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 }
169
170 template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
171 requires __is_compatible_ref<iter_reference_t<_It>>::value
172 && (!is_convertible_v<_End, size_type>)
173 constexpr explicit(extent != dynamic_extent)
174 span(_It __first, _End __last)
175 noexcept(noexcept(__last - __first))
176 : _M_extent(static_cast<size_type>(__last - __first)),
177 _M_ptr(std::to_address(__first))
178 {
179 if constexpr (_Extent != dynamic_extent)
180 {
181 __glibcxx_assert((__last - __first) == _Extent);
182 }
183 }
184
185 template<size_t _ArrayExtent>
186 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
187 constexpr
188 span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
189 : span(static_cast<pointer>(__arr), _ArrayExtent)
190 { }
191
192 template<typename _Tp, size_t _ArrayExtent>
193 requires __is_compatible_array<_Tp, _ArrayExtent>::value
194 constexpr
195 span(array<_Tp, _ArrayExtent>& __arr) noexcept
196 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
197 { }
198
199 template<typename _Tp, size_t _ArrayExtent>
200 requires __is_compatible_array<const _Tp, _ArrayExtent>::value
201 constexpr
202 span(const array<_Tp, _ArrayExtent>& __arr) noexcept
203 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
204 { }
205
206 template<typename _Range>
207 requires ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
208 && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
209 && (!__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 && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
213 constexpr explicit(extent != dynamic_extent)
214 span(_Range&& __range)
215 noexcept(noexcept(ranges::data(__range))
216 && noexcept(ranges::size(__range)))
217 : span(ranges::data(__range), ranges::size(__range))
218 {
219 if constexpr (extent != dynamic_extent)
220 {
221 __glibcxx_assert(ranges::size(__range) == extent);
222 }
223 }
224
225 constexpr
226 span(const span&) noexcept = default;
227
228 template<typename _OType, size_t _OExtent>
229 requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
230 || _Extent == _OExtent)
231 && (__is_array_convertible<_Type, _OType>::value)
232 constexpr
233 explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
234 span(const span<_OType, _OExtent>& __s) noexcept
235 : _M_extent(__s.size()), _M_ptr(__s.data())
236 {
237 if constexpr (extent != dynamic_extent)
238 {
239 __glibcxx_assert(__s.size() == extent);
240 }
241 }
242
243 ~span() noexcept = default;
244
245 constexpr span&
246 operator=(const span&) noexcept = default;
247
248 // observers
249
250 constexpr size_type
251 size() const noexcept
252 { return this->_M_extent._M_extent(); }
253
254 constexpr size_type
255 size_bytes() const noexcept
256 { return this->_M_extent._M_extent() * sizeof(element_type); }
257
258 [[nodiscard]] constexpr bool
259 empty() const noexcept
260 { return size() == 0; }
261
262 // element access
263
264 constexpr reference
265 front() const noexcept
266 {
267 static_assert(extent != 0);
268 __glibcxx_assert(!empty());
269 return *this->_M_ptr;
270 }
271
272 constexpr reference
273 back() const noexcept
274 {
275 static_assert(extent != 0);
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 static_assert(extent != 0);
284 __glibcxx_assert(__idx < size());
285 return *(this->_M_ptr + __idx);
286 }
287
288 constexpr pointer
289 data() const noexcept
290 { return this->_M_ptr; }
291
292 // iterator support
293
294 constexpr iterator
295 begin() const noexcept
296 { return iterator(this->_M_ptr); }
297
298 constexpr iterator
299 end() const noexcept
300 { return iterator(this->_M_ptr + this->size()); }
301
302 constexpr reverse_iterator
303 rbegin() const noexcept
304 { return reverse_iterator(this->end()); }
305
306 constexpr reverse_iterator
307 rend() const noexcept
308 { return reverse_iterator(this->begin()); }
309
310 // subviews
311
312 template<size_t _Count>
313 constexpr span<element_type, _Count>
314 first() const noexcept
315 {
316 if constexpr (_Extent == dynamic_extent)
317 __glibcxx_assert(_Count <= size());
318 else
319 static_assert(_Count <= extent);
320 using _Sp = span<element_type, _Count>;
321 return _Sp{ this->data(), _Count };
322 }
323
324 constexpr span<element_type, dynamic_extent>
325 first(size_type __count) const noexcept
326 {
327 __glibcxx_assert(__count <= size());
328 return { this->data(), __count };
329 }
330
331 template<size_t _Count>
332 constexpr span<element_type, _Count>
333 last() const noexcept
334 {
335 if constexpr (_Extent == dynamic_extent)
336 __glibcxx_assert(_Count <= size());
337 else
338 static_assert(_Count <= extent);
339 using _Sp = span<element_type, _Count>;
340 return _Sp{ this->data() + (this->size() - _Count), _Count };
341 }
342
343 constexpr span<element_type, dynamic_extent>
344 last(size_type __count) const noexcept
345 {
346 __glibcxx_assert(__count <= size());
347 return { this->data() + (this->size() - __count), __count };
348 }
349
350 template<size_t _Offset, size_t _Count = dynamic_extent>
351 constexpr auto
352 subspan() const noexcept
353 -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
354 {
355 if constexpr (_Extent == dynamic_extent)
356 {
357 __glibcxx_assert(_Offset <= size());
358 }
359 else
360 static_assert(_Offset <= extent);
361
362 using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
363
364 if constexpr (_Count == dynamic_extent)
365 return _Sp{ this->data() + _Offset, this->size() - _Offset };
366 else
367 {
368 if constexpr (_Extent == dynamic_extent)
369 {
370 __glibcxx_assert(_Count <= size());
371 __glibcxx_assert(_Count <= (size() - _Offset));
372 }
373 else
374 {
375 static_assert(_Count <= extent);
376 static_assert(_Count <= (extent - _Offset));
377 }
378 return _Sp{ this->data() + _Offset, _Count };
379 }
380 }
381
382 constexpr span<element_type, dynamic_extent>
383 subspan(size_type __offset, size_type __count = dynamic_extent) const
384 noexcept
385 {
386 __glibcxx_assert(__offset <= size());
387 if (__count == dynamic_extent)
388 __count = this->size() - __offset;
389 else
390 {
391 __glibcxx_assert(__count <= size());
392 __glibcxx_assert(__offset + __count <= size());
393 }
394 return {this->data() + __offset, __count};
395 }
396
397 private:
398 [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
399 pointer _M_ptr;
400 };
401
402 // deduction guides
403
404 template<typename _Type, size_t _ArrayExtent>
405 span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
406
407 template<typename _Type, size_t _ArrayExtent>
408 span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
409
410 template<typename _Type, size_t _ArrayExtent>
411 span(const array<_Type, _ArrayExtent>&)
412 -> span<const _Type, _ArrayExtent>;
413
414 template<contiguous_iterator _Iter, typename _End>
415 span(_Iter, _End)
416 -> span<remove_reference_t<iter_reference_t<_Iter>>>;
417
418 template<typename _Range>
419 span(_Range &&)
420 -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
421
422 template<typename _Type, size_t _Extent>
423 inline
424 span<const byte, _Extent == dynamic_extent
425 ? dynamic_extent : _Extent * sizeof(_Type)>
426 as_bytes(span<_Type, _Extent> __sp) noexcept
427 {
428 auto data = reinterpret_cast<const byte*>(__sp.data());
429 auto size = __sp.size_bytes();
430 constexpr auto extent = _Extent == dynamic_extent
431 ? dynamic_extent : _Extent * sizeof(_Type);
432 return span<const byte, extent>{data, size};
433 }
434
435 template<typename _Type, size_t _Extent>
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>>
459 = _Extent == 0 || _Extent == dynamic_extent;
460 }
461_GLIBCXX_END_NAMESPACE_VERSION
462} // namespace std
463#endif // concepts
464#endif // C++20
465#endif // _GLIBCXX_SPAN
integral_constant< bool, true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:75
integral_constant< bool, false > false_type
The type used as a compile-time boolean with false value.
Definition: type_traits:78
_Tp * begin(valarray< _Tp > &__va)
Return an iterator pointing to the first element of the valarray.
Definition: valarray:1214
_Tp * end(valarray< _Tp > &__va)
Return an iterator pointing to one past the last element of the valarray.
Definition: valarray:1234
ISO C++ entities toplevel namespace is std.
constexpr auto rend(_Container &__cont) -> decltype(__cont.rend())
Return a reverse iterator pointing one past the first element of the container.
Definition: range_access.h:161
constexpr auto rbegin(_Container &__cont) -> decltype(__cont.rbegin())
Return a reverse iterator pointing to the last element of the container.
Definition: range_access.h:141