v1/__mdspan/layout_left.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_LEFT_H
0018 #define _LIBCPP___MDSPAN_LAYOUT_LEFT_H
0019
0020 #include <__assert>
0021 #include <__config>
0022 #include <__fwd/mdspan.h>
0023 #include <__mdspan/extents.h>
0024 #include <__type_traits/common_type.h>
0025 #include <__type_traits/is_constructible.h>
0026 #include <__type_traits/is_convertible.h>
0027 #include <__type_traits/is_nothrow_constructible.h>
0028 #include <__utility/integer_sequence.h>
0029 #include <array>
0030
0031 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0032 #  pragma GCC system_header
0033 #endif
0034
0035 _LIBCPP_PUSH_MACROS
0036 #include <__undef_macros>
0037
0038 _LIBCPP_BEGIN_NAMESPACE_STD
0039
0040 #if _LIBCPP_STD_VER >= 23
0041
0042 template <class _Extents>
0043 class layout_left::mapping {
0044 public:
0045   static_assert(__mdspan_detail::__is_extents<_Extents>::value,
0046                 "layout_left::mapping template argument must be a specialization of extents.");
0047
0048   using extents_type = _Extents;
0049   using index_type   = typename extents_type::index_type;
0050   using size_type    = typename extents_type::size_type;
0051   using rank_type    = typename extents_type::rank_type;
0052   using layout_type  = layout_left;
0053
0054 private:
0055   _LIBCPP_HIDE_FROM_ABI static constexpr bool __required_span_size_is_representable(const extents_type& __ext) {
0056     if constexpr (extents_type::rank() == 0)
0057       return true;
0058
0059     index_type __prod = __ext.extent(0);
0060     for (rank_type __r = 1; __r < extents_type::rank(); __r++) {
0061       bool __overflowed = __builtin_mul_overflow(__prod, __ext.extent(__r), &__prod);
0062       if (__overflowed)
0063         return false;
0064     }
0065     return true;
0066   }
0067
0068   static_assert(extents_type::rank_dynamic() > 0 || __required_span_size_is_representable(extents_type()),
0069                 "layout_left::mapping product of static extents must be representable as index_type.");
0070
0071 public:
0072   // [mdspan.layout.left.cons], constructors
0073   _LIBCPP_HIDE_FROM_ABI constexpr mapping() noexcept               = default;
0074   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const mapping&) noexcept = default;
0075   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext) noexcept : __extents_(__ext) {
0076     // not catching this could lead to out-of-bounds access later when used inside mdspan
0077     // mapping<dextents<char, 2>> map(dextents<char, 2>(40,40)); map(10, 3) == -126
0078     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0079         __required_span_size_is_representable(__ext),
0080         "layout_left::mapping extents ctor: product of extents must be representable as index_type.");
0081   }
0082
0083   template <class _OtherExtents>
0084     requires(is_constructible_v<extents_type, _OtherExtents>)
0085   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherExtents, extents_type>)
0086       mapping(const mapping<_OtherExtents>& __other) noexcept
0087       : __extents_(__other.extents()) {
0088     // not catching this could lead to out-of-bounds access later when used inside mdspan
0089     // mapping<dextents<char, 2>> map(mapping<dextents<int, 2>>(dextents<int, 2>(40,40))); map(10, 3) == -126
0090     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0091         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0092         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
0093   }
0094
0095   template <class _OtherExtents>
0096     requires(is_constructible_v<extents_type, _OtherExtents> && _OtherExtents::rank() <= 1)
0097   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherExtents, extents_type>)
0098       mapping(const layout_right::mapping<_OtherExtents>& __other) noexcept
0099       : __extents_(__other.extents()) {
0100     // not catching this could lead to out-of-bounds access later when used inside mdspan
0101     // Note: since this is constraint to rank 1, extents itself would catch the invalid conversion first
0102     //       and thus this assertion should never be triggered, but keeping it here for consistency
0103     // layout_left::mapping<dextents<char, 1>> map(
0104     //           layout_right::mapping<dextents<unsigned, 1>>(dextents<unsigned, 1>(200))); map.extents().extent(0) ==
0105     //           -56
0106     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0107         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0108         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
0109   }
0110
0111   template <class _OtherExtents>
0112     requires(is_constructible_v<extents_type, _OtherExtents>)
0113   _LIBCPP_HIDE_FROM_ABI constexpr explicit(extents_type::rank() > 0)
0114       mapping(const layout_stride::mapping<_OtherExtents>& __other) noexcept
0115       : __extents_(__other.extents()) {
0116     if constexpr (extents_type::rank() > 0) {
0117       _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0118           ([&]() {
0119             using _CommonType = common_type_t<typename extents_type::index_type, typename _OtherExtents::index_type>;
0120             for (rank_type __r = 0; __r < extents_type::rank(); __r++)
0121               if (static_cast<_CommonType>(stride(__r)) != static_cast<_CommonType>(__other.stride(__r)))
0122                 return false;
0123             return true;
0124           }()),
0125           "layout_left::mapping from layout_stride ctor: strides are not compatible with layout_left.");
0126       _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0127           __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0128           "layout_left::mapping from layout_stride ctor: other.required_span_size() must be representable as "
0129           "index_type.");
0130     }
0131   }
0132
0133   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
0134
0135   // [mdspan.layout.left.obs], observers
0136   _LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __extents_; }
0137
0138   _LIBCPP_HIDE_FROM_ABI constexpr index_type required_span_size() const noexcept {
0139     index_type __size = 1;
0140     for (size_t __r = 0; __r < extents_type::rank(); __r++)
0141       __size *= __extents_.extent(__r);
0142     return __size;
0143   }
0144
0145   template <class... _Indices>
0146     requires((sizeof...(_Indices) == extents_type::rank()) && (is_convertible_v<_Indices, index_type> && ...) &&
0147              (is_nothrow_constructible_v<index_type, _Indices> && ...))
0148   _LIBCPP_HIDE_FROM_ABI constexpr index_type operator()(_Indices... __idx) const noexcept {
0149     // Mappings are generally meant to be used for accessing allocations and are meant to guarantee to never
0150     // return a value exceeding required_span_size(), which is used to know how large an allocation one needs
0151     // Thus, this is a canonical point in multi-dimensional data structures to make invalid element access checks
0152     // However, mdspan does check this on its own, so for now we avoid double checking in hardened mode
0153     _LIBCPP_ASSERT_UNCATEGORIZED(__mdspan_detail::__is_multidimensional_index_in(__extents_, __idx...),
0154                                  "layout_left::mapping: out of bounds indexing");
0155     array<index_type, extents_type::rank()> __idx_a{static_cast<index_type>(__idx)...};
0156     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0157       index_type __res = 0;
0158       ((__res = __idx_a[extents_type::rank() - 1 - _Pos] + __extents_.extent(extents_type::rank() - 1 - _Pos) * __res),
0159        ...);
0160       return __res;
0161     }(make_index_sequence<sizeof...(_Indices)>());
0162   }
0163
0164   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return true; }
0165   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept { return true; }
0166   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept { return true; }
0167
0168   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_unique() noexcept { return true; }
0169   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_exhaustive() noexcept { return true; }
0170   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_strided() noexcept { return true; }
0171
0172   _LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const noexcept
0173     requires(extents_type::rank() > 0)
0174   {
0175     // While it would be caught by extents itself too, using a too large __r
0176     // is functionally an out of bounds access on the stored information needed to compute strides
0177     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0178         __r < extents_type::rank(), "layout_left::mapping::stride(): invalid rank index");
0179     index_type __s = 1;
0180     for (rank_type __i = 0; __i < __r; __i++)
0181       __s *= __extents_.extent(__i);
0182     return __s;
0183   }
0184
0185   template <class _OtherExtents>
0186     requires(_OtherExtents::rank() == extents_type::rank())
0187   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
0188   operator==(const mapping& __lhs, const mapping<_OtherExtents>& __rhs) noexcept {
0189     return __lhs.extents() == __rhs.extents();
0190   }
0191
0192 private:
0193   _LIBCPP_NO_UNIQUE_ADDRESS extents_type __extents_{};
0194 };
0195
0196 #endif // _LIBCPP_STD_VER >= 23
0197
0198 _LIBCPP_END_NAMESPACE_STD
0199
0200 _LIBCPP_POP_MACROS
0201
0202 #endif // _LIBCPP___MDSPAN_LAYOUT_LEFT_H