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1// -*- C++ -*-
2//===----------------------------------------------------------------------===//
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===---------------------------------------------------------------------===//
9
10#ifndef _LIBCPP_SPAN
11#define _LIBCPP_SPAN
12
13/*
14    span synopsis
15
16namespace std {
17
18// constants
19inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
20
21template<class T>
22  concept integral-constant-like =                           // exposition only, since C++26
23    is_integral_v<decltype(T::value)> &&
24    !is_same_v<bool, remove_const_t<decltype(T::value)>> &&
25    convertible_to<T, decltype(T::value)> &&
26    equality_comparable_with<T, decltype(T::value)> &&
27    bool_constant<T() == T::value>::value &&
28    bool_constant<static_cast<decltype(T::value)>(T()) == T::value>::value;
29
30template<class T>
31  constexpr size_t maybe-static-ext = dynamic_extent;        // exposition only, since C++26
32template<integral-constant-like T>
33  constexpr size_t maybe-static-ext<T> = {T::value};
34
35// [views.span], class template span
36template <class ElementType, size_t Extent = dynamic_extent>
37    class span;
38
39template<class ElementType, size_t Extent>
40  inline constexpr bool ranges::enable_view<span<ElementType, Extent>> = true;
41
42template<class ElementType, size_t Extent>
43    inline constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true;
44
45// [span.objectrep], views of object representation
46template <class ElementType, size_t Extent>
47    span<const byte, ((Extent == dynamic_extent) ? dynamic_extent :
48        (sizeof(ElementType) * Extent))> as_bytes(span<ElementType, Extent> s) noexcept;
49
50template <class ElementType, size_t Extent>
51    span<      byte, ((Extent == dynamic_extent) ? dynamic_extent :
52        (sizeof(ElementType) * Extent))> as_writable_bytes(span<ElementType, Extent> s) noexcept;
53
54
55template <class ElementType, size_t Extent = dynamic_extent>
56class span {
57public:
58    // constants and types
59    using element_type = ElementType;
60    using value_type = remove_cv_t<ElementType>;
61    using size_type = size_t;
62    using difference_type = ptrdiff_t;
63    using pointer = element_type*;
64    using const_pointer = const element_type*;
65    using reference = element_type&;
66    using const_reference = const element_type&;
67    using iterator = implementation-defined;
68    using reverse_iterator = std::reverse_iterator<iterator>;
69    static constexpr size_type extent = Extent;
70
71    // [span.cons], span constructors, copy, assignment, and destructor
72    constexpr span() noexcept;
73    template <class It>
74    constexpr explicit(Extent != dynamic_extent) span(It first, size_type count);
75    template <class It, class End>
76    constexpr explicit(Extent != dynamic_extent) span(It first, End last);
77    template <size_t N>
78        constexpr span(type_identity_t<element_type> (&arr)[N]) noexcept;
79    template <size_t N>
80        constexpr span(array<value_type, N>& arr) noexcept;
81    template <size_t N>
82        constexpr span(const array<value_type, N>& arr) noexcept;
83    template<class R>
84      constexpr explicit(Extent != dynamic_extent) span(R&& r);
85    constexpr explicit(extent != dynamic_extent) span(std::initializer_list<value_type> il); // Since C++26
86    constexpr span(const span& other) noexcept = default;
87    template <class OtherElementType, size_t OtherExtent>
88        constexpr explicit(Extent != dynamic_extent) span(const span<OtherElementType, OtherExtent>& s) noexcept;
89    constexpr span& operator=(const span& other) noexcept = default;
90
91    // [span.sub], span subviews
92    template <size_t Count>
93        constexpr span<element_type, Count> first() const;
94    template <size_t Count>
95        constexpr span<element_type, Count> last() const;
96    template <size_t Offset, size_t Count = dynamic_extent>
97        constexpr span<element_type, see below> subspan() const;
98
99    constexpr span<element_type, dynamic_extent> first(size_type count) const;
100    constexpr span<element_type, dynamic_extent> last(size_type count) const;
101    constexpr span<element_type, dynamic_extent> subspan(size_type offset, size_type count = dynamic_extent) const;
102
103    // [span.obs], span observers
104    constexpr size_type size() const noexcept;
105    constexpr size_type size_bytes() const noexcept;
106    [[nodiscard]] constexpr bool empty() const noexcept;
107
108    // [span.elem], span element access
109    constexpr reference operator[](size_type idx) const;
110    constexpr reference at(size_type idx) const; // since C++26
111    constexpr reference front() const;
112    constexpr reference back() const;
113    constexpr pointer data() const noexcept;
114
115    // [span.iterators], span iterator support
116    constexpr iterator begin() const noexcept;
117    constexpr iterator end() const noexcept;
118    constexpr reverse_iterator rbegin() const noexcept;
119    constexpr reverse_iterator rend() const noexcept;
120
121private:
122    pointer data_;    // exposition only
123    size_type size_;  // exposition only
124};
125
126template<class It, class EndOrSize>
127    span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>;                             // until C++26
128template<class It, class EndOrSize>
129    span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<It>>, maybe-static-ext<EndOrSize>>; // since C++26
130
131template<class T, size_t N>
132    span(T (&)[N]) -> span<T, N>;
133
134template<class T, size_t N>
135    span(array<T, N>&) -> span<T, N>;
136
137template<class T, size_t N>
138    span(const array<T, N>&) -> span<const T, N>;
139
140template<class R>
141    span(R&&) -> span<remove_reference_t<ranges::range_reference_t<R>>>;
142
143} // namespace std
144
145*/
146
147#include <__assert>
148#include <__concepts/convertible_to.h>
149#include <__concepts/equality_comparable.h>
150#include <__config>
151#include <__cstddef/byte.h>
152#include <__cstddef/ptrdiff_t.h>
153#include <__fwd/array.h>
154#include <__fwd/span.h>
155#include <__iterator/bounded_iter.h>
156#include <__iterator/concepts.h>
157#include <__iterator/iterator_traits.h>
158#include <__iterator/reverse_iterator.h>
159#include <__iterator/wrap_iter.h>
160#include <__memory/pointer_traits.h>
161#include <__ranges/concepts.h>
162#include <__ranges/data.h>
163#include <__ranges/enable_borrowed_range.h>
164#include <__ranges/enable_view.h>
165#include <__ranges/size.h>
166#include <__type_traits/integral_constant.h>
167#include <__type_traits/is_array.h>
168#include <__type_traits/is_const.h>
169#include <__type_traits/is_convertible.h>
170#include <__type_traits/is_integral.h>
171#include <__type_traits/is_same.h>
172#include <__type_traits/remove_const.h>
173#include <__type_traits/remove_cv.h>
174#include <__type_traits/remove_cvref.h>
175#include <__type_traits/remove_reference.h>
176#include <__type_traits/type_identity.h>
177#include <__utility/forward.h>
178#include <initializer_list>
179#include <stdexcept>
180#include <version>
181
182// standard-mandated includes
183
184// [iterator.range]
185#include <__iterator/access.h>
186#include <__iterator/data.h>
187#include <__iterator/empty.h>
188#include <__iterator/reverse_access.h>
189#include <__iterator/size.h>
190
191#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
192#  pragma GCC system_header
193#endif
194
195_LIBCPP_PUSH_MACROS
196#include <__undef_macros>
197
198_LIBCPP_BEGIN_NAMESPACE_STD
199
200#if _LIBCPP_STD_VER >= 20
201
202template <class _Tp>
203struct __is_std_span : false_type {};
204
205template <class _Tp, size_t _Sz>
206struct __is_std_span<span<_Tp, _Sz>> : true_type {};
207
208template <class _Range, class _ElementType>
209concept __span_compatible_range =
210    !__is_std_span<remove_cvref_t<_Range>>::value &&                //
211    ranges::contiguous_range<_Range> &&                             //
212    ranges::sized_range<_Range> &&                                  //
213    (ranges::borrowed_range<_Range> || is_const_v<_ElementType>) && //
214    !__is_std_array_v<remove_cvref_t<_Range>> &&                    //
215    !is_array_v<remove_cvref_t<_Range>> &&                          //
216    is_convertible_v<remove_reference_t<ranges::range_reference_t<_Range>> (*)[], _ElementType (*)[]>;
217
218template <class _From, class _To>
219concept __span_array_convertible = is_convertible_v<_From (*)[], _To (*)[]>;
220
221template <class _It, class _Tp>
222concept __span_compatible_iterator =
223    contiguous_iterator<_It> && __span_array_convertible<remove_reference_t<iter_reference_t<_It>>, _Tp>;
224
225template <class _Sentinel, class _It>
226concept __span_compatible_sentinel_for = sized_sentinel_for<_Sentinel, _It> && !is_convertible_v<_Sentinel, size_t>;
227
228template <typename _Tp, size_t _Extent>
229class _LIBCPP_TEMPLATE_VIS span {
230public:
231  //  constants and types
232  using element_type    = _Tp;
233  using value_type      = remove_cv_t<_Tp>;
234  using size_type       = size_t;
235  using difference_type = ptrdiff_t;
236  using pointer         = _Tp*;
237  using const_pointer   = const _Tp*;
238  using reference       = _Tp&;
239  using const_reference = const _Tp&;
240#  ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
241  using iterator = __bounded_iter<pointer>;
242#  else
243  using iterator = __wrap_iter<pointer>;
244#  endif
245  using reverse_iterator = std::reverse_iterator<iterator>;
246
247  static constexpr size_type extent = _Extent;
248
249  // [span.cons], span constructors, copy, assignment, and destructor
250  template <size_t _Sz = _Extent>
251    requires(_Sz == 0)
252  _LIBCPP_HIDE_FROM_ABI constexpr span() noexcept : __data_{nullptr} {}
253
254#  if _LIBCPP_STD_VER >= 26
255  _LIBCPP_HIDE_FROM_ABI constexpr explicit span(std::initializer_list<value_type> __il)
256    requires is_const_v<element_type>
257      : __data_{__il.begin()} {
258    _LIBCPP_ASSERT_VALID_INPUT_RANGE(
259        _Extent == __il.size(), "Size mismatch in span's constructor _Extent != __il.size().");
260  }
261#  endif
262
263  constexpr span(const span&) noexcept            = default;
264  constexpr span& operator=(const span&) noexcept = default;
265
266  template <__span_compatible_iterator<element_type> _It>
267  _LIBCPP_HIDE_FROM_ABI constexpr explicit span(_It __first, size_type __count) : __data_{std::to_address(__first)} {
268    (void)__count;
269    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Extent == __count, "size mismatch in span's constructor (iterator, len)");
270  }
271
272  template <__span_compatible_iterator<element_type> _It, __span_compatible_sentinel_for<_It> _End>
273  _LIBCPP_HIDE_FROM_ABI constexpr explicit span(_It __first, _End __last) : __data_{std::to_address(__first)} {
274    // [span.cons]/10
275    // Throws: When and what last - first throws.
276    [[maybe_unused]] auto __dist = __last - __first;
277    _LIBCPP_ASSERT_VALID_INPUT_RANGE(__dist >= 0, "invalid range in span's constructor (iterator, sentinel)");
278    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
279        __dist == _Extent, "invalid range in span's constructor (iterator, sentinel): last - first != extent");
280  }
281
282  _LIBCPP_HIDE_FROM_ABI constexpr span(type_identity_t<element_type> (&__arr)[_Extent]) noexcept : __data_{__arr} {}
283
284  template <__span_array_convertible<element_type> _OtherElementType>
285  _LIBCPP_HIDE_FROM_ABI constexpr span(array<_OtherElementType, _Extent>& __arr) noexcept : __data_{__arr.data()} {}
286
287  template <class _OtherElementType>
288    requires __span_array_convertible<const _OtherElementType, element_type>
289  _LIBCPP_HIDE_FROM_ABI constexpr span(const array<_OtherElementType, _Extent>& __arr) noexcept
290      : __data_{__arr.data()} {}
291
292  template <__span_compatible_range<element_type> _Range>
293  _LIBCPP_HIDE_FROM_ABI constexpr explicit span(_Range&& __r) : __data_{ranges::data(__r)} {
294    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(ranges::size(__r) == _Extent, "size mismatch in span's constructor (range)");
295  }
296
297  template <__span_array_convertible<element_type> _OtherElementType>
298  _LIBCPP_HIDE_FROM_ABI constexpr span(const span<_OtherElementType, _Extent>& __other) noexcept
299      : __data_{__other.data()} {}
300
301  template <__span_array_convertible<element_type> _OtherElementType>
302  _LIBCPP_HIDE_FROM_ABI constexpr explicit span(const span<_OtherElementType, dynamic_extent>& __other) noexcept
303      : __data_{__other.data()} {
304    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Extent == __other.size(), "size mismatch in span's constructor (other span)");
305  }
306
307  template <size_t _Count>
308  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> first() const noexcept {
309    static_assert(_Count <= _Extent, "span<T, N>::first<Count>(): Count out of range");
310    return span<element_type, _Count>{data(), _Count};
311  }
312
313  template <size_t _Count>
314  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> last() const noexcept {
315    static_assert(_Count <= _Extent, "span<T, N>::last<Count>(): Count out of range");
316    return span<element_type, _Count>{data() + size() - _Count, _Count};
317  }
318
319  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept {
320    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T, N>::first(count): count out of range");
321    return {data(), __count};
322  }
323
324  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> last(size_type __count) const noexcept {
325    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T, N>::last(count): count out of range");
326    return {data() + size() - __count, __count};
327  }
328
329  template <size_t _Offset, size_t _Count = dynamic_extent>
330  _LIBCPP_HIDE_FROM_ABI constexpr auto
331  subspan() const noexcept -> span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset> {
332    static_assert(_Offset <= _Extent, "span<T, N>::subspan<Offset, Count>(): Offset out of range");
333    static_assert(_Count == dynamic_extent || _Count <= _Extent - _Offset,
334                  "span<T, N>::subspan<Offset, Count>(): Offset + Count out of range");
335
336    using _ReturnType = span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset>;
337    return _ReturnType{data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
338  }
339
340  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent>
341  subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept {
342    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__offset <= size(), "span<T, N>::subspan(offset, count): offset out of range");
343    if (__count == dynamic_extent)
344      return {data() + __offset, size() - __offset};
345    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
346        __count <= size() - __offset, "span<T, N>::subspan(offset, count): offset + count out of range");
347    return {data() + __offset, __count};
348  }
349
350  _LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept { return _Extent; }
351  _LIBCPP_HIDE_FROM_ABI constexpr size_type size_bytes() const noexcept { return _Extent * sizeof(element_type); }
352  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const noexcept { return _Extent == 0; }
353
354  _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](size_type __idx) const noexcept {
355    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__idx < size(), "span<T, N>::operator[](index): index out of range");
356    return __data_[__idx];
357  }
358
359#  if _LIBCPP_STD_VER >= 26
360  _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __index) const {
361    if (__index >= size())
362      std::__throw_out_of_range("span");
363    return __data_[__index];
364  }
365#  endif
366
367  _LIBCPP_HIDE_FROM_ABI constexpr reference front() const noexcept {
368    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T, N>::front() on empty span");
369    return __data_[0];
370  }
371
372  _LIBCPP_HIDE_FROM_ABI constexpr reference back() const noexcept {
373    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T, N>::back() on empty span");
374    return __data_[size() - 1];
375  }
376
377  _LIBCPP_HIDE_FROM_ABI constexpr pointer data() const noexcept { return __data_; }
378
379  // [span.iter], span iterator support
380  _LIBCPP_HIDE_FROM_ABI constexpr iterator begin() const noexcept {
381#  ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
382    return std::__make_bounded_iter(data(), data(), data() + size());
383#  else
384    return iterator(data());
385#  endif
386  }
387  _LIBCPP_HIDE_FROM_ABI constexpr iterator end() const noexcept {
388#  ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
389    return std::__make_bounded_iter(data() + size(), data(), data() + size());
390#  else
391    return iterator(data() + size());
392#  endif
393  }
394  _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator(end()); }
395  _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rend() const noexcept { return reverse_iterator(begin()); }
396
397  _LIBCPP_HIDE_FROM_ABI span<const byte, _Extent * sizeof(element_type)> __as_bytes() const noexcept {
398    return span<const byte, _Extent * sizeof(element_type)>{reinterpret_cast<const byte*>(data()), size_bytes()};
399  }
400
401  _LIBCPP_HIDE_FROM_ABI span<byte, _Extent * sizeof(element_type)> __as_writable_bytes() const noexcept {
402    return span<byte, _Extent * sizeof(element_type)>{reinterpret_cast<byte*>(data()), size_bytes()};
403  }
404
405private:
406  pointer __data_;
407};
408
409template <typename _Tp>
410class _LIBCPP_TEMPLATE_VIS span<_Tp, dynamic_extent> {
411public:
412  //  constants and types
413  using element_type    = _Tp;
414  using value_type      = remove_cv_t<_Tp>;
415  using size_type       = size_t;
416  using difference_type = ptrdiff_t;
417  using pointer         = _Tp*;
418  using const_pointer   = const _Tp*;
419  using reference       = _Tp&;
420  using const_reference = const _Tp&;
421#  ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
422  using iterator = __bounded_iter<pointer>;
423#  else
424  using iterator = __wrap_iter<pointer>;
425#  endif
426  using reverse_iterator = std::reverse_iterator<iterator>;
427
428  static constexpr size_type extent = dynamic_extent;
429
430  // [span.cons], span constructors, copy, assignment, and destructor
431  _LIBCPP_HIDE_FROM_ABI constexpr span() noexcept : __data_{nullptr}, __size_{0} {}
432
433#  if _LIBCPP_STD_VER >= 26
434  _LIBCPP_HIDE_FROM_ABI constexpr span(std::initializer_list<value_type> __il)
435    requires is_const_v<element_type>
436      : __data_{__il.begin()}, __size_{__il.size()} {}
437#  endif
438
439  constexpr span(const span&) noexcept            = default;
440  constexpr span& operator=(const span&) noexcept = default;
441
442  template <__span_compatible_iterator<element_type> _It>
443  _LIBCPP_HIDE_FROM_ABI constexpr span(_It __first, size_type __count)
444      : __data_{std::to_address(__first)}, __size_{__count} {}
445
446  template <__span_compatible_iterator<element_type> _It, __span_compatible_sentinel_for<_It> _End>
447  _LIBCPP_HIDE_FROM_ABI constexpr span(_It __first, _End __last)
448      : __data_(std::to_address(__first)), __size_(__last - __first) {
449    _LIBCPP_ASSERT_VALID_INPUT_RANGE(__last - __first >= 0, "invalid range in span's constructor (iterator, sentinel)");
450  }
451
452  template <size_t _Sz>
453  _LIBCPP_HIDE_FROM_ABI constexpr span(type_identity_t<element_type> (&__arr)[_Sz]) noexcept
454      : __data_{__arr}, __size_{_Sz} {}
455
456  template <__span_array_convertible<element_type> _OtherElementType, size_t _Sz>
457  _LIBCPP_HIDE_FROM_ABI constexpr span(array<_OtherElementType, _Sz>& __arr) noexcept
458      : __data_{__arr.data()}, __size_{_Sz} {}
459
460  template <class _OtherElementType, size_t _Sz>
461    requires __span_array_convertible<const _OtherElementType, element_type>
462  _LIBCPP_HIDE_FROM_ABI constexpr span(const array<_OtherElementType, _Sz>& __arr) noexcept
463      : __data_{__arr.data()}, __size_{_Sz} {}
464
465  template <__span_compatible_range<element_type> _Range>
466  _LIBCPP_HIDE_FROM_ABI constexpr span(_Range&& __r) : __data_(ranges::data(__r)), __size_{ranges::size(__r)} {}
467
468  template <__span_array_convertible<element_type> _OtherElementType, size_t _OtherExtent>
469  _LIBCPP_HIDE_FROM_ABI constexpr span(const span<_OtherElementType, _OtherExtent>& __other) noexcept
470      : __data_{__other.data()}, __size_{__other.size()} {}
471
472  template <size_t _Count>
473  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> first() const noexcept {
474    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Count <= size(), "span<T>::first<Count>(): Count out of range");
475    return span<element_type, _Count>{data(), _Count};
476  }
477
478  template <size_t _Count>
479  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> last() const noexcept {
480    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Count <= size(), "span<T>::last<Count>(): Count out of range");
481    return span<element_type, _Count>{data() + size() - _Count, _Count};
482  }
483
484  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept {
485    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T>::first(count): count out of range");
486    return {data(), __count};
487  }
488
489  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> last(size_type __count) const noexcept {
490    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T>::last(count): count out of range");
491    return {data() + size() - __count, __count};
492  }
493
494  template <size_t _Offset, size_t _Count = dynamic_extent>
495  _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> subspan() const noexcept {
496    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Offset <= size(), "span<T>::subspan<Offset, Count>(): Offset out of range");
497    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Count == dynamic_extent || _Count <= size() - _Offset,
498                                        "span<T>::subspan<Offset, Count>(): Offset + Count out of range");
499    return span<element_type, _Count>{data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
500  }
501
502  constexpr span<element_type, dynamic_extent> _LIBCPP_HIDE_FROM_ABI
503  subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept {
504    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__offset <= size(), "span<T>::subspan(offset, count): offset out of range");
505    if (__count == dynamic_extent)
506      return {data() + __offset, size() - __offset};
507    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
508        __count <= size() - __offset, "span<T>::subspan(offset, count): offset + count out of range");
509    return {data() + __offset, __count};
510  }
511
512  _LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept { return __size_; }
513  _LIBCPP_HIDE_FROM_ABI constexpr size_type size_bytes() const noexcept { return __size_ * sizeof(element_type); }
514  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const noexcept { return __size_ == 0; }
515
516  _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](size_type __idx) const noexcept {
517    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__idx < size(), "span<T>::operator[](index): index out of range");
518    return __data_[__idx];
519  }
520
521#  if _LIBCPP_STD_VER >= 26
522  _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __index) const {
523    if (__index >= size())
524      std::__throw_out_of_range("span");
525    return __data_[__index];
526  }
527#  endif
528
529  _LIBCPP_HIDE_FROM_ABI constexpr reference front() const noexcept {
530    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T>::front() on empty span");
531    return __data_[0];
532  }
533
534  _LIBCPP_HIDE_FROM_ABI constexpr reference back() const noexcept {
535    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T>::back() on empty span");
536    return __data_[size() - 1];
537  }
538
539  _LIBCPP_HIDE_FROM_ABI constexpr pointer data() const noexcept { return __data_; }
540
541  // [span.iter], span iterator support
542  _LIBCPP_HIDE_FROM_ABI constexpr iterator begin() const noexcept {
543#  ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
544    return std::__make_bounded_iter(data(), data(), data() + size());
545#  else
546    return iterator(data());
547#  endif
548  }
549  _LIBCPP_HIDE_FROM_ABI constexpr iterator end() const noexcept {
550#  ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
551    return std::__make_bounded_iter(data() + size(), data(), data() + size());
552#  else
553    return iterator(data() + size());
554#  endif
555  }
556  _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator(end()); }
557  _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rend() const noexcept { return reverse_iterator(begin()); }
558
559  _LIBCPP_HIDE_FROM_ABI span<const byte, dynamic_extent> __as_bytes() const noexcept {
560    return {reinterpret_cast<const byte*>(data()), size_bytes()};
561  }
562
563  _LIBCPP_HIDE_FROM_ABI span<byte, dynamic_extent> __as_writable_bytes() const noexcept {
564    return {reinterpret_cast<byte*>(data()), size_bytes()};
565  }
566
567private:
568  pointer __data_;
569  size_type __size_;
570};
571
572template <class _Tp, size_t _Extent>
573inline constexpr bool ranges::enable_borrowed_range<span<_Tp, _Extent> > = true;
574
575template <class _ElementType, size_t _Extent>
576inline constexpr bool ranges::enable_view<span<_ElementType, _Extent>> = true;
577
578//  as_bytes & as_writable_bytes
579template <class _Tp, size_t _Extent>
580_LIBCPP_HIDE_FROM_ABI auto as_bytes(span<_Tp, _Extent> __s) noexcept {
581  return __s.__as_bytes();
582}
583
584template <class _Tp, size_t _Extent>
585  requires(!is_const_v<_Tp>)
586_LIBCPP_HIDE_FROM_ABI auto as_writable_bytes(span<_Tp, _Extent> __s) noexcept {
587  return __s.__as_writable_bytes();
588}
589
590#  if _LIBCPP_STD_VER >= 26
591template <class _Tp>
592concept __integral_constant_like =
593    is_integral_v<decltype(_Tp::value)> && !is_same_v<bool, remove_const_t<decltype(_Tp::value)>> &&
594    convertible_to<_Tp, decltype(_Tp::value)> && equality_comparable_with<_Tp, decltype(_Tp::value)> &&
595    bool_constant<_Tp() == _Tp::value>::value &&
596    bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>::value;
597
598template <class _Tp>
599inline constexpr size_t __maybe_static_ext = dynamic_extent;
600
601template <__integral_constant_like _Tp>
602inline constexpr size_t __maybe_static_ext<_Tp> = {_Tp::value};
603
604template <contiguous_iterator _It, class _EndOrSize>
605span(_It, _EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>, __maybe_static_ext<_EndOrSize>>;
606#  else
607template <contiguous_iterator _It, class _EndOrSize>
608span(_It, _EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>;
609#  endif
610
611template <class _Tp, size_t _Sz>
612span(_Tp (&)[_Sz]) -> span<_Tp, _Sz>;
613
614template <class _Tp, size_t _Sz>
615span(array<_Tp, _Sz>&) -> span<_Tp, _Sz>;
616
617template <class _Tp, size_t _Sz>
618span(const array<_Tp, _Sz>&) -> span<const _Tp, _Sz>;
619
620template <ranges::contiguous_range _Range>
621span(_Range&&) -> span<remove_reference_t<ranges::range_reference_t<_Range>>>;
622
623#endif // _LIBCPP_STD_VER >= 20
624
625_LIBCPP_END_NAMESPACE_STD
626
627_LIBCPP_POP_MACROS
628
629#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
630#  include <array>
631#  include <concepts>
632#  include <functional>
633#  include <iterator>
634#  include <type_traits>
635#endif
636
637#endif // _LIBCPP_SPAN
638