libcxx/include/__mdspan/layout_left.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //                        Kokkos v. 4.0
   9 //       Copyright (2022) National Technology & Engineering
  10 //               Solutions of Sandia, LLC (NTESS).
  11 //
  12 // Under the terms of Contract DE-NA0003525 with NTESS,
  13 // the U.S. Government retains certain rights in this software.
  14 //
  15 //===---------------------------------------------------------------------===//
  16
  17 #ifndef _LIBCPP___MDSPAN_LAYOUT_LEFT_H
  18 #define _LIBCPP___MDSPAN_LAYOUT_LEFT_H
  19
  20 #include <__assert>
  21 #include <__config>
  22 #include <__fwd/mdspan.h>
  23 #include <__mdspan/extents.h>
  24 #include <__type_traits/is_constructible.h>
  25 #include <__type_traits/is_convertible.h>
  26 #include <__type_traits/is_nothrow_constructible.h>
  27 #include <__utility/integer_sequence.h>
  28 #include <array>
  29 #include <cinttypes>
  30 #include <cstddef>
  31 #include <limits>
  32
  33 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  34 #  pragma GCC system_header
  35 #endif
  36
  37 _LIBCPP_PUSH_MACROS
  38 #include <__undef_macros>
  39
  40 _LIBCPP_BEGIN_NAMESPACE_STD
  41
  42 #if _LIBCPP_STD_VER >= 23
  43
  44 template <class _Extents>
  45 class layout_left::mapping {
  46 public:
  47   static_assert(__mdspan_detail::__is_extents<_Extents>::value,
  48                 "layout_left::mapping template argument must be a specialization of extents.");
  49
  50   using extents_type = _Extents;
  51   using index_type   = typename extents_type::index_type;
  52   using size_type    = typename extents_type::size_type;
  53   using rank_type    = typename extents_type::rank_type;
  54   using layout_type  = layout_left;
  55
  56 private:
  57   _LIBCPP_HIDE_FROM_ABI static constexpr bool __required_span_size_is_representable(const extents_type& __ext) {
  58     if constexpr (extents_type::rank() == 0)
  59       return true;
  60
  61     index_type __prod = __ext.extent(0);
  62     for (rank_type __r = 1; __r < extents_type::rank(); __r++) {
  63       bool __overflowed = __builtin_mul_overflow(__prod, __ext.extent(__r), &__prod);
  64       if (__overflowed)
  65         return false;
  66     }
  67     return true;
  68   }
  69
  70   static_assert((extents_type::rank_dynamic() > 0) || __required_span_size_is_representable(extents_type()),
  71                 "layout_left::mapping product of static extents must be representable as index_type.");
  72
  73 public:
  74   // [mdspan.layout.left.cons], constructors
  75   _LIBCPP_HIDE_FROM_ABI constexpr mapping() noexcept               = default;
  76   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const mapping&) noexcept = default;
  77   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext) noexcept : __extents_(__ext) {
  78     // not catching this could lead to out-of-bounds access later when used inside mdspan
  79     // mapping<dextents<char, 2>> map(dextents<char, 2>(40,40)); map(10, 3) == -126
  80     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
  81         __required_span_size_is_representable(__ext),
  82         "layout_left::mapping extents ctor: product of extents must be representable as index_type.");
  83   }
  84
  85   template <class _OtherExtents>
  86     requires(is_constructible_v<extents_type, _OtherExtents>)
  87   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherExtents, extents_type>)
  88       mapping(const mapping<_OtherExtents>& __other) noexcept
  89       : __extents_(__other.extents()) {
  90     // not catching this could lead to out-of-bounds access later when used inside mdspan
  91     // mapping<dextents<char, 2>> map(mapping<dextents<int, 2>>(dextents<int, 2>(40,40))); map(10, 3) == -126
  92     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
  93         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
  94         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
  95   }
  96
  97   template <class _OtherExtents>
  98     requires(is_constructible_v<extents_type, _OtherExtents> && _OtherExtents::rank() <= 1)
  99   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherExtents, extents_type>)
 100       mapping(const layout_right::mapping<_OtherExtents>& __other) noexcept
 101       : __extents_(__other.extents()) {
 102     // not catching this could lead to out-of-bounds access later when used inside mdspan
 103     // Note: since this is constraint to rank 1, extents itself would catch the invalid conversion first
 104     //       and thus this assertion should never be triggered, but keeping it here for consistency
 105     // layout_left::mapping<dextents<char, 1>> map(
 106     //           layout_right::mapping<dextents<unsigned, 1>>(dextents<unsigned, 1>(200))); map.extents().extent(0) ==
 107     //           -56
 108     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 109         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
 110         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
 111   }
 112
 113 // FIXME: add when we add other layouts
 114 #  if 0
 115     template<class _OtherExtents>
 116       constexpr explicit(extents_type::rank() > 0)
 117         mapping(const layout_stride::mapping_<OtherExtents>&) noexcept;
 118 #  endif
 119
 120   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
 121
 122   // [mdspan.layout.left.obs], observers
 123   _LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __extents_; }
 124
 125   _LIBCPP_HIDE_FROM_ABI constexpr index_type required_span_size() const noexcept {
 126     index_type __size = 1;
 127     for (size_t __r = 0; __r < extents_type::rank(); __r++)
 128       __size *= __extents_.extent(__r);
 129     return __size;
 130   }
 131
 132   template <class... _Indices>
 133     requires((sizeof...(_Indices) == extents_type::rank()) && (is_convertible_v<_Indices, index_type> && ...) &&
 134              (is_nothrow_constructible_v<index_type, _Indices> && ...))
 135   _LIBCPP_HIDE_FROM_ABI constexpr index_type operator()(_Indices... __idx) const noexcept {
 136     // Mappings are generally meant to be used for accessing allocations and are meant to guarantee to never
 137     // return a value exceeding required_span_size(), which is used to know how large an allocation one needs
 138     // Thus, this is a canonical point in multi-dimensional data structures to make invalid element access checks
 139     // However, mdspan does check this on its own, so for now we avoid double checking in hardened mode
 140     _LIBCPP_ASSERT(__mdspan_detail::__is_multidimensional_index_in(__extents_, __idx...),
 141                    "layout_left::mapping: out of bounds indexing");
 142     array<index_type, extents_type::rank()> __idx_a{static_cast<index_type>(__idx)...};
 143     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 144       index_type __res = 0;
 145       ((__res = __idx_a[extents_type::rank() - 1 - _Pos] + __extents_.extent(extents_type::rank() - 1 - _Pos) * __res),
 146        ...);
 147       return __res;
 148     }(make_index_sequence<sizeof...(_Indices)>());
 149   }
 150
 151   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return true; }
 152   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept { return true; }
 153   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept { return true; }
 154
 155   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_unique() noexcept { return true; }
 156   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_exhaustive() noexcept { return true; }
 157   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_strided() noexcept { return true; }
 158
 159   _LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const noexcept
 160     requires(extents_type::rank() > 0)
 161   {
 162     // While it would be caught by extents itself too, using a too large __r
 163     // is functionally an out of bounds access on the stored information needed to compute strides
 164     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 165         __r < extents_type::rank(), "layout_left::mapping::stride(): invalid rank index");
 166     index_type __s = 1;
 167     for (rank_type __i = 0; __i < __r; __i++)
 168       __s *= __extents_.extent(__i);
 169     return __s;
 170   }
 171
 172   template <class _OtherExtents>
 173     requires(_OtherExtents::rank() == extents_type::rank())
 174   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
 175   operator==(const mapping& __lhs, const mapping<_OtherExtents>& __rhs) noexcept {
 176     return __lhs.extents() == __rhs.extents();
 177   }
 178
 179 private:
 180   _LIBCPP_NO_UNIQUE_ADDRESS extents_type __extents_{};
 181 };
 182
 183 #endif // _LIBCPP_STD_VER >= 23
 184
 185 _LIBCPP_END_NAMESPACE_STD
 186
 187 _LIBCPP_POP_MACROS
 188
 189 #endif // _LIBCPP___MDSPAN_LAYOUT_LEFT_H