CHECKPOINT

submdspan builds now when submdspan_mapping is called with
canonical slices, but the submdspan test fails.

Investigate whether this is a bug in the implementation.

Author: mhoemmen

include/experimental/__p2630_bits/submdspan.hpp

@@ -28,22 +28,16 @@ submdspan(const mdspan<ElementType, Extents, LayoutPolicy, AccessorPolicy> &src,
           SliceSpecifiers... slices) {
 
 #if defined(MDSPAN_ENABLE_P3663)
-  [[maybe_unused]] auto [...canonical_slices] = submdspan_canonicalize_slices(src.extents(), slices...);
+  auto [...canonical_slices] = submdspan_canonicalize_slices(src.extents(), slices...);
   static_assert(sizeof...(canonical_slices) == sizeof...(slices));
-  [[maybe_unused]] auto sub_map_result = submdspan_mapping(src.mapping(), canonical_slices...);
-
-#if 0
   // TODO FIX IN PROPOSAL: [canonical_]slices (incorrect formatting).
   auto sub_map_result = submdspan_mapping(src.mapping(), canonical_slices...);
   // TODO FIX IN PROPOSAL: It's src.data_handle(), not src.data().
   // Missing "typename" before AccessorPolicy::offset_policy.
   return mdspan(src.accessor().offset(src.data_handle(), sub_map_result.offset),
                 sub_map_result.mapping,
                 typename AccessorPolicy::offset_policy(src.accessor()));  
-#endif // 0
-#endif
-
-//#else
+#else
   const auto sub_submdspan_mapping_result = submdspan_mapping(src.mapping(), slices...);
   // NVCC has a problem with the deduction so lets figure out the type
   using sub_mapping_t = std::remove_cv_t<decltype(sub_submdspan_mapping_result.mapping)>;
@@ -54,6 +48,6 @@ submdspan(const mdspan<ElementType, Extents, LayoutPolicy, AccessorPolicy> &src,
       src.accessor().offset(src.data_handle(), sub_submdspan_mapping_result.offset),
       sub_submdspan_mapping_result.mapping,
       sub_accessor_t(src.accessor()));
-//#endif
+#endif
 }
 } // namespace MDSPAN_IMPL_STANDARD_NAMESPACE

include/experimental/__p2630_bits/submdspan_mapping.hpp

@@ -132,13 +132,35 @@ MDSPAN_INLINE_FUNCTION constexpr auto construct_sub_strides(
        static_cast<index_type>(get<InvMapIdxs>(slices_stride_factor)))...}};
 }
 
+// NOTE Make the submdspan_mapping_impl functions recognize
+// strided_slice with compile-time stride 1 as a range slice.
+// Otherwise, they fall back to layout_stride::mapping.
+// This might be a bug in the pre-P3663 implementation.
+
+#if defined(MDSPAN_ENABLE_P3663)
+
+template<class SliceSpecifier, class IndexType>
+struct is_range_slice : std::false_type {};
+
+template<class IndexType>
+struct is_range_slice<full_extent_t, IndexType> : std::true_type {};
+
+template<class OffsetType, class ExtentType, auto Stride, class IndexType>
+struct is_range_slice<strided_slice<OffsetType, ExtentType, std::constant_wrapper<Stride>>, IndexType> {
+  static constexpr bool value = (std::constant_wrapper<Stride>{}() == IndexType(1));
+};
+
+#else
+
 template<class SliceSpecifier, class IndexType>
 struct is_range_slice {
   constexpr static bool value =
     std::is_same_v<SliceSpecifier, full_extent_t> ||
     index_pair_like<SliceSpecifier, IndexType>::value;
 };
 
+#endif // MDSPAN_ENABLE_P3663
+
 template<class SliceSpecifier, class IndexType>
 constexpr bool is_range_slice_v = is_range_slice<SliceSpecifier, IndexType>::value;