_single_bit(__x); }
335
336 /// The smallest power-of-two not less than `x`.
337 template<typename _Tp>
338 constexpr _If_is_unsigned_integer<_Tp>
339 bit_ceil(_Tp __x) noexcept
340 { return std::__bit_ceil(__x); }
341
342 /// The largest power-of-two not greater than `x`.
343 template<typename _Tp>
344 constexpr _If_is_unsigned_integer<_Tp>
345 bit_floor(_Tp __x) noexcept
346 { return std::__bit_floor(__x); }
347
348 /// The smallest integer greater than the base-2 logarithm of `x`.
349 template<typename _Tp>
350 constexpr _If_is_unsigned_integer<_Tp>
351 bit_width(_Tp __x) noexcept
352 { return std::__bit_width(__x); }
353
354#define __cpp_lib_endian 201907L
355
356 /// Byte order
357 enum class endian
358 {
359 little = __ORDER_LITTLE_ENDIAN__,
360 big = __ORDER_BIG_ENDIAN__,
361 native = __BYTE_ORDER__
362 };
363#endif // C++2a
364
365 /// @}
366
367_GLIBCXX_END_NAMESPACE_VERSION
368} // namespace std
369
370#endif // C++14
371#endif // _GLIBCXX_BIT
constexpr const _Tp & max(const _Tp &, const _Tp &)
This does what you think it does.
Definition: stl_algobase.h:254
ISO C++ entities toplevel namespace is std.