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
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<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
459