libstdc++
span
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1// Components for manipulating non-owning sequences of objects -*- C++ -*-
2
3// Copyright (C) 2019-2024 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 span
26 * This is a Standard C++ Library header.
27 */
28
29//
30// P0122 span library
31// Contributed by ThePhD
32//
33
34#ifndef _GLIBCXX_SPAN
35#define _GLIBCXX_SPAN 1
36
37#pragma GCC system_header
38
39#define __glibcxx_want_span
40#include <bits/version.h>
41
42#ifdef __cpp_lib_span // C++ >= 20 && concepts
43#include <array>
44#include <cstddef>
45#include <bits/stl_iterator.h>
46#include <bits/ranges_base.h>
47namespace std _GLIBCXX_VISIBILITY(default)
48{
49_GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51 inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
52
53 template<typename _Type, size_t _Extent>
54 class span;
55
56 namespace __detail
57 {
58 template<typename _Tp>
59 inline constexpr bool __is_span = false;
60
61 template<typename _Tp, size_t _Num>
62 inline constexpr bool __is_span<span<_Tp, _Num>> = true;
63
64 template<typename _Tp>
65 inline constexpr bool __is_std_array = false;
66
67 template<typename _Tp, size_t _Num>
68 inline constexpr bool __is_std_array<std::array<_Tp, _Num>> = true;
69
70 template<size_t _Extent>
71 class __extent_storage
72 {
73 public:
74 constexpr
75 __extent_storage(size_t) noexcept
76 { }
77
78 static constexpr size_t
79 _M_extent() noexcept
80 { return _Extent; }
81 };
82
83 template<>
84 class __extent_storage<dynamic_extent>
85 {
86 public:
87 constexpr
88 __extent_storage(size_t __extent) noexcept
89 : _M_extent_value(__extent)
90 { }
91
92 constexpr size_t
93 _M_extent() const noexcept
94 { return this->_M_extent_value; }
95
96 private:
97 size_t _M_extent_value;
98 };
99 } // namespace __detail
100
101 template<typename _Type, size_t _Extent = dynamic_extent>
102 class span
103 {
104 template<size_t _Offset, size_t _Count>
105 static constexpr size_t
106 _S_subspan_extent()
107 {
108 if constexpr (_Count != dynamic_extent)
109 return _Count;
110 else if constexpr (extent != dynamic_extent)
111 return _Extent - _Offset;
112 else
113 return dynamic_extent;
114 }
115
116 // _GLIBCXX_RESOLVE_LIB_DEFECTS
117 // 3255. span's array constructor is too strict
118 template<typename _Tp, size_t _ArrayExtent>
119 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
120 using __is_compatible_array = __is_array_convertible<_Type, _Tp>;
121
122 template<typename _Ref>
123 using __is_compatible_ref
124 = __is_array_convertible<_Type, remove_reference_t<_Ref>>;
125
126 public:
127 // member types
128 using element_type = _Type;
129 using value_type = remove_cv_t<_Type>;
130 using size_type = size_t;
131 using difference_type = ptrdiff_t;
132 using pointer = _Type*;
133 using const_pointer = const _Type*;
134 using reference = element_type&;
135 using const_reference = const element_type&;
136 using iterator = __gnu_cxx::__normal_iterator<pointer, span>;
137 using reverse_iterator = std::reverse_iterator<iterator>;
138#if __cplusplus > 202002L
139 using const_iterator = std::const_iterator<iterator>;
140 using const_reverse_iterator = std::const_iterator<reverse_iterator>;
141#endif
142
143 // member constants
144 static constexpr size_t extent = _Extent;
145
146 // constructors, copy and assignment
147
148 constexpr
149 span() noexcept
150 requires (_Extent == dynamic_extent || _Extent == 0)
151 : _M_ptr(nullptr), _M_extent(0)
152 { }
153
154 template<contiguous_iterator _It>
155 requires __is_compatible_ref<iter_reference_t<_It>>::value
156 constexpr explicit(extent != dynamic_extent)
157 span(_It __first, size_type __count)
158 noexcept
159 : _M_ptr(std::to_address(__first)), _M_extent(__count)
160 {
161 if constexpr (_Extent != dynamic_extent)
162 {
163 __glibcxx_assert(__count == _Extent);
164 }
165 __glibcxx_requires_valid_range(__first, __first + __count);
166 }
167
168 template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
169 requires __is_compatible_ref<iter_reference_t<_It>>::value
170 && (!is_convertible_v<_End, size_type>)
171 constexpr explicit(extent != dynamic_extent)
172 span(_It __first, _End __last)
173 noexcept(noexcept(__last - __first))
174 : _M_ptr(std::to_address(__first)),
175 _M_extent(static_cast<size_type>(__last - __first))
176 {
177 if constexpr (_Extent != dynamic_extent)
178 {
179 __glibcxx_assert((__last - __first) == _Extent);
180 }
181 __glibcxx_requires_valid_range(__first, __last);
182 }
183
184 template<size_t _ArrayExtent>
185 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
186 constexpr
187 span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
188 : span(static_cast<pointer>(__arr), _ArrayExtent)
189 { }
190
191 template<typename _Tp, size_t _ArrayExtent>
192 requires __is_compatible_array<_Tp, _ArrayExtent>::value
193 constexpr
194 span(array<_Tp, _ArrayExtent>& __arr) noexcept
195 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
196 { }
197
198 template<typename _Tp, size_t _ArrayExtent>
199 requires __is_compatible_array<const _Tp, _ArrayExtent>::value
200 constexpr
201 span(const array<_Tp, _ArrayExtent>& __arr) noexcept
202 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
203 { }
204
205 template<typename _Range>
206 requires (!__detail::__is_span<remove_cvref_t<_Range>>)
207 && (!__detail::__is_std_array<remove_cvref_t<_Range>>)
208 && (!is_array_v<remove_cvref_t<_Range>>)
209 && ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
210 && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
211 && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
212 constexpr explicit(extent != dynamic_extent)
213 span(_Range&& __range)
214 noexcept(noexcept(ranges::data(__range))
215 && noexcept(ranges::size(__range)))
216 : span(ranges::data(__range), ranges::size(__range))
217 {
218 if constexpr (extent != dynamic_extent)
219 {
220 __glibcxx_assert(ranges::size(__range) == extent);
221 }
222 }
223
224 constexpr
225 span(const span&) noexcept = default;
226
227 template<typename _OType, size_t _OExtent>
228 requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
229 || _Extent == _OExtent)
230 && (__is_array_convertible<_Type, _OType>::value)
231 constexpr
232 explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
233 span(const span<_OType, _OExtent>& __s) noexcept
234 : _M_extent(__s.size()), _M_ptr(__s.data())
235 {
236 if constexpr (extent != dynamic_extent)
237 {
238 __glibcxx_assert(__s.size() == extent);
239 }
240 }
241
242 ~span() noexcept = default;
243
244 constexpr span&
245 operator=(const span&) noexcept = default;
246
247 // observers
248
249 [[nodiscard]]
250 constexpr size_type
251 size() const noexcept
252 { return this->_M_extent._M_extent(); }
253
254 [[nodiscard]]
255 constexpr size_type
256 size_bytes() const noexcept
257 { return this->_M_extent._M_extent() * sizeof(element_type); }
258
259 [[nodiscard]]
260 constexpr bool
261 empty() const noexcept
262 { return size() == 0; }
263
264 // element access
265
266 [[nodiscard]]
267 constexpr reference
268 front() const noexcept
269 {
270 __glibcxx_assert(!empty());
271 return *this->_M_ptr;
272 }
273
274 [[nodiscard]]
275 constexpr reference
276 back() const noexcept
277 {
278 __glibcxx_assert(!empty());
279 return *(this->_M_ptr + (size() - 1));
280 }
281
282 [[nodiscard]]
283 constexpr reference
284 operator[](size_type __idx) const noexcept
285 {
286 __glibcxx_assert(__idx < size());
287 return *(this->_M_ptr + __idx);
288 }
289
290 [[nodiscard]]
291 constexpr reference
292 at(size_type __idx) const
293 {
294 if (__idx >= size())
295 __throw_out_of_range_fmt(__N("span::at(%zu) out-of-range for span "
296 "of size %zu"), __idx, this->size());
297 return *(this->_M_ptr + __idx);
298 }
299
300 [[nodiscard]]
301 constexpr pointer
302 data() const noexcept
303 { return this->_M_ptr; }
304
305 // iterator support
306
307 [[nodiscard]]
308 constexpr iterator
309 begin() const noexcept
310 { return iterator(this->_M_ptr); }
311
312 [[nodiscard]]
313 constexpr iterator
314 end() const noexcept
315 { return iterator(this->_M_ptr + this->size()); }
316
317 [[nodiscard]]
318 constexpr reverse_iterator
319 rbegin() const noexcept
320 { return reverse_iterator(this->end()); }
321
322 [[nodiscard]]
323 constexpr reverse_iterator
324 rend() const noexcept
325 { return reverse_iterator(this->begin()); }
326
327#if __cplusplus > 202002L
328 [[nodiscard]]
329 constexpr const_iterator
330 cbegin() const noexcept
331 { return begin(); }
332
333 [[nodiscard]]
334 constexpr const_iterator
335 cend() const noexcept
336 { return end(); }
337
338 [[nodiscard]]
339 constexpr const_reverse_iterator
340 crbegin() const noexcept
341 { return rbegin(); }
342
343 [[nodiscard]]
344 constexpr const_reverse_iterator
345 crend() const noexcept
346 { return rend(); }
347#endif
348
349 // subviews
350
351 template<size_t _Count>
352 [[nodiscard]]
353 constexpr span<element_type, _Count>
354 first() const noexcept
355 {
356 if constexpr (_Extent == dynamic_extent)
357 __glibcxx_assert(_Count <= size());
358 else
359 static_assert(_Count <= extent);
360 using _Sp = span<element_type, _Count>;
361 return _Sp{ this->data(), _Count };
362 }
363
364 [[nodiscard]]
365 constexpr span<element_type, dynamic_extent>
366 first(size_type __count) const noexcept
367 {
368 __glibcxx_assert(__count <= size());
369 return { this->data(), __count };
370 }
371
372 template<size_t _Count>
373 [[nodiscard]]
374 constexpr span<element_type, _Count>
375 last() const noexcept
376 {
377 if constexpr (_Extent == dynamic_extent)
378 __glibcxx_assert(_Count <= size());
379 else
380 static_assert(_Count <= extent);
381 using _Sp = span<element_type, _Count>;
382 return _Sp{ this->data() + (this->size() - _Count), _Count };
383 }
384
385 [[nodiscard]]
386 constexpr span<element_type, dynamic_extent>
387 last(size_type __count) const noexcept
388 {
389 __glibcxx_assert(__count <= size());
390 return { this->data() + (this->size() - __count), __count };
391 }
392
393 template<size_t _Offset, size_t _Count = dynamic_extent>
394 [[nodiscard]]
395 constexpr auto
396 subspan() const noexcept
397 -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
398 {
399 if constexpr (_Extent == dynamic_extent)
400 {
401 __glibcxx_assert(_Offset <= size());
402 }
403 else
404 static_assert(_Offset <= extent);
405
406 using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
407
408 if constexpr (_Count == dynamic_extent)
409 return _Sp{ this->data() + _Offset, this->size() - _Offset };
410 else
411 {
412 if constexpr (_Extent == dynamic_extent)
413 {
414 __glibcxx_assert(_Count <= size());
415 __glibcxx_assert(_Count <= (size() - _Offset));
416 }
417 else
418 {
419 static_assert(_Count <= extent);
420 static_assert(_Count <= (extent - _Offset));
421 }
422 return _Sp{ this->data() + _Offset, _Count };
423 }
424 }
425
426 [[nodiscard]]
427 constexpr span<element_type, dynamic_extent>
428 subspan(size_type __offset, size_type __count = dynamic_extent) const
429 noexcept
430 {
431 __glibcxx_assert(__offset <= size());
432 if (__count == dynamic_extent)
433 __count = this->size() - __offset;
434 else
435 {
436 __glibcxx_assert(__count <= size());
437 __glibcxx_assert(__offset + __count <= size());
438 }
439 return {this->data() + __offset, __count};
440 }
441
442 private:
443 pointer _M_ptr;
444 [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
445 };
446
447 // deduction guides
448
449 template<typename _Type, size_t _ArrayExtent>
450 span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
451
452 template<typename _Type, size_t _ArrayExtent>
453 span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
454
455 template<typename _Type, size_t _ArrayExtent>
456 span(const array<_Type, _ArrayExtent>&)
457 -> span<const _Type, _ArrayExtent>;
458
459 template<contiguous_iterator _Iter, typename _End>
460 span(_Iter, _End)
461 -> span<remove_reference_t<iter_reference_t<_Iter>>>;
462
463 template<ranges::contiguous_range _Range>
464 span(_Range &&)
465 -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
466
467 template<typename _Type, size_t _Extent>
468 [[nodiscard]]
469 inline
470 span<const byte, _Extent == dynamic_extent
471 ? dynamic_extent : _Extent * sizeof(_Type)>
472 as_bytes(span<_Type, _Extent> __sp) noexcept
473 {
474 auto data = reinterpret_cast<const byte*>(__sp.data());
475 auto size = __sp.size_bytes();
476 constexpr auto extent = _Extent == dynamic_extent
477 ? dynamic_extent : _Extent * sizeof(_Type);
478 return span<const byte, extent>{data, size};
479 }
480
481 template<typename _Type, size_t _Extent>
482 requires (!is_const_v<_Type>)
483 inline
484 span<byte, _Extent == dynamic_extent
485 ? dynamic_extent : _Extent * sizeof(_Type)>
486 as_writable_bytes [[nodiscard]] (span<_Type, _Extent> __sp) noexcept
487 {
488 auto data = reinterpret_cast<byte*>(__sp.data());
489 auto size = __sp.size_bytes();
490 constexpr auto extent = _Extent == dynamic_extent
491 ? dynamic_extent : _Extent * sizeof(_Type);
492 return span<byte, extent>{data, size};
493 }
494
495 namespace ranges
496 {
497 // Opt-in to borrowed_range concept
498 template<typename _ElementType, size_t _Extent>
499 inline constexpr bool
500 enable_borrowed_range<span<_ElementType, _Extent>> = true;
501
502 // Opt-in to view concept
503 template<typename _ElementType, size_t _Extent>
504 inline constexpr bool
505 enable_view<span<_ElementType, _Extent>> = true;
506 }
507_GLIBCXX_END_NAMESPACE_VERSION
508} // namespace std
509#endif // __cpp_lib_span
510#endif // _GLIBCXX_SPAN
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition ptr_traits.h:241
_Tp * end(valarray< _Tp > &__va) noexcept
Return an iterator pointing to one past the last element of the valarray.
Definition valarray:1243
_Tp * begin(valarray< _Tp > &__va) noexcept
Return an iterator pointing to the first element of the valarray.
Definition valarray:1221
ISO C++ entities toplevel namespace is std.
constexpr auto crend(const _Container &__cont) -> decltype(std::rend(__cont))
Return a reverse iterator pointing one past the first element of the const container.
constexpr auto rend(_Container &__cont) -> decltype(__cont.rend())
Return a reverse iterator pointing one past the first element of the container.
constexpr auto cend(const _Container &__cont) noexcept(noexcept(std::end(__cont))) -> decltype(std::end(__cont))
Return an iterator pointing to one past the last element of the const container.
constexpr auto empty(const _Container &__cont) noexcept(noexcept(__cont.empty())) -> decltype(__cont.empty())
Return whether a container is empty.
constexpr auto size(const _Container &__cont) noexcept(noexcept(__cont.size())) -> decltype(__cont.size())
Return the size of a container.
constexpr auto rbegin(_Container &__cont) -> decltype(__cont.rbegin())
Return a reverse iterator pointing to the last element of the container.
constexpr auto crbegin(const _Container &__cont) -> decltype(std::rbegin(__cont))
Return a reverse iterator pointing to the last element of the const container.
constexpr auto data(_Container &__cont) noexcept(noexcept(__cont.data())) -> decltype(__cont.data())
Return the data pointer of a container.
constexpr auto cbegin(const _Container &__cont) noexcept(noexcept(std::begin(__cont))) -> decltype(std::begin(__cont))
Return an iterator pointing to the first element of the const container.