libcxx/include/__cxx03/__mdspan/layout_stride.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_STRIDE_H
  18 #define _LIBCPP___MDSPAN_LAYOUT_STRIDE_H
  19
  20 #include <__cxx03/__assert>
  21 #include <__cxx03/__config>
  22 #include <__cxx03/__fwd/mdspan.h>
  23 #include <__cxx03/__mdspan/extents.h>
  24 #include <__cxx03/__type_traits/is_constructible.h>
  25 #include <__cxx03/__type_traits/is_convertible.h>
  26 #include <__cxx03/__type_traits/is_nothrow_constructible.h>
  27 #include <__cxx03/__utility/as_const.h>
  28 #include <__cxx03/__utility/integer_sequence.h>
  29 #include <__cxx03/__utility/swap.h>
  30 #include <__cxx03/array>
  31 #include <__cxx03/cinttypes>
  32 #include <__cxx03/cstddef>
  33 #include <__cxx03/limits>
  34
  35 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  36 #  pragma GCC system_header
  37 #endif
  38
  39 _LIBCPP_PUSH_MACROS
  40 #include <__cxx03/__undef_macros>
  41
  42 _LIBCPP_BEGIN_NAMESPACE_STD
  43
  44 #if _LIBCPP_STD_VER >= 23
  45
  46 namespace __mdspan_detail {
  47 template <class _Layout, class _Mapping>
  48 constexpr bool __is_mapping_of =
  49     is_same_v<typename _Layout::template mapping<typename _Mapping::extents_type>, _Mapping>;
  50
  51 template <class _Mapping>
  52 concept __layout_mapping_alike = requires {
  53   requires __is_mapping_of<typename _Mapping::layout_type, _Mapping>;
  54   requires __is_extents_v<typename _Mapping::extents_type>;
  55   { _Mapping::is_always_strided() } -> same_as<bool>;
  56   { _Mapping::is_always_exhaustive() } -> same_as<bool>;
  57   { _Mapping::is_always_unique() } -> same_as<bool>;
  58   bool_constant<_Mapping::is_always_strided()>::value;
  59   bool_constant<_Mapping::is_always_exhaustive()>::value;
  60   bool_constant<_Mapping::is_always_unique()>::value;
  61 };
  62 } // namespace __mdspan_detail
  63
  64 template <class _Extents>
  65 class layout_stride::mapping {
  66 public:
  67   static_assert(__mdspan_detail::__is_extents<_Extents>::value,
  68                 "layout_stride::mapping template argument must be a specialization of extents.");
  69
  70   using extents_type = _Extents;
  71   using index_type   = typename extents_type::index_type;
  72   using size_type    = typename extents_type::size_type;
  73   using rank_type    = typename extents_type::rank_type;
  74   using layout_type  = layout_stride;
  75
  76 private:
  77   static constexpr rank_type __rank_ = extents_type::rank();
  78
  79   // Used for default construction check and mandates
  80   _LIBCPP_HIDE_FROM_ABI static constexpr bool __required_span_size_is_representable(const extents_type& __ext) {
  81     if constexpr (__rank_ == 0)
  82       return true;
  83
  84     index_type __prod = __ext.extent(0);
  85     for (rank_type __r = 1; __r < __rank_; __r++) {
  86       bool __overflowed = __builtin_mul_overflow(__prod, __ext.extent(__r), &__prod);
  87       if (__overflowed)
  88         return false;
  89     }
  90     return true;
  91   }
  92
  93   template <class _OtherIndexType>
  94   _LIBCPP_HIDE_FROM_ABI static constexpr bool
  95   __required_span_size_is_representable(const extents_type& __ext, span<_OtherIndexType, __rank_> __strides) {
  96     if constexpr (__rank_ == 0)
  97       return true;
  98
  99     index_type __size = 1;
 100     for (rank_type __r = 0; __r < __rank_; __r++) {
 101       // We can only check correct conversion of _OtherIndexType if it is an integral
 102       if constexpr (is_integral_v<_OtherIndexType>) {
 103         using _CommonType = common_type_t<index_type, _OtherIndexType>;
 104         if (static_cast<_CommonType>(__strides[__r]) > static_cast<_CommonType>(numeric_limits<index_type>::max()))
 105           return false;
 106       }
 107       if (__ext.extent(__r) == static_cast<index_type>(0))
 108         return true;
 109       index_type __prod     = (__ext.extent(__r) - 1);
 110       bool __overflowed_mul = __builtin_mul_overflow(__prod, static_cast<index_type>(__strides[__r]), &__prod);
 111       if (__overflowed_mul)
 112         return false;
 113       bool __overflowed_add = __builtin_add_overflow(__size, __prod, &__size);
 114       if (__overflowed_add)
 115         return false;
 116     }
 117     return true;
 118   }
 119
 120   // compute offset of a strided layout mapping
 121   template <class _StridedMapping>
 122   _LIBCPP_HIDE_FROM_ABI static constexpr index_type __offset(const _StridedMapping& __mapping) {
 123     if constexpr (_StridedMapping::extents_type::rank() == 0) {
 124       return static_cast<index_type>(__mapping());
 125     } else if (__mapping.required_span_size() == static_cast<typename _StridedMapping::index_type>(0)) {
 126       return static_cast<index_type>(0);
 127     } else {
 128       return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 129         return static_cast<index_type>(__mapping((_Pos ? 0 : 0)...));
 130       }(make_index_sequence<__rank_>());
 131     }
 132   }
 133
 134   // compute the permutation for sorting the stride array
 135   // we never actually sort the stride array
 136   _LIBCPP_HIDE_FROM_ABI constexpr void __bubble_sort_by_strides(array<rank_type, __rank_>& __permute) const {
 137     for (rank_type __i = __rank_ - 1; __i > 0; __i--) {
 138       for (rank_type __r = 0; __r < __i; __r++) {
 139         if (__strides_[__permute[__r]] > __strides_[__permute[__r + 1]]) {
 140           swap(__permute[__r], __permute[__r + 1]);
 141         } else {
 142           // if two strides are the same then one of the associated extents must be 1 or 0
 143           // both could be, but you can't have one larger than 1 come first
 144           if ((__strides_[__permute[__r]] == __strides_[__permute[__r + 1]]) &&
 145               (__extents_.extent(__permute[__r]) > static_cast<index_type>(1)))
 146             swap(__permute[__r], __permute[__r + 1]);
 147         }
 148       }
 149     }
 150   }
 151
 152   static_assert(extents_type::rank_dynamic() > 0 || __required_span_size_is_representable(extents_type()),
 153                 "layout_stride::mapping product of static extents must be representable as index_type.");
 154
 155 public:
 156   // [mdspan.layout.stride.cons], constructors
 157   _LIBCPP_HIDE_FROM_ABI constexpr mapping() noexcept : __extents_(extents_type()) {
 158     // Note the nominal precondition is covered by above static assert since
 159     // if rank_dynamic is != 0 required_span_size is zero for default construction
 160     if constexpr (__rank_ > 0) {
 161       index_type __stride = 1;
 162       for (rank_type __r = __rank_ - 1; __r > static_cast<rank_type>(0); __r--) {
 163         __strides_[__r] = __stride;
 164         __stride *= __extents_.extent(__r);
 165       }
 166       __strides_[0] = __stride;
 167     }
 168   }
 169
 170   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const mapping&) noexcept = default;
 171
 172   template <class _OtherIndexType>
 173     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
 174              is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
 175   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext, span<_OtherIndexType, __rank_> __strides) noexcept
 176       : __extents_(__ext), __strides_([&]<size_t... _Pos>(index_sequence<_Pos...>) {
 177           return __mdspan_detail::__possibly_empty_array<index_type, __rank_>{
 178               static_cast<index_type>(std::as_const(__strides[_Pos]))...};
 179         }(make_index_sequence<__rank_>())) {
 180     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 181         ([&]<size_t... _Pos>(index_sequence<_Pos...>) {
 182           // For integrals we can do a pre-conversion check, for other types not
 183           if constexpr (is_integral_v<_OtherIndexType>) {
 184             return ((__strides[_Pos] > static_cast<_OtherIndexType>(0)) && ... && true);
 185           } else {
 186             return ((static_cast<index_type>(__strides[_Pos]) > static_cast<index_type>(0)) && ... && true);
 187           }
 188         }(make_index_sequence<__rank_>())),
 189         "layout_stride::mapping ctor: all strides must be greater than 0");
 190     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 191         __required_span_size_is_representable(__ext, __strides),
 192         "layout_stride::mapping ctor: required span size is not representable as index_type.");
 193     if constexpr (__rank_ > 1) {
 194       _LIBCPP_ASSERT_UNCATEGORIZED(
 195           ([&]<size_t... _Pos>(index_sequence<_Pos...>) {
 196             // basically sort the dimensions based on strides and extents, sorting is represented in permute array
 197             array<rank_type, __rank_> __permute{_Pos...};
 198             __bubble_sort_by_strides(__permute);
 199
 200             // check that this permutations represents a growing set
 201             for (rank_type __i = 1; __i < __rank_; __i++)
 202               if (static_cast<index_type>(__strides[__permute[__i]]) <
 203                   static_cast<index_type>(__strides[__permute[__i - 1]]) * __extents_.extent(__permute[__i - 1]))
 204                 return false;
 205             return true;
 206           }(make_index_sequence<__rank_>())),
 207           "layout_stride::mapping ctor: the provided extents and strides lead to a non-unique mapping");
 208     }
 209   }
 210
 211   template <class _OtherIndexType>
 212     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
 213              is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
 214   _LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext,
 215                                           const array<_OtherIndexType, __rank_>& __strides) noexcept
 216       : mapping(__ext, span(__strides)) {}
 217
 218   template <class _StridedLayoutMapping>
 219     requires(__mdspan_detail::__layout_mapping_alike<_StridedLayoutMapping> &&
 220              is_constructible_v<extents_type, typename _StridedLayoutMapping::extents_type> &&
 221              _StridedLayoutMapping::is_always_unique() && _StridedLayoutMapping::is_always_strided())
 222   _LIBCPP_HIDE_FROM_ABI constexpr explicit(
 223       !(is_convertible_v<typename _StridedLayoutMapping::extents_type, extents_type> &&
 224         (__mdspan_detail::__is_mapping_of<layout_left, _StridedLayoutMapping> ||
 225          __mdspan_detail::__is_mapping_of<layout_right, _StridedLayoutMapping> ||
 226          __mdspan_detail::__is_mapping_of<layout_stride, _StridedLayoutMapping>)))
 227       mapping(const _StridedLayoutMapping& __other) noexcept
 228       : __extents_(__other.extents()), __strides_([&]<size_t... _Pos>(index_sequence<_Pos...>) {
 229           // stride() only compiles for rank > 0
 230           if constexpr (__rank_ > 0) {
 231             return __mdspan_detail::__possibly_empty_array<index_type, __rank_>{
 232                 static_cast<index_type>(__other.stride(_Pos))...};
 233           } else {
 234             return __mdspan_detail::__possibly_empty_array<index_type, 0>{};
 235           }
 236         }(make_index_sequence<__rank_>())) {
 237     // stride() only compiles for rank > 0
 238     if constexpr (__rank_ > 0) {
 239       _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 240           ([&]<size_t... _Pos>(index_sequence<_Pos...>) {
 241             return ((static_cast<index_type>(__other.stride(_Pos)) > static_cast<index_type>(0)) && ... && true);
 242           }(make_index_sequence<__rank_>())),
 243           "layout_stride::mapping converting ctor: all strides must be greater than 0");
 244     }
 245     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 246         __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
 247         "layout_stride::mapping converting ctor: other.required_span_size() must be representable as index_type.");
 248     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(static_cast<index_type>(0) == __offset(__other),
 249                                         "layout_stride::mapping converting ctor: base offset of mapping must be zero.");
 250   }
 251
 252   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
 253
 254   // [mdspan.layout.stride.obs], observers
 255   _LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __extents_; }
 256
 257   _LIBCPP_HIDE_FROM_ABI constexpr array<index_type, __rank_> strides() const noexcept {
 258     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 259       return array<index_type, __rank_>{__strides_[_Pos]...};
 260     }(make_index_sequence<__rank_>());
 261   }
 262
 263   _LIBCPP_HIDE_FROM_ABI constexpr index_type required_span_size() const noexcept {
 264     if constexpr (__rank_ == 0) {
 265       return static_cast<index_type>(1);
 266     } else {
 267       return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 268         if ((__extents_.extent(_Pos) * ... * 1) == 0)
 269           return static_cast<index_type>(0);
 270         else
 271           return static_cast<index_type>(
 272               static_cast<index_type>(1) +
 273               (((__extents_.extent(_Pos) - static_cast<index_type>(1)) * __strides_[_Pos]) + ... +
 274                static_cast<index_type>(0)));
 275       }(make_index_sequence<__rank_>());
 276     }
 277   }
 278
 279   template <class... _Indices>
 280     requires((sizeof...(_Indices) == __rank_) && (is_convertible_v<_Indices, index_type> && ...) &&
 281              (is_nothrow_constructible_v<index_type, _Indices> && ...))
 282   _LIBCPP_HIDE_FROM_ABI constexpr index_type operator()(_Indices... __idx) const noexcept {
 283     // Mappings are generally meant to be used for accessing allocations and are meant to guarantee to never
 284     // return a value exceeding required_span_size(), which is used to know how large an allocation one needs
 285     // Thus, this is a canonical point in multi-dimensional data structures to make invalid element access checks
 286     // However, mdspan does check this on its own, so for now we avoid double checking in hardened mode
 287     _LIBCPP_ASSERT_UNCATEGORIZED(__mdspan_detail::__is_multidimensional_index_in(__extents_, __idx...),
 288                                  "layout_stride::mapping: out of bounds indexing");
 289     return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 290       return ((static_cast<index_type>(__idx) * __strides_[_Pos]) + ... + index_type(0));
 291     }(make_index_sequence<sizeof...(_Indices)>());
 292   }
 293
 294   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return true; }
 295   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept { return false; }
 296   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept { return true; }
 297
 298   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_unique() noexcept { return true; }
 299   // The answer of this function is fairly complex in the case where one or more
 300   // extents are zero.
 301   // Technically it is meaningless to query is_exhaustive() in that case, but unfortunately
 302   // the way the standard defines this function, we can't give a simple true or false then.
 303   _LIBCPP_HIDE_FROM_ABI constexpr bool is_exhaustive() const noexcept {
 304     if constexpr (__rank_ == 0)
 305       return true;
 306     else {
 307       index_type __span_size = required_span_size();
 308       if (__span_size == static_cast<index_type>(0)) {
 309         if constexpr (__rank_ == 1)
 310           return __strides_[0] == 1;
 311         else {
 312           rank_type __r_largest = 0;
 313           for (rank_type __r = 1; __r < __rank_; __r++)
 314             if (__strides_[__r] > __strides_[__r_largest])
 315               __r_largest = __r;
 316           for (rank_type __r = 0; __r < __rank_; __r++)
 317             if (__extents_.extent(__r) == 0 && __r != __r_largest)
 318               return false;
 319           return true;
 320         }
 321       } else {
 322         return required_span_size() == [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 323           return (__extents_.extent(_Pos) * ... * static_cast<index_type>(1));
 324         }(make_index_sequence<__rank_>());
 325       }
 326     }
 327   }
 328   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_strided() noexcept { return true; }
 329
 330   // according to the standard layout_stride does not have a constraint on stride(r) for rank>0
 331   // it still has the precondition though
 332   _LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const noexcept {
 333     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__r < __rank_, "layout_stride::mapping::stride(): invalid rank index");
 334     return __strides_[__r];
 335   }
 336
 337   template <class _OtherMapping>
 338     requires(__mdspan_detail::__layout_mapping_alike<_OtherMapping> &&
 339              (_OtherMapping::extents_type::rank() == __rank_) && _OtherMapping::is_always_strided())
 340   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const mapping& __lhs, const _OtherMapping& __rhs) noexcept {
 341     if (__offset(__rhs))
 342       return false;
 343     if constexpr (__rank_ == 0)
 344       return true;
 345     else {
 346       return __lhs.extents() == __rhs.extents() && [&]<size_t... _Pos>(index_sequence<_Pos...>) {
 347         // avoid warning when comparing signed and unsigner integers and pick the wider of two types
 348         using _CommonType = common_type_t<index_type, typename _OtherMapping::index_type>;
 349         return ((static_cast<_CommonType>(__lhs.stride(_Pos)) == static_cast<_CommonType>(__rhs.stride(_Pos))) && ... &&
 350                 true);
 351       }(make_index_sequence<__rank_>());
 352     }
 353   }
 354
 355 private:
 356   _LIBCPP_NO_UNIQUE_ADDRESS extents_type __extents_{};
 357   _LIBCPP_NO_UNIQUE_ADDRESS __mdspan_detail::__possibly_empty_array<index_type, __rank_> __strides_{};
 358 };
 359
 360 #endif // _LIBCPP_STD_VER >= 23
 361
 362 _LIBCPP_END_NAMESPACE_STD
 363
 364 _LIBCPP_POP_MACROS
 365
 366 #endif // _LIBCPP___MDSPAN_LAYOUT_STRIDE_H