libstdc++
span
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1 // Components for manipulating non-owning sequences of objects -*- C++ -*-
2 
3 // Copyright (C) 2019-2021 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 <array>
42 #include <cstddef>
43 #include <bits/stl_iterator.h>
44 #include <bits/ranges_base.h>
45 
46 #if __cpp_lib_concepts
47 namespace 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<std::array<_Tp, _Num>> : true_type { };
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  public:
129  // member types
130  using element_type = _Type;
131  using value_type = remove_cv_t<_Type>;
132  using size_type = size_t;
133  using difference_type = ptrdiff_t;
134  using pointer = _Type*;
135  using const_pointer = const _Type*;
136  using reference = element_type&;
137  using const_reference = const element_type&;
138  using iterator = __gnu_cxx::__normal_iterator<pointer, span>;
139  using reverse_iterator = std::reverse_iterator<iterator>;
140 
141  // member constants
142  static constexpr size_t extent = _Extent;
143 
144  // constructors, copy and assignment
145 
146  constexpr
147  span() noexcept
148  requires ((_Extent + 1u) <= 1u)
149  : _M_ptr(nullptr), _M_extent(0)
150  { }
151 
152  template<contiguous_iterator _It>
153  requires __is_compatible_ref<iter_reference_t<_It>>::value
154  constexpr explicit(extent != dynamic_extent)
155  span(_It __first, size_type __count)
156  noexcept
157  : _M_ptr(std::to_address(__first)), _M_extent(__count)
158  {
159  if constexpr (_Extent != dynamic_extent)
160  {
161  __glibcxx_assert(__count == _Extent);
162  }
163  }
164 
165  template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
166  requires __is_compatible_ref<iter_reference_t<_It>>::value
167  && (!is_convertible_v<_End, size_type>)
168  constexpr explicit(extent != dynamic_extent)
169  span(_It __first, _End __last)
170  noexcept(noexcept(__last - __first))
171  : _M_ptr(std::to_address(__first)),
172  _M_extent(static_cast<size_type>(__last - __first))
173  {
174  if constexpr (_Extent != dynamic_extent)
175  {
176  __glibcxx_assert((__last - __first) == _Extent);
177  }
178  }
179 
180  template<size_t _ArrayExtent>
181  requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
182  constexpr
183  span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
184  : span(static_cast<pointer>(__arr), _ArrayExtent)
185  { }
186 
187  template<typename _Tp, size_t _ArrayExtent>
188  requires __is_compatible_array<_Tp, _ArrayExtent>::value
189  constexpr
190  span(array<_Tp, _ArrayExtent>& __arr) noexcept
191  : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
192  { }
193 
194  template<typename _Tp, size_t _ArrayExtent>
195  requires __is_compatible_array<const _Tp, _ArrayExtent>::value
196  constexpr
197  span(const array<_Tp, _ArrayExtent>& __arr) noexcept
198  : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
199  { }
200 
201  template<typename _Range>
202  requires ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
203  && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
204  && (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
205  && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
206  && (!is_array_v<remove_cvref_t<_Range>>)
207  && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
208  constexpr explicit(extent != dynamic_extent)
209  span(_Range&& __range)
210  noexcept(noexcept(ranges::data(__range))
211  && noexcept(ranges::size(__range)))
212  : span(ranges::data(__range), ranges::size(__range))
213  {
214  if constexpr (extent != dynamic_extent)
215  {
216  __glibcxx_assert(ranges::size(__range) == extent);
217  }
218  }
219 
220  constexpr
221  span(const span&) noexcept = default;
222 
223  template<typename _OType, size_t _OExtent>
224  requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
225  || _Extent == _OExtent)
226  && (__is_array_convertible<_Type, _OType>::value)
227  constexpr
228  explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
229  span(const span<_OType, _OExtent>& __s) noexcept
230  : _M_extent(__s.size()), _M_ptr(__s.data())
231  {
232  if constexpr (extent != dynamic_extent)
233  {
234  __glibcxx_assert(__s.size() == extent);
235  }
236  }
237 
238  ~span() noexcept = default;
239 
240  constexpr span&
241  operator=(const span&) noexcept = default;
242 
243  // observers
244 
245  constexpr size_type
246  size() const noexcept
247  { return this->_M_extent._M_extent(); }
248 
249  constexpr size_type
250  size_bytes() const noexcept
251  { return this->_M_extent._M_extent() * sizeof(element_type); }
252 
253  [[nodiscard]] constexpr bool
254  empty() const noexcept
255  { return size() == 0; }
256 
257  // element access
258 
259  constexpr reference
260  front() const noexcept
261  {
262  __glibcxx_assert(!empty());
263  return *this->_M_ptr;
264  }
265 
266  constexpr reference
267  back() const noexcept
268  {
269  __glibcxx_assert(!empty());
270  return *(this->_M_ptr + (size() - 1));
271  }
272 
273  constexpr reference
274  operator[](size_type __idx) const noexcept
275  {
276  __glibcxx_assert(__idx < size());
277  return *(this->_M_ptr + __idx);
278  }
279 
280  constexpr pointer
281  data() const noexcept
282  { return this->_M_ptr; }
283 
284  // iterator support
285 
286  constexpr iterator
287  begin() const noexcept
288  { return iterator(this->_M_ptr); }
289 
290  constexpr iterator
291  end() const noexcept
292  { return iterator(this->_M_ptr + this->size()); }
293 
294  constexpr reverse_iterator
295  rbegin() const noexcept
296  { return reverse_iterator(this->end()); }
297 
298  constexpr reverse_iterator
299  rend() const noexcept
300  { return reverse_iterator(this->begin()); }
301 
302  // subviews
303 
304  template<size_t _Count>
305  constexpr span<element_type, _Count>
306  first() const noexcept
307  {
308  if constexpr (_Extent == dynamic_extent)
309  __glibcxx_assert(_Count <= size());
310  else
311  static_assert(_Count <= extent);
312  using _Sp = span<element_type, _Count>;
313  return _Sp{ this->data(), _Count };
314  }
315 
316  constexpr span<element_type, dynamic_extent>
317  first(size_type __count) const noexcept
318  {
319  __glibcxx_assert(__count <= size());
320  return { this->data(), __count };
321  }
322 
323  template<size_t _Count>
324  constexpr span<element_type, _Count>
325  last() const noexcept
326  {
327  if constexpr (_Extent == dynamic_extent)
328  __glibcxx_assert(_Count <= size());
329  else
330  static_assert(_Count <= extent);
331  using _Sp = span<element_type, _Count>;
332  return _Sp{ this->data() + (this->size() - _Count), _Count };
333  }
334 
335  constexpr span<element_type, dynamic_extent>
336  last(size_type __count) const noexcept
337  {
338  __glibcxx_assert(__count <= size());
339  return { this->data() + (this->size() - __count), __count };
340  }
341 
342  template<size_t _Offset, size_t _Count = dynamic_extent>
343  constexpr auto
344  subspan() const noexcept
345  -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
346  {
347  if constexpr (_Extent == dynamic_extent)
348  {
349  __glibcxx_assert(_Offset <= size());
350  }
351  else
352  static_assert(_Offset <= extent);
353 
354  using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
355 
356  if constexpr (_Count == dynamic_extent)
357  return _Sp{ this->data() + _Offset, this->size() - _Offset };
358  else
359  {
360  if constexpr (_Extent == dynamic_extent)
361  {
362  __glibcxx_assert(_Count <= size());
363  __glibcxx_assert(_Count <= (size() - _Offset));
364  }
365  else
366  {
367  static_assert(_Count <= extent);
368  static_assert(_Count <= (extent - _Offset));
369  }
370  return _Sp{ this->data() + _Offset, _Count };
371  }
372  }
373 
374  constexpr span<element_type, dynamic_extent>
375  subspan(size_type __offset, size_type __count = dynamic_extent) const
376  noexcept
377  {
378  __glibcxx_assert(__offset <= size());
379  if (__count == dynamic_extent)
380  __count = this->size() - __offset;
381  else
382  {
383  __glibcxx_assert(__count <= size());
384  __glibcxx_assert(__offset + __count <= size());
385  }
386  return {this->data() + __offset, __count};
387  }
388 
389  private:
390  pointer _M_ptr;
391  [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
392  };
393 
394  // deduction guides
395 
396  template<typename _Type, size_t _ArrayExtent>
397  span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
398 
399  template<typename _Type, size_t _ArrayExtent>
400  span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
401 
402  template<typename _Type, size_t _ArrayExtent>
403  span(const array<_Type, _ArrayExtent>&)
404  -> span<const _Type, _ArrayExtent>;
405 
406  template<contiguous_iterator _Iter, typename _End>
407  span(_Iter, _End)
408  -> span<remove_reference_t<iter_reference_t<_Iter>>>;
409 
410  template<typename _Range>
411  span(_Range &&)
412  -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
413 
414  template<typename _Type, size_t _Extent>
415  inline
416  span<const byte, _Extent == dynamic_extent
417  ? dynamic_extent : _Extent * sizeof(_Type)>
418  as_bytes(span<_Type, _Extent> __sp) noexcept
419  {
420  auto data = reinterpret_cast<const byte*>(__sp.data());
421  auto size = __sp.size_bytes();
422  constexpr auto extent = _Extent == dynamic_extent
423  ? dynamic_extent : _Extent * sizeof(_Type);
424  return span<const byte, extent>{data, size};
425  }
426 
427  template<typename _Type, size_t _Extent>
428  requires (!is_const_v<_Type>)
429  inline
430  span<byte, _Extent == dynamic_extent
431  ? dynamic_extent : _Extent * sizeof(_Type)>
432  as_writable_bytes(span<_Type, _Extent> __sp) noexcept
433  {
434  auto data = reinterpret_cast<byte*>(__sp.data());
435  auto size = __sp.size_bytes();
436  constexpr auto extent = _Extent == dynamic_extent
437  ? dynamic_extent : _Extent * sizeof(_Type);
438  return span<byte, extent>{data, size};
439  }
440 
441  namespace ranges
442  {
443  // Opt-in to borrowed_range concept
444  template<typename _ElementType, size_t _Extent>
445  inline constexpr bool
446  enable_borrowed_range<span<_ElementType, _Extent>> = true;
447 
448  // Opt-in to view concept
449  template<typename _ElementType, size_t _Extent>
450  inline constexpr bool
451  enable_view<span<_ElementType, _Extent>>
452  = _Extent == 0 || _Extent == dynamic_extent;
453  }
454 _GLIBCXX_END_NAMESPACE_VERSION
455 } // namespace std
456 #endif // concepts
457 #endif // C++20
458 #endif // _GLIBCXX_SPAN