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#ifdef _GLIBCXX_SYSHDR
38#pragma GCC system_header
39#endif
40
41#define __glibcxx_want_span
42#include <bits/version.h>
43
44#ifdef __cpp_lib_span // C++ >= 20 && concepts
45#include <array>
46#include <cstddef>
47#include <bits/stl_iterator.h>
48#include <bits/ranges_base.h>
49namespace std _GLIBCXX_VISIBILITY(default)
50{
51_GLIBCXX_BEGIN_NAMESPACE_VERSION
52
53 inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
54
55 template<typename _Type, size_t _Extent>
56 class span;
57
58 namespace __detail
59 {
60 template<typename _Tp>
61 inline constexpr bool __is_span = false;
62
63 template<typename _Tp, size_t _Num>
64 inline constexpr bool __is_span<span<_Tp, _Num>> = true;
65
66 template<typename _Tp>
67 inline constexpr bool __is_std_array = false;
68
69 template<typename _Tp, size_t _Num>
70 inline constexpr bool __is_std_array<std::array<_Tp, _Num>> = true;
71
72 template<size_t _Extent>
73 class __extent_storage
74 {
75 public:
76 constexpr
77 __extent_storage(size_t) noexcept
78 { }
79
80 static constexpr size_t
81 _M_extent() noexcept
82 { return _Extent; }
83 };
84
85 template<>
86 class __extent_storage<dynamic_extent>
87 {
88 public:
89 constexpr
90 __extent_storage(size_t __extent) noexcept
91 : _M_extent_value(__extent)
92 { }
93
94 constexpr size_t
95 _M_extent() const noexcept
96 { return this->_M_extent_value; }
97
98 private:
99 size_t _M_extent_value;
100 };
101 } // namespace __detail
102
103 template<typename _Type, size_t _Extent = dynamic_extent>
104 class span
105 {
106 template<size_t _Offset, size_t _Count>
107 static constexpr size_t
108 _S_subspan_extent()
109 {
110 if constexpr (_Count != dynamic_extent)
111 return _Count;
112 else if constexpr (extent != dynamic_extent)
113 return _Extent - _Offset;
114 else
115 return dynamic_extent;
116 }
117
118 // _GLIBCXX_RESOLVE_LIB_DEFECTS
119 // 3255. span's array constructor is too strict
120 template<typename _Tp, size_t _ArrayExtent>
121 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
122 using __is_compatible_array = __is_array_convertible<_Type, _Tp>;
123
124 template<typename _Ref>
125 using __is_compatible_ref
126 = __is_array_convertible<_Type, remove_reference_t<_Ref>>;
127
128 // Nested type so that _Type is not an associated class of iterator.
129 struct __iter_tag;
130
131 public:
132 // member types
133 using element_type = _Type;
134 using value_type = remove_cv_t<_Type>;
135 using size_type = size_t;
136 using difference_type = ptrdiff_t;
137 using pointer = _Type*;
138 using const_pointer = const _Type*;
139 using reference = element_type&;
140 using const_reference = const element_type&;
141 using iterator = __gnu_cxx::__normal_iterator<pointer, __iter_tag>;
142 using reverse_iterator = std::reverse_iterator<iterator>;
143#if __cplusplus > 202002L
144 using const_iterator = std::const_iterator<iterator>;
145 using const_reverse_iterator = std::const_iterator<reverse_iterator>;
146#endif
147
148 // member constants
149 static constexpr size_t extent = _Extent;
150
151 // constructors, copy and assignment
152
153 constexpr
154 span() noexcept
155 requires (_Extent == dynamic_extent || _Extent == 0)
156 : _M_ptr(nullptr), _M_extent(0)
157 { }
158
159 template<contiguous_iterator _It>
160 requires __is_compatible_ref<iter_reference_t<_It>>::value
161 constexpr explicit(extent != dynamic_extent)
162 span(_It __first, size_type __count)
163 noexcept
164 : _M_ptr(std::to_address(__first)), _M_extent(__count)
165 {
166 if constexpr (_Extent != dynamic_extent)
167 {
168 __glibcxx_assert(__count == _Extent);
169 }
170 __glibcxx_requires_valid_range(__first, __first + __count);
171 }
172
173 template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
174 requires __is_compatible_ref<iter_reference_t<_It>>::value
175 && (!is_convertible_v<_End, size_type>)
176 constexpr explicit(extent != dynamic_extent)
177 span(_It __first, _End __last)
178 noexcept(noexcept(__last - __first))
179 : _M_ptr(std::to_address(__first)),
180 _M_extent(static_cast<size_type>(__last - __first))
181 {
182 if constexpr (_Extent != dynamic_extent)
183 {
184 __glibcxx_assert((__last - __first) == _Extent);
185 }
186 __glibcxx_requires_valid_range(__first, __last);
187 }
188
189 template<size_t _ArrayExtent>
190 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
191 constexpr
192 span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
193 : _M_ptr(__arr), _M_extent(_ArrayExtent)
194 { }
195
196 template<typename _Tp, size_t _ArrayExtent>
197 requires __is_compatible_array<_Tp, _ArrayExtent>::value
198 constexpr
199 span(array<_Tp, _ArrayExtent>& __arr) noexcept
200 : _M_ptr(__arr.data()), _M_extent(_ArrayExtent)
201 { }
202
203 template<typename _Tp, size_t _ArrayExtent>
204 requires __is_compatible_array<const _Tp, _ArrayExtent>::value
205 constexpr
206 span(const array<_Tp, _ArrayExtent>& __arr) noexcept
207 : _M_ptr(__arr.data()), _M_extent(_ArrayExtent)
208 { }
209
210 template<typename _Range>
211 requires (!__detail::__is_span<remove_cvref_t<_Range>>)
212 && (!__detail::__is_std_array<remove_cvref_t<_Range>>)
213 && (!is_array_v<remove_cvref_t<_Range>>)
214 && ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
215 && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
216 && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
217 constexpr explicit(extent != dynamic_extent)
218 span(_Range&& __range)
219 noexcept(noexcept(ranges::data(__range))
220 && noexcept(ranges::size(__range)))
221 : _M_ptr(ranges::data(__range)), _M_extent(ranges::size(__range))
222 {
223 if constexpr (extent != dynamic_extent)
224 {
225 __glibcxx_assert(ranges::size(__range) == extent);
226 }
227 }
228
229 constexpr
230 span(const span&) noexcept = default;
231
232 template<typename _OType, size_t _OExtent>
233 requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
234 || _Extent == _OExtent)
235 && (__is_array_convertible<_Type, _OType>::value)
236 constexpr
237 explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
238 span(const span<_OType, _OExtent>& __s) noexcept
239 : _M_ptr(__s.data()), _M_extent(__s.size())
240 {
241 if constexpr (extent != dynamic_extent)
242 {
243 __glibcxx_assert(__s.size() == extent);
244 }
245 }
246
247 ~span() noexcept = default;
248
249 constexpr span&
250 operator=(const span&) noexcept = default;
251
252 // observers
253
254 [[nodiscard]]
255 constexpr size_type
256 size() const noexcept
257 { return this->_M_extent._M_extent(); }
258
259 [[nodiscard]]
260 constexpr size_type
261 size_bytes() const noexcept
262 { return this->_M_extent._M_extent() * sizeof(element_type); }
263
264 [[nodiscard]]
265 constexpr bool
266 empty() const noexcept
267 { return size() == 0; }
268
269 // element access
270
271 [[nodiscard]]
272 constexpr reference
273 front() const noexcept
274 {
275 __glibcxx_assert(!empty());
276 return *this->_M_ptr;
277 }
278
279 [[nodiscard]]
280 constexpr reference
281 back() const noexcept
282 {
283 __glibcxx_assert(!empty());
284 return *(this->_M_ptr + (size() - 1));
285 }
286
287 [[nodiscard]]
288 constexpr reference
289 operator[](size_type __idx) const noexcept
290 {
291 __glibcxx_assert(__idx < size());
292 return *(this->_M_ptr + __idx);
293 }
294
295#if __cpp_lib_span >= 202311L // >= C++26
296 [[nodiscard]]
297 constexpr reference
298 at(size_type __idx) const
299 {
300 if (__idx >= size())
301 __throw_out_of_range_fmt(__N("span::at(%zu) out-of-range for span "
302 "of size %zu"), __idx, this->size());
303 return *(this->_M_ptr + __idx);
304 }
305#endif
306
307 [[nodiscard]]
308 constexpr pointer
309 data() const noexcept
310 { return this->_M_ptr; }
311
312 // iterator support
313
314 [[nodiscard]]
315 constexpr iterator
316 begin() const noexcept
317 { return iterator(this->_M_ptr); }
318
319 [[nodiscard]]
320 constexpr iterator
321 end() const noexcept
322 { return iterator(this->_M_ptr + this->size()); }
323
324 [[nodiscard]]
325 constexpr reverse_iterator
326 rbegin() const noexcept
327 { return reverse_iterator(this->end()); }
328
329 [[nodiscard]]
330 constexpr reverse_iterator
331 rend() const noexcept
332 { return reverse_iterator(this->begin()); }
333
334#if __cplusplus > 202002L
335 [[nodiscard]]
336 constexpr const_iterator
337 cbegin() const noexcept
338 { return begin(); }
339
340 [[nodiscard]]
341 constexpr const_iterator
342 cend() const noexcept
343 { return end(); }
344
345 [[nodiscard]]
346 constexpr const_reverse_iterator
347 crbegin() const noexcept
348 { return rbegin(); }
349
350 [[nodiscard]]
351 constexpr const_reverse_iterator
352 crend() const noexcept
353 { return rend(); }
354#endif
355
356 // subviews
357
358 template<size_t _Count>
359 [[nodiscard]]
360 constexpr span<element_type, _Count>
361 first() const noexcept
362 {
363 if constexpr (_Extent == dynamic_extent)
364 __glibcxx_assert(_Count <= size());
365 else
366 static_assert(_Count <= extent);
367 using _Sp = span<element_type, _Count>;
368 return _Sp{ this->data(), _Count };
369 }
370
371 [[nodiscard]]
372 constexpr span<element_type, dynamic_extent>
373 first(size_type __count) const noexcept
374 {
375 __glibcxx_assert(__count <= size());
376 return { this->data(), __count };
377 }
378
379 template<size_t _Count>
380 [[nodiscard]]
381 constexpr span<element_type, _Count>
382 last() const noexcept
383 {
384 if constexpr (_Extent == dynamic_extent)
385 __glibcxx_assert(_Count <= size());
386 else
387 static_assert(_Count <= extent);
388 using _Sp = span<element_type, _Count>;
389 return _Sp{ this->data() + (this->size() - _Count), _Count };
390 }
391
392 [[nodiscard]]
393 constexpr span<element_type, dynamic_extent>
394 last(size_type __count) const noexcept
395 {
396 __glibcxx_assert(__count <= size());
397 return { this->data() + (this->size() - __count), __count };
398 }
399
400 template<size_t _Offset, size_t _Count = dynamic_extent>
401 [[nodiscard]]
402 constexpr auto
403 subspan() const noexcept
404 -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
405 {
406 if constexpr (_Extent == dynamic_extent)
407 {
408 __glibcxx_assert(_Offset <= size());
409 }
410 else
411 static_assert(_Offset <= extent);
412
413 using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
414
415 if constexpr (_Count == dynamic_extent)
416 return _Sp{ this->data() + _Offset, this->size() - _Offset };
417 else
418 {
419 if constexpr (_Extent == dynamic_extent)
420 {
421 __glibcxx_assert(_Count <= size());
422 __glibcxx_assert(_Count <= (size() - _Offset));
423 }
424 else
425 {
426 static_assert(_Count <= extent);
427 static_assert(_Count <= (extent - _Offset));
428 }
429 return _Sp{ this->data() + _Offset, _Count };
430 }
431 }
432
433 [[nodiscard]]
434 constexpr span<element_type, dynamic_extent>
435 subspan(size_type __offset, size_type __count = dynamic_extent) const
436 noexcept
437 {
438 __glibcxx_assert(__offset <= size());
439 if (__count == dynamic_extent)
440 __count = this->size() - __offset;
441 else
442 {
443 __glibcxx_assert(__count <= size());
444 __glibcxx_assert(__offset + __count <= size());
445 }
446 return {this->data() + __offset, __count};
447 }
448
449 private:
450 pointer _M_ptr;
451 [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
452 };
453
454 // deduction guides
455
456 template<typename _Type, size_t _ArrayExtent>
457 span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
458
459 template<typename _Type, size_t _ArrayExtent>
460 span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
461
462 template<typename _Type, size_t _ArrayExtent>
463 span(const array<_Type, _ArrayExtent>&)
464 -> span<const _Type, _ArrayExtent>;
465
466 template<contiguous_iterator _Iter, typename _End>
467 span(_Iter, _End)
468 -> span<remove_reference_t<iter_reference_t<_Iter>>>;
469
470 template<ranges::contiguous_range _Range>
471 span(_Range &&)
472 -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
473
474 template<typename _Type, size_t _Extent>
475 [[nodiscard]]
476 inline
477 span<const byte, _Extent == dynamic_extent
478 ? dynamic_extent : _Extent * sizeof(_Type)>
479 as_bytes(span<_Type, _Extent> __sp) noexcept
480 {
481 auto data = reinterpret_cast<const byte*>(__sp.data());
482 auto size = __sp.size_bytes();
483 constexpr auto extent = _Extent == dynamic_extent
484 ? dynamic_extent : _Extent * sizeof(_Type);
485 return span<const byte, extent>{data, size};
486 }
487
488 template<typename _Type, size_t _Extent>
489 requires (!is_const_v<_Type>)
490 inline
491 span<byte, _Extent == dynamic_extent
492 ? dynamic_extent : _Extent * sizeof(_Type)>
493 as_writable_bytes [[nodiscard]] (span<_Type, _Extent> __sp) noexcept
494 {
495 auto data = reinterpret_cast<byte*>(__sp.data());
496 auto size = __sp.size_bytes();
497 constexpr auto extent = _Extent == dynamic_extent
498 ? dynamic_extent : _Extent * sizeof(_Type);
499 return span<byte, extent>{data, size};
500 }
501
502 namespace ranges
503 {
504 // Opt-in to borrowed_range concept
505 template<typename _ElementType, size_t _Extent>
506 inline constexpr bool
507 enable_borrowed_range<span<_ElementType, _Extent>> = true;
508
509 // Opt-in to view concept
510 template<typename _ElementType, size_t _Extent>
511 inline constexpr bool
512 enable_view<span<_ElementType, _Extent>> = true;
513 }
514_GLIBCXX_END_NAMESPACE_VERSION
515} // namespace std
516#endif // __cpp_lib_span
517#endif // _GLIBCXX_SPAN
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition ptr_traits.h:232
_Tp * end(valarray< _Tp > &__va) noexcept
Return an iterator pointing to one past the last element of the valarray.
Definition valarray:1251
_Tp * begin(valarray< _Tp > &__va) noexcept
Return an iterator pointing to the first element of the valarray.
Definition valarray:1229
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.