__cxx03/__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___CXX03___MDSPAN_LAYOUT_LEFT_H
0018 #define _LIBCPP___CXX03___MDSPAN_LAYOUT_LEFT_H
0019
0020 #include <__cxx03/__assert>
0021 #include <__cxx03/__config>
0022 #include <__cxx03/__fwd/mdspan.h>
0023 #include <__cxx03/__mdspan/extents.h>
0024 #include <__cxx03/__type_traits/is_constructible.h>
0025 #include <__cxx03/__type_traits/is_convertible.h>
0026 #include <__cxx03/__type_traits/is_nothrow_constructible.h>
0027 #include <__cxx03/__utility/integer_sequence.h>
0028 #include <__cxx03/array>
0029 #include <__cxx03/cinttypes>
0030 #include <__cxx03/cstddef>
0031 #include <__cxx03/limits>
0032
0033 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0034 #  pragma GCC system_header
0035 #endif
0036
0037 _LIBCPP_PUSH_MACROS
0038 #include <__cxx03/__undef_macros>
0039
0040 _LIBCPP_BEGIN_NAMESPACE_STD
0041
0042 #if _LIBCPP_STD_VER >= 23
0043
0044 template <class _Extents>
0045 class layout_left::mapping {
0046 public:
0047   static_assert(__mdspan_detail::__is_extents<_Extents>::value,
0048                 "layout_left::mapping template argument must be a specialization of extents.");
0049
0050   using extents_type = _Extents;
0051   using index_type   = typename extents_type::index_type;
0052   using size_type    = typename extents_type::size_type;
0053   using rank_type    = typename extents_type::rank_type;
0054   using layout_type  = layout_left;
0055
0056 private:
0057   _LIBCPP_HIDE_FROM_ABI static constexpr bool __required_span_size_is_representable(const extents_type& __ext) {
0058     if constexpr (extents_type::rank() == 0)
0059       return true;
0060
0061     index_type __prod = __ext.extent(0);
0062     for (rank_type __r = 1; __r < extents_type::rank(); __r++) {
0063       bool __overflowed = __builtin_mul_overflow(__prod, __ext.extent(__r), &__prod);
0064       if (__overflowed)
0065         return false;
0066     }
0067     return true;
0068   }
0069
0070   static_assert(extents_type::rank_dynamic() > 0 || __required_span_size_is_representable(extents_type()),
0071                 "layout_left::mapping product of static extents must be representable as index_type.");
0072
0073 public:
0074   // [mdspan.layout.left.cons], constructors
0075   _LIBCPP_HIDE_FROM_ABI constexpr mapping() noexcept               = default;
0076   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const mapping&) noexcept = default;
0077   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext) noexcept : __extents_(__ext) {
0078     // not catching this could lead to out-of-bounds access later when used inside mdspan
0079     // mapping<dextents<char, 2>> map(dextents<char, 2>(40,40)); map(10, 3) == -126
0080     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0081         __required_span_size_is_representable(__ext),
0082         "layout_left::mapping extents ctor: product of extents must be representable as index_type.");
0083   }
0084
0085   template <class _OtherExtents>
0086     requires(is_constructible_v<extents_type, _OtherExtents>)
0087   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherExtents, extents_type>)
0088       mapping(const mapping<_OtherExtents>& __other) noexcept
0089       : __extents_(__other.extents()) {
0090     // not catching this could lead to out-of-bounds access later when used inside mdspan
0091     // mapping<dextents<char, 2>> map(mapping<dextents<int, 2>>(dextents<int, 2>(40,40))); map(10, 3) == -126
0092     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0093         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0094         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
0095   }
0096
0097   template <class _OtherExtents>
0098     requires(is_constructible_v<extents_type, _OtherExtents> && _OtherExtents::rank() <= 1)
0099   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherExtents, extents_type>)
0100       mapping(const layout_right::mapping<_OtherExtents>& __other) noexcept
0101       : __extents_(__other.extents()) {
0102     // not catching this could lead to out-of-bounds access later when used inside mdspan
0103     // Note: since this is constraint to rank 1, extents itself would catch the invalid conversion first
0104     //       and thus this assertion should never be triggered, but keeping it here for consistency
0105     // layout_left::mapping<dextents<char, 1>> map(
0106     //           layout_right::mapping<dextents<unsigned, 1>>(dextents<unsigned, 1>(200))); map.extents().extent(0) ==
0107     //           -56
0108     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0109         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0110         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
0111   }
0112
0113   template <class _OtherExtents>
0114     requires(is_constructible_v<extents_type, _OtherExtents>)
0115   _LIBCPP_HIDE_FROM_ABI constexpr explicit(extents_type::rank() > 0)
0116       mapping(const layout_stride::mapping<_OtherExtents>& __other) noexcept
0117       : __extents_(__other.extents()) {
0118     if constexpr (extents_type::rank() > 0) {
0119       _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0120           ([&]() {
0121             using _CommonType = common_type_t<typename extents_type::index_type, typename _OtherExtents::index_type>;
0122             for (rank_type __r = 0; __r < extents_type::rank(); __r++)
0123               if (static_cast<_CommonType>(stride(__r)) != static_cast<_CommonType>(__other.stride(__r)))
0124                 return false;
0125             return true;
0126           }()),
0127           "layout_left::mapping from layout_stride ctor: strides are not compatible with layout_left.");
0128       _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0129           __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
0130           "layout_left::mapping from layout_stride ctor: other.required_span_size() must be representable as "
0131           "index_type.");
0132     }
0133   }
0134
0135   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
0136
0137   // [mdspan.layout.left.obs], observers
0138   _LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __extents_; }
0139
0140   _LIBCPP_HIDE_FROM_ABI constexpr index_type required_span_size() const noexcept {
0141     index_type __size = 1;
0142     for (size_t __r = 0; __r < extents_type::rank(); __r++)
0143       __size *= __extents_.extent(__r);
0144     return __size;
0145   }
0146
0147   template <class... _Indices>
0148     requires((sizeof...(_Indices) == extents_type::rank()) && (is_convertible_v<_Indices, index_type> && ...) &&
0149              (is_nothrow_constructible_v<index_type, _Indices> && ...))
0150   _LIBCPP_HIDE_FROM_ABI constexpr index_type operator()(_Indices... __idx) const noexcept {
0151     // Mappings are generally meant to be used for accessing allocations and are meant to guarantee to never
0152     // return a value exceeding required_span_size(), which is used to know how large an allocation one needs
0153     // Thus, this is a canonical point in multi-dimensional data structures to make invalid element access checks
0154     // However, mdspan does check this on its own, so for now we avoid double checking in hardened mode
0155     _LIBCPP_ASSERT_UNCATEGORIZED(__mdspan_detail::__is_multidimensional_index_in(__extents_, __idx...),
0156                                  "layout_left::mapping: out of bounds indexing");
0157     array<index_type, extents_type::rank()> __idx_a{static_cast<index_type>(__idx)...};
0158     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
0159       index_type __res = 0;
0160       ((__res = __idx_a[extents_type::rank() - 1 - _Pos] + __extents_.extent(extents_type::rank() - 1 - _Pos) * __res),
0161        ...);
0162       return __res;
0163     }(make_index_sequence<sizeof...(_Indices)>());
0164   }
0165
0166   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return true; }
0167   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept { return true; }
0168   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept { return true; }
0169
0170   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_unique() noexcept { return true; }
0171   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_exhaustive() noexcept { return true; }
0172   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_strided() noexcept { return true; }
0173
0174   _LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const noexcept
0175     requires(extents_type::rank() > 0)
0176   {
0177     // While it would be caught by extents itself too, using a too large __r
0178     // is functionally an out of bounds access on the stored information needed to compute strides
0179     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
0180         __r < extents_type::rank(), "layout_left::mapping::stride(): invalid rank index");
0181     index_type __s = 1;
0182     for (rank_type __i = 0; __i < __r; __i++)
0183       __s *= __extents_.extent(__i);
0184     return __s;
0185   }
0186
0187   template <class _OtherExtents>
0188     requires(_OtherExtents::rank() == extents_type::rank())
0189   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
0190   operator==(const mapping& __lhs, const mapping<_OtherExtents>& __rhs) noexcept {
0191     return __lhs.extents() == __rhs.extents();
0192   }
0193
0194 private:
0195   _LIBCPP_NO_UNIQUE_ADDRESS extents_type __extents_{};
0196 };
0197
0198 #endif // _LIBCPP_STD_VER >= 23
0199
0200 _LIBCPP_END_NAMESPACE_STD
0201
0202 _LIBCPP_POP_MACROS
0203
0204 #endif // _LIBCPP___CXX03___MDSPAN_LAYOUT_LEFT_H