[libc++] mdspan - implement layout_stride

libcxx/docs/FeatureTestMacroTable.rst

@@ -332,7 +332,7 @@ Status
     --------------------------------------------------- -----------------
     ``__cpp_lib_is_scoped_enum``                        ``202011L``
     --------------------------------------------------- -----------------
-    ``__cpp_lib_mdspan``                                *unimplemented*
+    ``__cpp_lib_mdspan``                                ``202207L``
     --------------------------------------------------- -----------------
     ``__cpp_lib_move_only_function``                    *unimplemented*
     --------------------------------------------------- -----------------

libcxx/docs/Status/Cxx23.rst

@@ -40,7 +40,6 @@ Paper Status
 
 .. note::
 
-   .. [#note-P0009R18] P0009R18: ``extents``, ``dextents``, ``layout_left``, ``layout_right``, and ``default_accessor`` are implemented.
    .. [#note-P0533R9] P0533R9: ``isfinite``, ``isinf``, ``isnan`` and ``isnormal`` are implemented.
    .. [#note-P1413R3] P1413R3: ``std::aligned_storage_t`` and ``std::aligned_union_t`` are marked deprecated, but
       clang doesn't issue a diagnostic for deprecated using template declarations.

libcxx/docs/Status/Cxx23Papers.csv

@@ -51,7 +51,7 @@
 "`P2442R1 <https://wg21.link/P2442R1>`__","LWG","Windowing range adaptors: ``views::chunk`` and ``views::slide``","February 2022","","","|ranges|"
 "`P2443R1 <https://wg21.link/P2443R1>`__","LWG","``views::chunk_by``","February 2022","|Complete|","18.0","|ranges|"
 "","","","","","",""
-"`P0009R18 <https://wg21.link/P0009R18>`__","LWG","mdspan: A Non-Owning Multidimensional Array Reference","July 2022","|In progress| [#note-P0009R18]_",""
+"`P0009R18 <https://wg21.link/P0009R18>`__","LWG","mdspan: A Non-Owning Multidimensional Array Reference","July 2022","|Complete|","18.0"
 "`P0429R9 <https://wg21.link/P0429R9>`__","LWG","A Standard ``flat_map``","July 2022","",""
 "`P1169R4 <https://wg21.link/P1169R4>`__","LWG","``static operator()``","July 2022","|Complete|","16.0"
 "`P1222R4 <https://wg21.link/P1222R4>`__","LWG","A Standard ``flat_set``","July 2022","",""
@@ -89,9 +89,9 @@
 "`P2549R1 <https://wg21.link/P2549R1>`__","LWG","``std::unexpected`` should have ``error()`` as member accessor","July 2022","|Complete|","16.0"
 "`P2585R0 <https://wg21.link/P2585R0>`__","LWG","Improving default container formatting","July 2022","|Complete|","17.0"
 "`P2590R2 <https://wg21.link/P2590R2>`__","LWG","Explicit lifetime management","July 2022","",""
-"`P2599R2 <https://wg21.link/P2599R2>`__","LWG","``mdspan::size_type`` should be ``index_type``","July 2022","",""
-"`P2604R0 <https://wg21.link/P2604R0>`__","LWG","mdspan: rename pointer and contiguous","July 2022","",""
-"`P2613R1 <https://wg21.link/P2613R1>`__","LWG","Add the missing ``empty`` to ``mdspan``","July 2022","",""
+"`P2599R2 <https://wg21.link/P2599R2>`__","LWG","``mdspan::size_type`` should be ``index_type``","July 2022","|Complete|","18.0"
+"`P2604R0 <https://wg21.link/P2604R0>`__","LWG","mdspan: rename pointer and contiguous","July 2022","|Complete|","18.0"
+"`P2613R1 <https://wg21.link/P2613R1>`__","LWG","Add the missing ``empty`` to ``mdspan``","July 2022","|Complete|","18.0"
 "","","","","","",""
 "`P1202R5 <https://wg21.link/P1202R5>`__","LWG", "Asymmetric Fences", "November 2022","","","|concurrency TS|"
 "`P1264R2 <https://wg21.link/P1264R2>`__","LWG", "Revising the wording of ``stream`` input operations", "November 2022","|Complete|","9.0",""

libcxx/include/CMakeLists.txt

@@ -508,6 +508,7 @@ set(files
   __mdspan/extents.h
   __mdspan/layout_left.h
   __mdspan/layout_right.h
+  __mdspan/layout_stride.h
   __mdspan/mdspan.h
   __memory/addressof.h
   __memory/align.h

libcxx/include/__fwd/mdspan.h

@@ -42,14 +42,11 @@ struct layout_right {
   class mapping;
 };
 
-/*
-// Will be implemented with follow on revision
 // Layout policy with a unique mapping where strides are arbitrary
 struct layout_stride {
-  template<class Extents>
-    class mapping;
+  template <class _Extents>
+  class mapping;
 };
-*/
 
 #endif // _LIBCPP_STD_VER >= 23
 

libcxx/include/__mdspan/layout_left.h

@@ -110,12 +110,27 @@ class layout_left::mapping {
         "layout_left::mapping converting ctor: other.required_span_size() must be representable as index_type.");
   }
 
-// FIXME: add when we add other layouts
-#  if 0
-    template<class _OtherExtents>
-      constexpr explicit(extents_type::rank() > 0)
-        mapping(const layout_stride::mapping_<OtherExtents>&) noexcept;
-#  endif
+  template <class _OtherExtents>
+    requires(is_constructible_v<extents_type, _OtherExtents>)
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit(extents_type::rank() > 0)
+      mapping(const layout_stride::mapping<_OtherExtents>& __other) noexcept
+      : __extents_(__other.extents()) {
+    if constexpr (extents_type::rank() > 0) {
+      _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+          ([&]() {
+            using _CommonType = common_type_t<typename extents_type::index_type, typename _OtherExtents::index_type>;
+            for (rank_type __r = 0; __r < extents_type::rank(); __r++)
+              if (static_cast<_CommonType>(stride(__r)) != static_cast<_CommonType>(__other.stride(__r)))
+                return false;
+            return true;
+          }()),
+          "layout_left::mapping from layout_stride ctor: strides are not compatible with layout_left.");
+      _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+          __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
+          "layout_left::mapping from layout_stride ctor: other.required_span_size() must be representable as "
+          "index_type.");
+    }
+  }
 
   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
 

libcxx/include/__mdspan/layout_right.h

@@ -109,12 +109,27 @@ class layout_right::mapping {
         "layout_right::mapping converting ctor: other.required_span_size() must be representable as index_type.");
   }
 
-// FIXME: add when we add other layouts
-#  if 0
-    template<class _OtherExtents>
-      constexpr explicit(extents_type::rank() > 0)
-        mapping(const layout_stride::mapping_<OtherExtents>&) noexcept;
-#  endif
+  template <class _OtherExtents>
+    requires(is_constructible_v<extents_type, _OtherExtents>)
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit(extents_type::rank() > 0)
+      mapping(const layout_stride::mapping<_OtherExtents>& __other) noexcept
+      : __extents_(__other.extents()) {
+    if constexpr (extents_type::rank() > 0) {
+      _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+          ([&]() {
+            using _CommonType = common_type_t<typename extents_type::index_type, typename _OtherExtents::index_type>;
+            for (rank_type __r = 0; __r < extents_type::rank(); __r++)
+              if (static_cast<_CommonType>(stride(__r)) != static_cast<_CommonType>(__other.stride(__r)))
+                return false;
+            return true;
+          }()),
+          "layout_right::mapping from layout_stride ctor: strides are not compatible with layout_right.");
+      _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+          __mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
+          "layout_right::mapping from layout_stride ctor: other.required_span_size() must be representable as "
+          "index_type.");
+    }
+  }
 
   _LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;