On Mon, Dec 8, 2025 at 9:22 PM Luc Grosheintz <[email protected]> wrote:
> Adds submdspan_mapping for layout_right as described in P3663. > > PR libstdc++/110352 > > libstdc++-v3/ChangeLog: > > * include/std/mdspan (layout_right::mapping::submdspan_mapping): > New > friend function. > * testsuite/23_containers/mdspan/submdspan/selections/right.cc: > Instantiate tests for layout_right. > * testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc: > Ditto. > * testsuite/23_containers/mdspan/submdspan/submdspan_neg.cc: > Ditto. > > Signed-off-by: Luc Grosheintz <[email protected]> > --- > LGTM > libstdc++-v3/include/std/mdspan | 40 +++++++++++++++++++ > .../mdspan/submdspan/selections/right.cc | 9 +++++ > .../mdspan/submdspan/submdspan_mapping.cc | 6 +++ > .../mdspan/submdspan/submdspan_neg.cc | 9 +++++ > 4 files changed, 64 insertions(+) > create mode 100644 > libstdc++-v3/testsuite/23_containers/mdspan/submdspan/selections/right.cc > > diff --git a/libstdc++-v3/include/std/mdspan > b/libstdc++-v3/include/std/mdspan > index 4c004335289..c962d0e0cd3 100644 > --- a/libstdc++-v3/include/std/mdspan > +++ b/libstdc++-v3/include/std/mdspan > @@ -1303,6 +1303,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > { return __mdspan::__is_block(__slice_kinds, __sub_rank); } > }; > > + template<> > + struct _SubMdspanMapping<_LayoutSide::__right> > + { > + using _Layout = layout_right; > + template<size_t _Pad> using _PaddedLayout = > layout_right_padded<_Pad>; > + > + template<typename _Mapping, size_t _Us> > + static consteval size_t > + _S_pad() > + { > + using _Extents = typename _Mapping::extents_type; > + constexpr auto __rank = _Extents::rank(); > + constexpr auto __sta_exts > + = __mdspan::__static_extents<_Extents>(_Us + 1, __rank); > + if constexpr (!__mdspan::__all_static(__sta_exts)) > + return dynamic_extent; > + else > + return __fwd_prod(__sta_exts); > + } > + > + template<size_t _Nm> > + static consteval bool > + _S_is_unpadded_submdspan(span<const _SliceKind, _Nm> > __slice_kinds, > + size_t __sub_rank) > + { > + auto __rev_slice_kinds = array<_SliceKind, _Nm>{}; > + for(size_t __i = 0; __i < _Nm; ++__i) > + __rev_slice_kinds[__i] = __slice_kinds[_Nm - 1 - __i]; > + return __mdspan::__is_block(span(__rev_slice_kinds), > __sub_rank); > + } > + }; > + > template<typename _Mapping> > constexpr auto > __submdspan_mapping_impl(const _Mapping& __mapping) > @@ -1678,6 +1710,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > __glibcxx_assert(__mdspan::__is_representable_extents(_M_extents)); > } > > +#if __glibcxx_submdspan > + template<typename... _Slices> > + requires (extents_type::rank() == sizeof...(_Slices)) > + friend constexpr auto > + submdspan_mapping(const mapping& __mapping, _Slices... __slices) > + { return __mdspan::__submdspan_mapping_impl(__mapping, > __slices...); } > +#endif // __glibcxx_submdspan > + > [[no_unique_address]] extents_type _M_extents{}; > }; > > diff --git > a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/selections/right.cc > b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/selections/right.cc > new file mode 100644 > index 00000000000..25570721072 > --- /dev/null > +++ > b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/selections/right.cc > @@ -0,0 +1,9 @@ > +// { dg-do run { target c++26 } } > +#include "testcases.h" > + > +int > +main() > +{ > + test_all<std::layout_right>(); > + return 0; > +} > diff --git > a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc > b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc > index a37d3cd588f..cc832cdb415 100644 > --- > a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc > +++ > b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc > @@ -129,8 +129,14 @@ main() > test_layout_unpadded_return_types<std::layout_left>(); > static_assert(test_layout_unpadded_return_types<std::layout_left>()); > > + test_layout_unpadded_return_types<std::layout_right>(); > + static_assert(test_layout_unpadded_return_types<std::layout_right>()); > + > test_layout_unpadded_padding_value<std::layout_left>(); > static_assert(test_layout_unpadded_padding_value<std::layout_left>()); > + > + test_layout_unpadded_padding_value<std::layout_right>(); > + static_assert(test_layout_unpadded_padding_value<std::layout_right>()); > return 0; > } > > diff --git > a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_neg.cc > b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_neg.cc > index 1fc10a832eb..15b9b2e71ec 100644 > --- > a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_neg.cc > +++ > b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_neg.cc > @@ -24,6 +24,7 @@ template<typename Layout> > return true; > } > static_assert(test_int_under<std::layout_left>()); // { dg-error > "expansion of" } > +static_assert(test_int_under<std::layout_right>()); // { dg-error > "expansion of" } > > template<typename Layout> > constexpr bool > @@ -33,6 +34,7 @@ template<typename Layout> > return true; > } > static_assert(test_int_over<std::layout_left>()); // { dg-error > "expansion of" } > +static_assert(test_int_over<std::layout_right>()); // { dg-error > "expansion of" } > > template<typename Layout> > constexpr bool > @@ -42,6 +44,7 @@ template<typename Layout> > return true; > } > static_assert(test_tuple_under<std::layout_left>()); // { dg-error > "expansion of" } > +static_assert(test_tuple_under<std::layout_right>()); // { dg-error > "expansion of" } > > template<typename Layout> > constexpr bool > @@ -51,6 +54,7 @@ template<typename Layout> > return true; > } > static_assert(test_tuple_reversed<std::layout_left>()); // { dg-error > "expansion of" } > +static_assert(test_tuple_reversed<std::layout_right>()); // { dg-error > "expansion of" } > > template<typename Layout> > constexpr bool > @@ -60,6 +64,7 @@ template<typename Layout> > return true; > } > static_assert(test_tuple_over<std::layout_left>()); // { dg-error > "expansion of" } > +static_assert(test_tuple_over<std::layout_right>()); // { dg-error > "expansion of" } > > template<typename Layout> > constexpr bool > @@ -69,6 +74,7 @@ template<typename Layout> > return true; > } > static_assert(test_strided_slice_zero<std::layout_left>()); // { > dg-error "expansion of" } > +static_assert(test_strided_slice_zero<std::layout_right>()); // { > dg-error "expansion of" } > > template<typename Layout> > constexpr bool > @@ -78,6 +84,7 @@ template<typename Layout> > return true; > } > static_assert(test_strided_slice_offset_under<std::layout_left>()); // > { dg-error "expansion of" } > +static_assert(test_strided_slice_offset_under<std::layout_right>()); // > { dg-error "expansion of" } > > template<typename Layout> > constexpr bool > @@ -87,6 +94,7 @@ template<typename Layout> > return true; > } > static_assert(test_strided_slice_offset_over<std::layout_left>()); // { > dg-error "expansion of" } > +static_assert(test_strided_slice_offset_over<std::layout_right>()); // { > dg-error "expansion of" } > > template<typename Layout> > constexpr bool > @@ -96,6 +104,7 @@ template<typename Layout> > return true; > } > static_assert(test_strided_slice_extent_over<std::layout_left>()); // { > dg-error "expansion of" } > +static_assert(test_strided_slice_extent_over<std::layout_right>()); // { > dg-error "expansion of" } > > // { dg-prune-output "static assertion failed" } > // { dg-prune-output "__glibcxx_assert_fail" } > -- > 2.52.0 > >
