v1/__mdspan/layout_stride.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_LAYOUT_STRIDE_H
0018 #define _LIBCPP___MDSPAN_LAYOUT_STRIDE_H
0019
0020 #include <__assert>
0021 #include <__concepts/same_as.h>
0022 #include <__config>
0023 #include <__fwd/mdspan.h>
0024 #include <__mdspan/extents.h>
0025 #include <__type_traits/common_type.h>
0026 #include <__type_traits/is_constructible.h>
0027 #include <__type_traits/is_convertible.h>
0028 #include <__type_traits/is_integral.h>
0029 #include <__type_traits/is_nothrow_constructible.h>
0030 #include <__type_traits/is_same.h>
0031 #include <__utility/as_const.h>
0032 #include <__utility/integer_sequence.h>
0033 #include <__utility/swap.h>
0034 #include <array>
0035 #include <limits>
0036 #include <span>
0037
0038 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0039 #  pragma GCC system_header
0040 #endif
0041
0042 _LIBCPP_PUSH_MACROS
0043 #include <__undef_macros>
0044
0045 _LIBCPP_BEGIN_NAMESPACE_STD
0046
0047 #if _LIBCPP_STD_VER >= 23
0048
0049 namespace __mdspan_detail {
0050 template <class _Layout, class _Mapping>
0051 constexpr bool __is_mapping_of =
0052     is_same_v<typename _Layout::template mapping<typename _Mapping::extents_type>, _Mapping>;
0053
0054 template <class _Mapping>
0055 concept __layout_mapping_alike = requires {
0056   requires __is_mapping_of<typename _Mapping::layout_type, _Mapping>;
0057   requires __is_extents_v<typename _Mapping::extents_type>;
0058   { _Mapping::is_always_strided() } -> same_as<bool>;
0059   { _Mapping::is_always_exhaustive() } -> same_as<bool>;
0060   { _Mapping::is_always_unique() } -> same_as<bool>;
0061   bool_constant<_Mapping::is_always_strided()>::value;
0062   bool_constant<_Mapping::is_always_exhaustive()>::value;
0063   bool_constant<_Mapping::is_always_unique()>::value;
0064 };
0065 } // namespace __mdspan_detail
0066
0067 template <class _Extents>
0068 class layout_stride::mapping {
0069 public:
0070   static_assert(__mdspan_detail::__is_extents<_Extents>::value,
0071                 "layout_stride::mapping template argument must be a specialization of extents.");
0072
0073   using extents_type = _Extents;
0074   using index_type   = typename extents_type::index_type;
0075   using size_type    = typename extents_type::size_type;
0076   using rank_type    = typename extents_type::rank_type;
0077   using layout_type  = layout_stride;
0078
0079 private:
0080   static constexpr rank_type __rank_ = extents_type::rank();
0081
0082   // Used for default construction check and mandates
0083   _LIBCPP_HIDE_FROM_ABI static constexpr bool __required_span_size_is_representable(const extents_type& __ext) {
0084     if constexpr (__rank_ == 0)
0085       return true;
0086
0087     index_type __prod = __ext.extent(0);
0088     for (rank_type __r = 1; __r < __rank_; __r++) {
0089       bool __overflowed = __builtin_mul_overflow(__prod, __ext.extent(__r), &__prod);
0090       if (__overflowed)
0091         return false;
0092     }
0093     return true;
0094   }
0095
0096   template <class _OtherIndexType>
0097   _LIBCPP_HIDE_FROM_ABI static constexpr bool
0098   __required_span_size_is_representable(const extents_type& __ext, span<_OtherIndexType, __rank_> __strides) {
0099     if constexpr (__rank_ == 0)
0100       return true;
0101
0102     index_type __size = 1;
0103     for (rank_type __r = 0; __r < __rank_; __r++) {
0104       // We can only check correct conversion of _OtherIndexType if it is an integral
0105       if constexpr (is_integral_v<_OtherIndexType>) {
0106         using _CommonType = common_type_t<index_type, _OtherIndexType>;
0107         if (static_cast<_CommonType>(__strides[__r]) > static_cast<_CommonType>(numeric_limits<index_type>::max()))
0108           return false;
0109       }
0110       if (__ext.extent(__r) == static_cast<index_type>(0))
0111         return true;
0112       index_type __prod     = (__ext.extent(__r) - 1);
0113       bool __overflowed_mul = __builtin_mul_overflow(__prod, static_cast<index_type>(__strides[__r]), &__prod);
0114       if (__overflowed_mul)
0115         return false;
0116       bool __overflowed_add = __builtin_add_overflow(__size, __prod, &__size);
0117       if (__overflowed_add)
0118         return false;
0119     }
0120     return true;
0121   }
0122
0123   // compute offset of a strided layout mapping
0124   template <class _StridedMapping>
0125   _LIBCPP_HIDE_FROM_ABI static constexpr index_type __offset(const _StridedMapping& __mapping) {
0126     if constexpr (_StridedMapping::extents_type::rank() == 0) {
0127       return static_cast<index_type>(__mapping());
0128     } else if (__mapping.required_span_size() == static_cast<typename _StridedMapping::index_type>(0)) {
0129       return static_cast<index_type>(0);
0130     } else {
0131       return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0132         return static_cast<index_type>(__mapping((_Pos ? 0 : 0)...));
0133       }(make_index_sequence<__rank_>());
0134     }
0135   }
0136
0137   // compute the permutation for sorting the stride array
0138   // we never actually sort the stride array
0139   _LIBCPP_HIDE_FROM_ABI constexpr void __bubble_sort_by_strides(array<rank_type, __rank_>& __permute) const {
0140     for (rank_type __i = __rank_ - 1; __i > 0; __i--) {
0141       for (rank_type __r = 0; __r < __i; __r++) {
0142         if (__strides_[__permute[__r]] > __strides_[__permute[__r + 1]]) {
0143           swap(__permute[__r], __permute[__r + 1]);
0144         } else {
0145           // if two strides are the same then one of the associated extents must be 1 or 0
0146           // both could be, but you can't have one larger than 1 come first
0147           if ((__strides_[__permute[__r]] == __strides_[__permute[__r + 1]]) &&
0148               (__extents_.extent(__permute[__r]) > static_cast<index_type>(1)))
0149             swap(__permute[__r], __permute[__r + 1]);
0150         }
0151       }
0152     }
0153   }
0154
0155   static_assert(extents_type::rank_dynamic() > 0 || __required_span_size_is_representable(extents_type()),
0156                 "layout_stride::mapping product of static extents must be representable as index_type.");
0157
0158 public:
0159   // [mdspan.layout.stride.cons], constructors
0160   _LIBCPP_HIDE_FROM_ABI constexpr mapping() noexcept : __extents_(extents_type()) {
0161     // Note the nominal precondition is covered by above static assert since
0162     // if rank_dynamic is != 0 required_span_size is zero for default construction
0163     if constexpr (__rank_ > 0) {
0164       index_type __stride = 1;
0165       for (rank_type __r = __rank_ - 1; __r > static_cast<rank_type>(0); __r--) {
0166         __strides_[__r] = __stride;
0167         __stride *= __extents_.extent(__r);
0168       }
0169       __strides_[0] = __stride;
0170     }
0171   }
0172
0173   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const mapping&) noexcept = default;
0174
0175   template <class _OtherIndexType>
0176     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
0177              is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
0178   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext, span<_OtherIndexType, __rank_> __strides) noexcept
0179       : __extents_(__ext), __strides_([&]<size_t... _Pos>(index_sequence<_Pos...>) {
0180           return __mdspan_detail::__possibly_empty_array<index_type, __rank_>{
0181               static_cast<index_type>(std::as_const(__strides[_Pos]))...};
0182         }(make_index_sequence<__rank_>())) {
0183     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0184         ([&]<size_t... _Pos>(index_sequence<_Pos...>) {
0185           // For integrals we can do a pre-conversion check, for other types not
0186           if constexpr (is_integral_v<_OtherIndexType>) {
0187             return ((__strides[_Pos] > static_cast<_OtherIndexType>(0)) && ... && true);
0188           } else {
0189             return ((static_cast<index_type>(__strides[_Pos]) > static_cast<index_type>(0)) && ... && true);
0190           }
0191         }(make_index_sequence<__rank_>())),
0192         "layout_stride::mapping ctor: all strides must be greater than 0");
0193     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0194         __required_span_size_is_representable(__ext, __strides),
0195         "layout_stride::mapping ctor: required span size is not representable as index_type.");
0196     if constexpr (__rank_ > 1) {
0197       _LIBCPP_ASSERT_UNCATEGORIZED(
0198           ([&]<size_t... _Pos>(index_sequence<_Pos...>) {
0199             // basically sort the dimensions based on strides and extents, sorting is represented in permute array
0200             array<rank_type, __rank_> __permute{_Pos...};
0201             __bubble_sort_by_strides(__permute);
0202
0203             // check that this permutations represents a growing set
0204             for (rank_type __i = 1; __i < __rank_; __i++)
0205               if (static_cast<index_type>(__strides[__permute[__i]]) <
0206                   static_cast<index_type>(__strides[__permute[__i - 1]]) * __extents_.extent(__permute[__i - 1]))
0207                 return false;
0208             return true;
0209           }(make_index_sequence<__rank_>())),
0210           "layout_stride::mapping ctor: the provided extents and strides lead to a non-unique mapping");
0211     }
0212   }
0213
0214   template <class _OtherIndexType>
0215     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
0216              is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
0217   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext,
0218                                           const array<_OtherIndexType, __rank_>& __strides) noexcept
0219       : mapping(__ext, span(__strides)) {}
0220
0221   template <class _StridedLayoutMapping>
0222     requires(__mdspan_detail::__layout_mapping_alike<_StridedLayoutMapping> &&
0223              is_constructible_v<extents_type, typename _StridedLayoutMapping::extents_type> &&
0224              _StridedLayoutMapping::is_always_unique() && _StridedLayoutMapping::is_always_strided())
0225   _LIBCPP_HIDE_FROM_ABI constexpr explicit(
0226       !(is_convertible_v<typename _StridedLayoutMapping::extents_type, extents_type> &&
0227         (__mdspan_detail::__is_mapping_of<layout_left, _StridedLayoutMapping> ||
0228          __mdspan_detail::__is_mapping_of<layout_right, _StridedLayoutMapping> ||
0229          __mdspan_detail::__is_mapping_of<layout_stride, _StridedLayoutMapping>)))
0230       mapping(const _StridedLayoutMapping& __other) noexcept
0231       : __extents_(__other.extents()), __strides_([&]<size_t... _Pos>(index_sequence<_Pos...>) {
0232           // stride() only compiles for rank > 0
0233           if constexpr (__rank_ > 0) {
0234             return __mdspan_detail::__possibly_empty_array<index_type, __rank_>{
0235                 static_cast<index_type>(__other.stride(_Pos))...};
0236           } else {
0237             return __mdspan_detail::__possibly_empty_array<index_type, 0>{};
0238           }
0239         }(make_index_sequence<__rank_>())) {
0240     // stride() only compiles for rank > 0
0241     if constexpr (__rank_ > 0) {
0242       _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0243           ([&]<size_t... _Pos>(index_sequence<_Pos...>) {
0244             return ((static_cast<index_type>(__other.stride(_Pos)) > static_cast<index_type>(0)) && ... && true);
0245           }(make_index_sequence<__rank_>())),
0246           "layout_stride::mapping converting ctor: all strides must be greater than 0");
0247     }
0248     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0249         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0250         "layout_stride::mapping converting ctor: other.required_span_size() must be representable as index_type.");
0251     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(static_cast<index_type>(0) == __offset(__other),
0252                                         "layout_stride::mapping converting ctor: base offset of mapping must be zero.");
0253   }
0254
0255   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
0256
0257   // [mdspan.layout.stride.obs], observers
0258   _LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __extents_; }
0259
0260   _LIBCPP_HIDE_FROM_ABI constexpr array<index_type, __rank_> strides() const noexcept {
0261     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0262       return array<index_type, __rank_>{__strides_[_Pos]...};
0263     }(make_index_sequence<__rank_>());
0264   }
0265
0266   _LIBCPP_HIDE_FROM_ABI constexpr index_type required_span_size() const noexcept {
0267     if constexpr (__rank_ == 0) {
0268       return static_cast<index_type>(1);
0269     } else {
0270       return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0271         if ((__extents_.extent(_Pos) * ... * 1) == 0)
0272           return static_cast<index_type>(0);
0273         else
0274           return static_cast<index_type>(
0275               static_cast<index_type>(1) +
0276               (((__extents_.extent(_Pos) - static_cast<index_type>(1)) * __strides_[_Pos]) + ... +
0277                static_cast<index_type>(0)));
0278       }(make_index_sequence<__rank_>());
0279     }
0280   }
0281
0282   template <class... _Indices>
0283     requires((sizeof...(_Indices) == __rank_) && (is_convertible_v<_Indices, index_type> && ...) &&
0284              (is_nothrow_constructible_v<index_type, _Indices> && ...))
0285   _LIBCPP_HIDE_FROM_ABI constexpr index_type operator()(_Indices... __idx) const noexcept {
0286     // Mappings are generally meant to be used for accessing allocations and are meant to guarantee to never
0287     // return a value exceeding required_span_size(), which is used to know how large an allocation one needs
0288     // Thus, this is a canonical point in multi-dimensional data structures to make invalid element access checks
0289     // However, mdspan does check this on its own, so for now we avoid double checking in hardened mode
0290     _LIBCPP_ASSERT_UNCATEGORIZED(__mdspan_detail::__is_multidimensional_index_in(__extents_, __idx...),
0291                                  "layout_stride::mapping: out of bounds indexing");
0292     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0293       return ((static_cast<index_type>(__idx) * __strides_[_Pos]) + ... + index_type(0));
0294     }(make_index_sequence<sizeof...(_Indices)>());
0295   }
0296
0297   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return true; }
0298   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept { return false; }
0299   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept { return true; }
0300
0301   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_unique() noexcept { return true; }
0302   // The answer of this function is fairly complex in the case where one or more
0303   // extents are zero.
0304   // Technically it is meaningless to query is_exhaustive() in that case, but unfortunately
0305   // the way the standard defines this function, we can't give a simple true or false then.
0306   _LIBCPP_HIDE_FROM_ABI constexpr bool is_exhaustive() const noexcept {
0307     if constexpr (__rank_ == 0)
0308       return true;
0309     else {
0310       index_type __span_size = required_span_size();
0311       if (__span_size == static_cast<index_type>(0)) {
0312         if constexpr (__rank_ == 1)
0313           return __strides_[0] == 1;
0314         else {
0315           rank_type __r_largest = 0;
0316           for (rank_type __r = 1; __r < __rank_; __r++)
0317             if (__strides_[__r] > __strides_[__r_largest])
0318               __r_largest = __r;
0319           for (rank_type __r = 0; __r < __rank_; __r++)
0320             if (__extents_.extent(__r) == 0 && __r != __r_largest)
0321               return false;
0322           return true;
0323         }
0324       } else {
0325         return required_span_size() == [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0326           return (__extents_.extent(_Pos) * ... * static_cast<index_type>(1));
0327         }(make_index_sequence<__rank_>());
0328       }
0329     }
0330   }
0331   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_strided() noexcept { return true; }
0332
0333   // according to the standard layout_stride does not have a constraint on stride(r) for rank>0
0334   // it still has the precondition though
0335   _LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const noexcept {
0336     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__r < __rank_, "layout_stride::mapping::stride(): invalid rank index");
0337     return __strides_[__r];
0338   }
0339
0340   template <class _OtherMapping>
0341     requires(__mdspan_detail::__layout_mapping_alike<_OtherMapping> &&
0342              (_OtherMapping::extents_type::rank() == __rank_) && _OtherMapping::is_always_strided())
0343   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const mapping& __lhs, const _OtherMapping& __rhs) noexcept {
0344     if (__offset(__rhs))
0345       return false;
0346     if constexpr (__rank_ == 0)
0347       return true;
0348     else {
0349       return __lhs.extents() == __rhs.extents() && [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0350         // avoid warning when comparing signed and unsigner integers and pick the wider of two types
0351         using _CommonType = common_type_t<index_type, typename _OtherMapping::index_type>;
0352         return ((static_cast<_CommonType>(__lhs.stride(_Pos)) == static_cast<_CommonType>(__rhs.stride(_Pos))) && ... &&
0353                 true);
0354       }(make_index_sequence<__rank_>());
0355     }
0356   }
0357
0358 private:
0359   _LIBCPP_NO_UNIQUE_ADDRESS extents_type __extents_{};
0360   _LIBCPP_NO_UNIQUE_ADDRESS __mdspan_detail::__possibly_empty_array<index_type, __rank_> __strides_{};
0361 };
0362
0363 #endif // _LIBCPP_STD_VER >= 23
0364
0365 _LIBCPP_END_NAMESPACE_STD
0366
0367 _LIBCPP_POP_MACROS
0368
0369 #endif // _LIBCPP___MDSPAN_LAYOUT_STRIDE_H