v1/__mdspan/extents.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //                        Kokkos v. 4.0
0009 //       Copyright (2022) National Technology & Engineering
0010 //               Solutions of Sandia, LLC (NTESS).
0011 //
0012 // Under the terms of Contract DE-NA0003525 with NTESS,
0013 // the U.S. Government retains certain rights in this software.
0014 //
0015 //===---------------------------------------------------------------------===//
0016
0017 #ifndef _LIBCPP___MDSPAN_EXTENTS_H
0018 #define _LIBCPP___MDSPAN_EXTENTS_H
0019
0020 #include <__assert>
0021 #include <__config>
0022
0023 #include <__concepts/arithmetic.h>
0024 #include <__cstddef/byte.h>
0025 #include <__type_traits/common_type.h>
0026 #include <__type_traits/is_convertible.h>
0027 #include <__type_traits/is_nothrow_constructible.h>
0028 #include <__type_traits/is_same.h>
0029 #include <__type_traits/make_unsigned.h>
0030 #include <__utility/integer_sequence.h>
0031 #include <__utility/unreachable.h>
0032 #include <array>
0033 #include <concepts>
0034 #include <limits>
0035 #include <span>
0036
0037 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0038 #  pragma GCC system_header
0039 #endif
0040
0041 _LIBCPP_PUSH_MACROS
0042 #include <__undef_macros>
0043
0044 _LIBCPP_BEGIN_NAMESPACE_STD
0045
0046 #if _LIBCPP_STD_VER >= 23
0047
0048 namespace __mdspan_detail {
0049
0050 // ------------------------------------------------------------------
0051 // ------------ __static_array --------------------------------------
0052 // ------------------------------------------------------------------
0053 // array like class which provides an array of static values with get
0054 template <class _Tp, _Tp... _Values>
0055 struct __static_array {
0056   static constexpr array<_Tp, sizeof...(_Values)> __array = {_Values...};
0057
0058 public:
0059   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __size() { return sizeof...(_Values); }
0060   _LIBCPP_HIDE_FROM_ABI static constexpr _Tp __get(size_t __index) noexcept { return __array[__index]; }
0061
0062   template <size_t _Index>
0063   _LIBCPP_HIDE_FROM_ABI static constexpr _Tp __get() {
0064     return __get(_Index);
0065   }
0066 };
0067
0068 // ------------------------------------------------------------------
0069 // ------------ __possibly_empty_array  -----------------------------
0070 // ------------------------------------------------------------------
0071
0072 // array like class which provides get function and operator [], and
0073 // has a specialization for the size 0 case.
0074 // This is needed to make the __maybe_static_array be truly empty, for
0075 // all static values.
0076
0077 template <class _Tp, size_t _Size>
0078 struct __possibly_empty_array {
0079   _Tp __vals_[_Size];
0080   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& operator[](size_t __index) { return __vals_[__index]; }
0081   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator[](size_t __index) const { return __vals_[__index]; }
0082 };
0083
0084 template <class _Tp>
0085 struct __possibly_empty_array<_Tp, 0> {
0086   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& operator[](size_t) { __libcpp_unreachable(); }
0087   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator[](size_t) const { __libcpp_unreachable(); }
0088 };
0089
0090 // ------------------------------------------------------------------
0091 // ------------ static_partial_sums ---------------------------------
0092 // ------------------------------------------------------------------
0093
0094 // Provides a compile time partial sum one can index into
0095
0096 template <size_t... _Values>
0097 struct __static_partial_sums {
0098   _LIBCPP_HIDE_FROM_ABI static constexpr array<size_t, sizeof...(_Values)> __static_partial_sums_impl() {
0099     array<size_t, sizeof...(_Values)> __values{_Values...};
0100     array<size_t, sizeof...(_Values)> __partial_sums{{}};
0101     size_t __running_sum = 0;
0102     for (int __i = 0; __i != sizeof...(_Values); ++__i) {
0103       __partial_sums[__i] = __running_sum;
0104       __running_sum += __values[__i];
0105     }
0106     return __partial_sums;
0107   }
0108   static constexpr array<size_t, sizeof...(_Values)> __result{__static_partial_sums_impl()};
0109
0110   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __get(size_t __index) { return __result[__index]; }
0111 };
0112
0113 // ------------------------------------------------------------------
0114 // ------------ __maybe_static_array --------------------------------
0115 // ------------------------------------------------------------------
0116
0117 // array like class which has a mix of static and runtime values but
0118 // only stores the runtime values.
0119 // The type of the static and the runtime values can be different.
0120 // The position of a dynamic value is indicated through a tag value.
0121 template <class _TDynamic, class _TStatic, _TStatic _DynTag, _TStatic... _Values>
0122 struct __maybe_static_array {
0123   static_assert(is_convertible<_TStatic, _TDynamic>::value,
0124                 "__maybe_static_array: _TStatic must be convertible to _TDynamic");
0125   static_assert(is_convertible<_TDynamic, _TStatic>::value,
0126                 "__maybe_static_array: _TDynamic must be convertible to _TStatic");
0127
0128 private:
0129   // Static values member
0130   static constexpr size_t __size_         = sizeof...(_Values);
0131   static constexpr size_t __size_dynamic_ = ((_Values == _DynTag) + ... + 0);
0132   using _StaticValues _LIBCPP_NODEBUG     = __static_array<_TStatic, _Values...>;
0133   using _DynamicValues _LIBCPP_NODEBUG    = __possibly_empty_array<_TDynamic, __size_dynamic_>;
0134
0135   // Dynamic values member
0136   _LIBCPP_NO_UNIQUE_ADDRESS _DynamicValues __dyn_vals_;
0137
0138   // static mapping of indices to the position in the dynamic values array
0139   using _DynamicIdxMap _LIBCPP_NODEBUG = __static_partial_sums<static_cast<size_t>(_Values == _DynTag)...>;
0140
0141   template <size_t... _Indices>
0142   _LIBCPP_HIDE_FROM_ABI static constexpr _DynamicValues __zeros(index_sequence<_Indices...>) noexcept {
0143     return _DynamicValues{((void)_Indices, 0)...};
0144   }
0145
0146 public:
0147   _LIBCPP_HIDE_FROM_ABI constexpr __maybe_static_array() noexcept
0148       : __dyn_vals_{__zeros(make_index_sequence<__size_dynamic_>())} {}
0149
0150   // constructors from dynamic values only -- this covers the case for rank() == 0
0151   template <class... _DynVals>
0152     requires(sizeof...(_DynVals) == __size_dynamic_)
0153   _LIBCPP_HIDE_FROM_ABI constexpr __maybe_static_array(_DynVals... __vals)
0154       : __dyn_vals_{static_cast<_TDynamic>(__vals)...} {}
0155
0156   template <class _Tp, size_t _Size >
0157     requires(_Size == __size_dynamic_)
0158   _LIBCPP_HIDE_FROM_ABI constexpr __maybe_static_array([[maybe_unused]] const span<_Tp, _Size>& __vals) {
0159     if constexpr (_Size > 0) {
0160       for (size_t __i = 0; __i < _Size; __i++)
0161         __dyn_vals_[__i] = static_cast<_TDynamic>(__vals[__i]);
0162     }
0163   }
0164
0165   // constructors from all values -- here rank will be greater than 0
0166   template <class... _DynVals>
0167     requires(sizeof...(_DynVals) != __size_dynamic_)
0168   _LIBCPP_HIDE_FROM_ABI constexpr __maybe_static_array(_DynVals... __vals) {
0169     static_assert(sizeof...(_DynVals) == __size_, "Invalid number of values.");
0170     _TDynamic __values[__size_] = {static_cast<_TDynamic>(__vals)...};
0171     for (size_t __i = 0; __i < __size_; __i++) {
0172       _TStatic __static_val = _StaticValues::__get(__i);
0173       if (__static_val == _DynTag) {
0174         __dyn_vals_[_DynamicIdxMap::__get(__i)] = __values[__i];
0175       } else
0176         // Not catching this could lead to out of bounds errors later
0177         // e.g. using my_mdspan_t = mdspan<int, extents<int, 10>>; my_mdspan_t = m(new int[5], 5);
0178         // Right-hand-side construction looks ok with allocation and size matching,
0179         // but since (potentially elsewhere defined) my_mdspan_t has static size m now thinks its range is 10 not 5
0180         _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0181             __values[__i] == static_cast<_TDynamic>(__static_val),
0182             "extents construction: mismatch of provided arguments with static extents.");
0183     }
0184   }
0185
0186   template <class _Tp, size_t _Size>
0187     requires(_Size != __size_dynamic_)
0188   _LIBCPP_HIDE_FROM_ABI constexpr __maybe_static_array(const span<_Tp, _Size>& __vals) {
0189     static_assert(_Size == __size_ || __size_ == dynamic_extent);
0190     for (size_t __i = 0; __i < __size_; __i++) {
0191       _TStatic __static_val = _StaticValues::__get(__i);
0192       if (__static_val == _DynTag) {
0193         __dyn_vals_[_DynamicIdxMap::__get(__i)] = static_cast<_TDynamic>(__vals[__i]);
0194       } else
0195         // Not catching this could lead to out of bounds errors later
0196         // e.g. using my_mdspan_t = mdspan<int, extents<int, 10>>; my_mdspan_t = m(new int[N], span<int,1>(&N));
0197         // Right-hand-side construction looks ok with allocation and size matching,
0198         // but since (potentially elsewhere defined) my_mdspan_t has static size m now thinks its range is 10 not N
0199         _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0200             static_cast<_TDynamic>(__vals[__i]) == static_cast<_TDynamic>(__static_val),
0201             "extents construction: mismatch of provided arguments with static extents.");
0202     }
0203   }
0204
0205   // access functions
0206   _LIBCPP_HIDE_FROM_ABI static constexpr _TStatic __static_value(size_t __i) noexcept {
0207     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__i < __size_, "extents access: index must be less than rank");
0208     return _StaticValues::__get(__i);
0209   }
0210
0211   _LIBCPP_HIDE_FROM_ABI constexpr _TDynamic __value(size_t __i) const {
0212     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__i < __size_, "extents access: index must be less than rank");
0213     _TStatic __static_val = _StaticValues::__get(__i);
0214     return __static_val == _DynTag ? __dyn_vals_[_DynamicIdxMap::__get(__i)] : static_cast<_TDynamic>(__static_val);
0215   }
0216   _LIBCPP_HIDE_FROM_ABI constexpr _TDynamic operator[](size_t __i) const {
0217     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__i < __size_, "extents access: index must be less than rank");
0218     return __value(__i);
0219   }
0220
0221   // observers
0222   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __size() { return __size_; }
0223   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __size_dynamic() { return __size_dynamic_; }
0224 };
0225
0226 // Function to check whether a value is representable as another type
0227 // value must be a positive integer otherwise returns false
0228 // if _From is not an integral, we just check positivity
0229 template <integral _To, class _From>
0230   requires(integral<_From>)
0231 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_representable_as(_From __value) {
0232   using _To_u   = make_unsigned_t<_To>;
0233   using _From_u = make_unsigned_t<_From>;
0234   if constexpr (is_signed_v<_From>) {
0235     if (__value < 0)
0236       return false;
0237   }
0238   if constexpr (static_cast<_To_u>(numeric_limits<_To>::max()) >= static_cast<_From_u>(numeric_limits<_From>::max())) {
0239     return true;
0240   } else {
0241     return static_cast<_To_u>(numeric_limits<_To>::max()) >= static_cast<_From_u>(__value);
0242   }
0243 }
0244
0245 template <integral _To, class _From>
0246   requires(!integral<_From>)
0247 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_representable_as(_From __value) {
0248   if constexpr (is_signed_v<_To>) {
0249     if (static_cast<_To>(__value) < 0)
0250       return false;
0251   }
0252   return true;
0253 }
0254
0255 template <integral _To, class... _From>
0256 _LIBCPP_HIDE_FROM_ABI constexpr bool __are_representable_as(_From... __values) {
0257   return (__mdspan_detail::__is_representable_as<_To>(__values) && ... && true);
0258 }
0259
0260 template <integral _To, class _From, size_t _Size>
0261 _LIBCPP_HIDE_FROM_ABI constexpr bool __are_representable_as(span<_From, _Size> __values) {
0262   for (size_t __i = 0; __i < _Size; __i++)
0263     if (!__mdspan_detail::__is_representable_as<_To>(__values[__i]))
0264       return false;
0265   return true;
0266 }
0267
0268 } // namespace __mdspan_detail
0269
0270 // ------------------------------------------------------------------
0271 // ------------ extents ---------------------------------------------
0272 // ------------------------------------------------------------------
0273
0274 // Class to describe the extents of a multi dimensional array.
0275 // Used by mdspan, mdarray and layout mappings.
0276 // See ISO C++ standard [mdspan.extents]
0277
0278 template <class _IndexType, size_t... _Extents>
0279 class extents {
0280 public:
0281   // typedefs for integral types used
0282   using index_type = _IndexType;
0283   using size_type  = make_unsigned_t<index_type>;
0284   using rank_type  = size_t;
0285
0286   static_assert(__libcpp_integer<index_type>, "extents::index_type must be a signed or unsigned integer type");
0287   static_assert(((__mdspan_detail::__is_representable_as<index_type>(_Extents) || (_Extents == dynamic_extent)) && ...),
0288                 "extents ctor: arguments must be representable as index_type and nonnegative");
0289
0290 private:
0291   static constexpr rank_type __rank_         = sizeof...(_Extents);
0292   static constexpr rank_type __rank_dynamic_ = ((_Extents == dynamic_extent) + ... + 0);
0293
0294   // internal storage type using __maybe_static_array
0295   using _Values _LIBCPP_NODEBUG =
0296       __mdspan_detail::__maybe_static_array<_IndexType, size_t, dynamic_extent, _Extents...>;
0297   [[no_unique_address]] _Values __vals_;
0298
0299 public:
0300   // [mdspan.extents.obs], observers of multidimensional index space
0301   _LIBCPP_HIDE_FROM_ABI static constexpr rank_type rank() noexcept { return __rank_; }
0302   _LIBCPP_HIDE_FROM_ABI static constexpr rank_type rank_dynamic() noexcept { return __rank_dynamic_; }
0303
0304   _LIBCPP_HIDE_FROM_ABI constexpr index_type extent(rank_type __r) const noexcept { return __vals_.__value(__r); }
0305   _LIBCPP_HIDE_FROM_ABI static constexpr size_t static_extent(rank_type __r) noexcept {
0306     return _Values::__static_value(__r);
0307   }
0308
0309   // [mdspan.extents.cons], constructors
0310   _LIBCPP_HIDE_FROM_ABI constexpr extents() noexcept = default;
0311
0312   // Construction from just dynamic or all values.
0313   // Precondition check is deferred to __maybe_static_array constructor
0314   template <class... _OtherIndexTypes>
0315     requires((is_convertible_v<_OtherIndexTypes, index_type> && ...) &&
0316              (is_nothrow_constructible_v<index_type, _OtherIndexTypes> && ...) &&
0317              (sizeof...(_OtherIndexTypes) == __rank_ || sizeof...(_OtherIndexTypes) == __rank_dynamic_))
0318   _LIBCPP_HIDE_FROM_ABI constexpr explicit extents(_OtherIndexTypes... __dynvals) noexcept
0319       : __vals_(static_cast<index_type>(__dynvals)...) {
0320     // Not catching this could lead to out of bounds errors later
0321     // e.g. mdspan m(ptr, dextents<char, 1>(200u)); leads to an extent of -56 on m
0322     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__mdspan_detail::__are_representable_as<index_type>(__dynvals...),
0323                                         "extents ctor: arguments must be representable as index_type and nonnegative");
0324   }
0325
0326   template <class _OtherIndexType, size_t _Size>
0327     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
0328              is_nothrow_constructible_v<index_type, const _OtherIndexType&> &&
0329              (_Size == __rank_ || _Size == __rank_dynamic_))
0330   explicit(_Size != __rank_dynamic_)
0331       _LIBCPP_HIDE_FROM_ABI constexpr extents(const array<_OtherIndexType, _Size>& __exts) noexcept
0332       : __vals_(span(__exts)) {
0333     // Not catching this could lead to out of bounds errors later
0334     // e.g. mdspan m(ptr, dextents<char, 1>(array<unsigned,1>(200))); leads to an extent of -56 on m
0335     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__mdspan_detail::__are_representable_as<index_type>(span(__exts)),
0336                                         "extents ctor: arguments must be representable as index_type and nonnegative");
0337   }
0338
0339   template <class _OtherIndexType, size_t _Size>
0340     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
0341              is_nothrow_constructible_v<index_type, const _OtherIndexType&> &&
0342              (_Size == __rank_ || _Size == __rank_dynamic_))
0343   explicit(_Size != __rank_dynamic_)
0344       _LIBCPP_HIDE_FROM_ABI constexpr extents(const span<_OtherIndexType, _Size>& __exts) noexcept
0345       : __vals_(__exts) {
0346     // Not catching this could lead to out of bounds errors later
0347     // e.g. array a{200u}; mdspan<int, dextents<char,1>> m(ptr, extents(span<unsigned,1>(a))); leads to an extent of -56
0348     // on m
0349     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__mdspan_detail::__are_representable_as<index_type>(__exts),
0350                                         "extents ctor: arguments must be representable as index_type and nonnegative");
0351   }
0352
0353 private:
0354   // Function to construct extents storage from other extents.
0355   template <size_t _DynCount, size_t _Idx, class _OtherExtents, class... _DynamicValues>
0356     requires(_Idx < __rank_)
0357   _LIBCPP_HIDE_FROM_ABI constexpr _Values __construct_vals_from_extents(
0358       integral_constant<size_t, _DynCount>,
0359       integral_constant<size_t, _Idx>,
0360       const _OtherExtents& __exts,
0361       _DynamicValues... __dynamic_values) noexcept {
0362     if constexpr (static_extent(_Idx) == dynamic_extent)
0363       return __construct_vals_from_extents(
0364           integral_constant<size_t, _DynCount + 1>(),
0365           integral_constant<size_t, _Idx + 1>(),
0366           __exts,
0367           __dynamic_values...,
0368           __exts.extent(_Idx));
0369     else
0370       return __construct_vals_from_extents(
0371           integral_constant<size_t, _DynCount>(), integral_constant<size_t, _Idx + 1>(), __exts, __dynamic_values...);
0372   }
0373
0374   template <size_t _DynCount, size_t _Idx, class _OtherExtents, class... _DynamicValues>
0375     requires((_Idx == __rank_) && (_DynCount == __rank_dynamic_))
0376   _LIBCPP_HIDE_FROM_ABI constexpr _Values __construct_vals_from_extents(
0377       integral_constant<size_t, _DynCount>,
0378       integral_constant<size_t, _Idx>,
0379       const _OtherExtents&,
0380       _DynamicValues... __dynamic_values) noexcept {
0381     return _Values{static_cast<index_type>(__dynamic_values)...};
0382   }
0383
0384 public:
0385   // Converting constructor from other extents specializations
0386   template <class _OtherIndexType, size_t... _OtherExtents>
0387     requires((sizeof...(_OtherExtents) == sizeof...(_Extents)) &&
0388              ((_OtherExtents == dynamic_extent || _Extents == dynamic_extent || _OtherExtents == _Extents) && ...))
0389   explicit((((_Extents != dynamic_extent) && (_OtherExtents == dynamic_extent)) || ...) ||
0390            (static_cast<make_unsigned_t<index_type>>(numeric_limits<index_type>::max()) <
0391             static_cast<make_unsigned_t<_OtherIndexType>>(numeric_limits<_OtherIndexType>::max())))
0392       _LIBCPP_HIDE_FROM_ABI constexpr extents(const extents<_OtherIndexType, _OtherExtents...>& __other) noexcept
0393       : __vals_(
0394             __construct_vals_from_extents(integral_constant<size_t, 0>(), integral_constant<size_t, 0>(), __other)) {
0395     if constexpr (rank() > 0) {
0396       for (size_t __r = 0; __r < rank(); __r++) {
0397         if constexpr (static_cast<make_unsigned_t<index_type>>(numeric_limits<index_type>::max()) <
0398                       static_cast<make_unsigned_t<_OtherIndexType>>(numeric_limits<_OtherIndexType>::max())) {
0399           // Not catching this could lead to out of bounds errors later
0400           // e.g. dextents<char,1>> e(dextents<unsigned,1>(200)) leads to an extent of -56 on e
0401           _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0402               __mdspan_detail::__is_representable_as<index_type>(__other.extent(__r)),
0403               "extents ctor: arguments must be representable as index_type and nonnegative");
0404         }
0405         // Not catching this could lead to out of bounds errors later
0406         // e.g. mdspan<int, extents<int, 10>> m = mdspan<int, dextents<int, 1>>(new int[5], 5);
0407         // Right-hand-side construction was ok, but m now thinks its range is 10 not 5
0408         _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0409             (_Values::__static_value(__r) == dynamic_extent) ||
0410                 (static_cast<index_type>(__other.extent(__r)) == static_cast<index_type>(_Values::__static_value(__r))),
0411             "extents construction: mismatch of provided arguments with static extents.");
0412       }
0413     }
0414   }
0415
0416   // Comparison operator
0417   template <class _OtherIndexType, size_t... _OtherExtents>
0418   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
0419   operator==(const extents& __lhs, const extents<_OtherIndexType, _OtherExtents...>& __rhs) noexcept {
0420     if constexpr (rank() != sizeof...(_OtherExtents)) {
0421       return false;
0422     } else {
0423       for (rank_type __r = 0; __r < __rank_; __r++) {
0424         // avoid warning when comparing signed and unsigner integers and pick the wider of two types
0425         using _CommonType = common_type_t<index_type, _OtherIndexType>;
0426         if (static_cast<_CommonType>(__lhs.extent(__r)) != static_cast<_CommonType>(__rhs.extent(__r))) {
0427           return false;
0428         }
0429       }
0430     }
0431     return true;
0432   }
0433 };
0434
0435 // Recursive helper classes to implement dextents alias for extents
0436 namespace __mdspan_detail {
0437
0438 template <class _IndexType, size_t _Rank, class _Extents = extents<_IndexType>>
0439 struct __make_dextents;
0440
0441 template <class _IndexType, size_t _Rank, size_t... _ExtentsPack>
0442 struct __make_dextents< _IndexType, _Rank, extents<_IndexType, _ExtentsPack...>> {
0443   using type =
0444       typename __make_dextents< _IndexType, _Rank - 1, extents<_IndexType, dynamic_extent, _ExtentsPack...>>::type;
0445 };
0446
0447 template <class _IndexType, size_t... _ExtentsPack>
0448 struct __make_dextents< _IndexType, 0, extents<_IndexType, _ExtentsPack...>> {
0449   using type = extents<_IndexType, _ExtentsPack...>;
0450 };
0451
0452 } // namespace __mdspan_detail
0453
0454 // [mdspan.extents.dextents], alias template
0455 template <class _IndexType, size_t _Rank>
0456 using dextents = typename __mdspan_detail::__make_dextents<_IndexType, _Rank>::type;
0457
0458 #  if _LIBCPP_STD_VER >= 26
0459 // [mdspan.extents.dims], alias template `dims`
0460 template <size_t _Rank, class _IndexType = size_t>
0461 using dims = dextents<_IndexType, _Rank>;
0462 #  endif
0463
0464 // Deduction guide for extents
0465 #  if _LIBCPP_STD_VER >= 26
0466 template <class... _IndexTypes>
0467   requires(is_convertible_v<_IndexTypes, size_t> && ...)
0468 explicit extents(_IndexTypes...) -> extents<size_t, __maybe_static_ext<_IndexTypes>...>;
0469 #  else
0470 template <class... _IndexTypes>
0471   requires(is_convertible_v<_IndexTypes, size_t> && ...)
0472 explicit extents(_IndexTypes...) -> extents<size_t, size_t(((void)sizeof(_IndexTypes), dynamic_extent))...>;
0473 #  endif
0474
0475 namespace __mdspan_detail {
0476
0477 // Helper type traits for identifying a class as extents.
0478 template <class _Tp>
0479 struct __is_extents : false_type {};
0480
0481 template <class _IndexType, size_t... _ExtentsPack>
0482 struct __is_extents<extents<_IndexType, _ExtentsPack...>> : true_type {};
0483
0484 template <class _Tp>
0485 inline constexpr bool __is_extents_v = __is_extents<_Tp>::value;
0486
0487 // Function to check whether a set of indices are a multidimensional
0488 // index into extents. This is a word of power in the C++ standard
0489 // requiring that the indices are larger than 0 and smaller than
0490 // the respective extents.
0491
0492 template <integral _IndexType, class _From>
0493   requires(integral<_From>)
0494 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_index_in_extent(_IndexType __extent, _From __value) {
0495   if constexpr (is_signed_v<_From>) {
0496     if (__value < 0)
0497       return false;
0498   }
0499   using _Tp = common_type_t<_IndexType, _From>;
0500   return static_cast<_Tp>(__value) < static_cast<_Tp>(__extent);
0501 }
0502
0503 template <integral _IndexType, class _From>
0504   requires(!integral<_From>)
0505 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_index_in_extent(_IndexType __extent, _From __value) {
0506   if constexpr (is_signed_v<_IndexType>) {
0507     if (static_cast<_IndexType>(__value) < 0)
0508       return false;
0509   }
0510   return static_cast<_IndexType>(__value) < __extent;
0511 }
0512
0513 template <size_t... _Idxs, class _Extents, class... _From>
0514 _LIBCPP_HIDE_FROM_ABI constexpr bool
0515 __is_multidimensional_index_in_impl(index_sequence<_Idxs...>, const _Extents& __ext, _From... __values) {
0516   return (__mdspan_detail::__is_index_in_extent(__ext.extent(_Idxs), __values) && ...);
0517 }
0518
0519 template <class _Extents, class... _From>
0520 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_multidimensional_index_in(const _Extents& __ext, _From... __values) {
0521   return __mdspan_detail::__is_multidimensional_index_in_impl(
0522       make_index_sequence<_Extents::rank()>(), __ext, __values...);
0523 }
0524
0525 } // namespace __mdspan_detail
0526
0527 #endif // _LIBCPP_STD_VER >= 23
0528
0529 _LIBCPP_END_NAMESPACE_STD
0530
0531 _LIBCPP_POP_MACROS
0532
0533 #endif // _LIBCPP___MDSPAN_EXTENTS_H