libstdc++
span
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1// Components for manipulating non-owning sequences of objects -*- C++ -*-
2
3// Copyright (C) 2019-2020 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 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#if __cplusplus > 201703L
40
41#include <type_traits>
42#include <array>
43#include <bits/stl_iterator.h>
44#include <bits/range_access.h>
45
46#if __cpp_lib_concepts
47namespace std _GLIBCXX_VISIBILITY(default)
48{
49_GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51#define __cpp_lib_span 202002L
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 struct __is_std_span : false_type { };
62
63 template<typename _Tp, size_t _Num>
64 struct __is_std_span<span<_Tp, _Num>> : true_type { };
65
66 template<typename _Tp>
67 struct __is_std_array : false_type { };
68
69 template<typename _Tp, size_t _Num>
70 struct __is_std_array<_GLIBCXX_STD_C::array<_Tp, _Num>> : true_type { };
71
72#ifdef _GLIBCXX_DEBUG
73 template<typename _Tp, size_t _Num>
74 struct __is_std_array<__debug::array<_Tp, _Num>> : true_type { };
75#endif
76
77 template<size_t _Extent>
78 class __extent_storage
79 {
80 public:
81 constexpr
82 __extent_storage(size_t) noexcept
83 { }
84
85 static constexpr size_t
86 _M_extent() noexcept
87 { return _Extent; }
88 };
89
90 template<>
91 class __extent_storage<dynamic_extent>
92 {
93 public:
94 constexpr
95 __extent_storage(size_t __extent) noexcept
96 : _M_extent_value(__extent)
97 { }
98
99 constexpr size_t
100 _M_extent() const noexcept
101 { return this->_M_extent_value; }
102
103 private:
104 size_t _M_extent_value;
105 };
106 } // namespace __detail
107
108 template<typename _Type, size_t _Extent = dynamic_extent>
109 class span
110 {
111 template<size_t _Offset, size_t _Count>
112 static constexpr size_t
113 _S_subspan_extent()
114 {
115 if constexpr (_Count != dynamic_extent)
116 return _Count;
117 else if constexpr (extent != dynamic_extent)
118 return _Extent - _Offset;
119 else
120 return dynamic_extent;
121 }
122
123 // _GLIBCXX_RESOLVE_LIB_DEFECTS
124 // 3255. span's array constructor is too strict
125 template<typename _Tp, size_t _ArrayExtent>
126 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
127 using __is_compatible_array = __is_array_convertible<_Type, _Tp>;
128
129 template<typename _Ref>
130 using __is_compatible_ref
131 = __is_array_convertible<_Type, remove_reference_t<_Ref>>;
132
133 public:
134 // member types
135 using element_type = _Type;
136 using value_type = remove_cv_t<_Type>;
137 using size_type = size_t;
138 using difference_type = ptrdiff_t;
139 using pointer = _Type*;
140 using const_pointer = const _Type*;
141 using reference = element_type&;
142 using const_reference = const element_type&;
143 using iterator = __gnu_cxx::__normal_iterator<pointer, span>;
144 using reverse_iterator = std::reverse_iterator<iterator>;
145
146 // member constants
147 static constexpr size_t extent = _Extent;
148
149 // constructors, copy and assignment
150
151 constexpr
152 span() noexcept
153 requires ((_Extent + 1u) <= 1u)
154 : _M_extent(0), _M_ptr(nullptr)
155 { }
156
157 template<contiguous_iterator _It>
158 requires __is_compatible_ref<iter_reference_t<_It>>::value
159 constexpr explicit(extent != dynamic_extent)
160 span(_It __first, size_type __count)
161 noexcept
162 : _M_extent(__count), _M_ptr(std::to_address(__first))
163 {
164 if constexpr (_Extent != dynamic_extent)
165 {
166 __glibcxx_assert(__count == _Extent);
167 }
168 __glibcxx_requires_valid_range(__first, __first + __count);
169 }
170
171 template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
172 requires __is_compatible_ref<iter_reference_t<_It>>::value
173 && (!is_convertible_v<_End, size_type>)
174 constexpr explicit(extent != dynamic_extent)
175 span(_It __first, _End __last)
176 noexcept(noexcept(__last - __first))
177 : _M_extent(static_cast<size_type>(__last - __first)),
178 _M_ptr(std::to_address(__first))
179 {
180 if constexpr (_Extent != dynamic_extent)
181 {
182 __glibcxx_assert((__last - __first) == _Extent);
183 }
184 __glibcxx_requires_valid_range(__first, __last);
185 }
186
187 template<size_t _ArrayExtent>
188 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
189 constexpr
190 span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
191 : span(static_cast<pointer>(__arr), _ArrayExtent)
192 { }
193
194 template<typename _Tp, size_t _ArrayExtent>
195 requires __is_compatible_array<_Tp, _ArrayExtent>::value
196 constexpr
197 span(array<_Tp, _ArrayExtent>& __arr) noexcept
198 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
199 { }
200
201 template<typename _Tp, size_t _ArrayExtent>
202 requires __is_compatible_array<const _Tp, _ArrayExtent>::value
203 constexpr
204 span(const array<_Tp, _ArrayExtent>& __arr) noexcept
205 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
206 { }
207
208 template<typename _Range>
209 requires (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
210 && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
211 && (!is_array_v<remove_cvref_t<_Range>>)
212 && ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
213 && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
214 && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
215 constexpr explicit(extent != dynamic_extent)
216 span(_Range&& __range)
217 noexcept(noexcept(ranges::data(__range))
218 && noexcept(ranges::size(__range)))
219 : span(ranges::data(__range), ranges::size(__range))
220 {
221 if constexpr (extent != dynamic_extent)
222 {
223 __glibcxx_assert(ranges::size(__range) == extent);
224 }
225 }
226
227 constexpr
228 span(const span&) noexcept = default;
229
230 template<typename _OType, size_t _OExtent>
231 requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
232 || _Extent == _OExtent)
233 && (__is_array_convertible<_Type, _OType>::value)
234 constexpr
235 explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
236 span(const span<_OType, _OExtent>& __s) noexcept
237 : _M_extent(__s.size()), _M_ptr(__s.data())
238 {
239 if constexpr (extent != dynamic_extent)
240 {
241 __glibcxx_assert(__s.size() == extent);
242 }
243 }
244
245 ~span() noexcept = default;
246
247 constexpr span&
248 operator=(const span&) noexcept = default;
249
250 // observers
251
252 constexpr size_type
253 size() const noexcept
254 { return this->_M_extent._M_extent(); }
255
256 constexpr size_type
257 size_bytes() const noexcept
258 { return this->_M_extent._M_extent() * sizeof(element_type); }
259
260 [[nodiscard]] constexpr bool
261 empty() const noexcept
262 { return size() == 0; }
263
264 // element access
265
266 constexpr reference
267 front() const noexcept
268 {
269 __glibcxx_assert(!empty());
270 return *this->_M_ptr;
271 }
272
273 constexpr reference
274 back() const noexcept
275 {
276 __glibcxx_assert(!empty());
277 return *(this->_M_ptr + (size() - 1));
278 }
279
280 constexpr reference
281 operator[](size_type __idx) const noexcept
282 {
283 __glibcxx_assert(__idx < size());
284 return *(this->_M_ptr + __idx);
285 }
286
287 constexpr pointer
288 data() const noexcept
289 { return this->_M_ptr; }
290
291 // iterator support
292
293 constexpr iterator
294 begin() const noexcept
295 { return iterator(this->_M_ptr); }
296
297 constexpr iterator
298 end() const noexcept
299 { return iterator(this->_M_ptr + this->size()); }
300
301 constexpr reverse_iterator
302 rbegin() const noexcept
303 { return reverse_iterator(this->end()); }
304
305 constexpr reverse_iterator
306 rend() const noexcept
307 { return reverse_iterator(this->begin()); }
308
309 // subviews
310
311 template<size_t _Count>
312 constexpr span<element_type, _Count>
313 first() const noexcept
314 {
315 if constexpr (_Extent == dynamic_extent)
316 __glibcxx_assert(_Count <= size());
317 else
318 static_assert(_Count <= extent);
319 using _Sp = span<element_type, _Count>;
320 return _Sp{ this->data(), _Count };
321 }
322
323 constexpr span<element_type, dynamic_extent>
324 first(size_type __count) const noexcept
325 {
326 __glibcxx_assert(__count <= size());
327 return { this->data(), __count };
328 }
329
330 template<size_t _Count>
331 constexpr span<element_type, _Count>
332 last() const noexcept
333 {
334 if constexpr (_Extent == dynamic_extent)
335 __glibcxx_assert(_Count <= size());
336 else
337 static_assert(_Count <= extent);
338 using _Sp = span<element_type, _Count>;
339 return _Sp{ this->data() + (this->size() - _Count), _Count };
340 }
341
342 constexpr span<element_type, dynamic_extent>
343 last(size_type __count) const noexcept
344 {
345 __glibcxx_assert(__count <= size());
346 return { this->data() + (this->size() - __count), __count };
347 }
348
349 template<size_t _Offset, size_t _Count = dynamic_extent>
350 constexpr auto
351 subspan() const noexcept
352 -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
353 {
354 if constexpr (_Extent == dynamic_extent)
355 {
356 __glibcxx_assert(_Offset <= size());
357 }
358 else
359 static_assert(_Offset <= extent);
360
361 using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
362
363 if constexpr (_Count == dynamic_extent)
364 return _Sp{ this->data() + _Offset, this->size() - _Offset };
365 else
366 {
367 if constexpr (_Extent == dynamic_extent)
368 {
369 __glibcxx_assert(_Count <= size());
370 __glibcxx_assert(_Count <= (size() - _Offset));
371 }
372 else
373 {
374 static_assert(_Count <= extent);
375 static_assert(_Count <= (extent - _Offset));
376 }
377 return _Sp{ this->data() + _Offset, _Count };
378 }
379 }
380
381 constexpr span<element_type, dynamic_extent>
382 subspan(size_type __offset, size_type __count = dynamic_extent) const
383 noexcept
384 {
385 __glibcxx_assert(__offset <= size());
386 if (__count == dynamic_extent)
387 __count = this->size() - __offset;
388 else
389 {
390 __glibcxx_assert(__count <= size());
391 __glibcxx_assert(__offset + __count <= size());
392 }
393 return {this->data() + __offset, __count};
394 }
395
396 private:
397 [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
398 pointer _M_ptr;
399 };
400
401 // deduction guides
402
403 template<typename _Type, size_t _ArrayExtent>
404 span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
405
406 template<typename _Type, size_t _ArrayExtent>
407 span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
408
409 template<typename _Type, size_t _ArrayExtent>
410 span(const array<_Type, _ArrayExtent>&)
411 -> span<const _Type, _ArrayExtent>;
412
413 template<contiguous_iterator _Iter, typename _End>
414 span(_Iter, _End)
415 -> span<remove_reference_t<iter_reference_t<_Iter>>>;
416
417 template<ranges::contiguous_range _Range>
418 span(_Range &&)
419 -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
420
421 template<typename _Type, size_t _Extent>
422 inline
423 span<const byte, _Extent == dynamic_extent
424 ? dynamic_extent : _Extent * sizeof(_Type)>
425 as_bytes(span<_Type, _Extent> __sp) noexcept
426 {
427 auto data = reinterpret_cast<const byte*>(__sp.data());
428 auto size = __sp.size_bytes();
429 constexpr auto extent = _Extent == dynamic_extent
430 ? dynamic_extent : _Extent * sizeof(_Type);
431 return span<const byte, extent>{data, size};
432 }
433
434 template<typename _Type, size_t _Extent>
435 requires (!is_const_v<_Type>)
436 inline
437 span<byte, _Extent == dynamic_extent
438 ? dynamic_extent : _Extent * sizeof(_Type)>
439 as_writable_bytes(span<_Type, _Extent> __sp) noexcept
440 {
441 auto data = reinterpret_cast<byte*>(__sp.data());
442 auto size = __sp.size_bytes();
443 constexpr auto extent = _Extent == dynamic_extent
444 ? dynamic_extent : _Extent * sizeof(_Type);
445 return span<byte, extent>{data, size};
446 }
447
448 namespace ranges
449 {
450 // Opt-in to borrowed_range concept
451 template<typename _ElementType, size_t _Extent>
452 inline constexpr bool
453 enable_borrowed_range<span<_ElementType, _Extent>> = true;
454
455 // Opt-in to view concept
456 template<typename _ElementType, size_t _Extent>
457 inline constexpr bool
458 enable_view<span<_ElementType, _Extent>> = true;
459 }
460_GLIBCXX_END_NAMESPACE_VERSION
461} // namespace std
462#endif // concepts
463#endif // C++20
464#endif // _GLIBCXX_SPAN