[PATCH v4 5/5] libstdc++: Implement submdspan_mapping for layout_right_padded. [PR110352]
Luc Grosheintz
luc.grosheintz@gmail.com
Thu Dec 4 21:28:46 GMT 2025
Implements submdspan for layout_right_padded as described in P3663.
PR libstdc++/110352
libstdc++-v3/ChangeLog:
* include/std/mdspan (layout_right_padded::submdspan_mapping):
New friend method.
* testsuite/23_containers/mdspan/submdspan/submdspan.cc:
Instantiate test for layout_right_padded.
* testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc:
Ditto.
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
---
libstdc++-v3/include/std/mdspan | 45 +++++++++++++++++++
.../mdspan/submdspan/submdspan.cc | 7 ++-
.../mdspan/submdspan/submdspan_mapping.cc | 4 ++
3 files changed, 54 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 21dbe6def22..269522f4a5a 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -1353,40 +1353,76 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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 _SubRank, size_t _Nm>
static consteval bool
_S_is_unpadded_submdspan(span<const _SliceKind, _Nm> __slice_kinds)
{
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<_SubRank>(span(__rev_slice_kinds));
}
};
+ template<>
+ struct _SubMdspanMapping<_LayoutSide::__right, true>
+ {
+ 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 - 1);
+ constexpr auto __sta_padstride
+ = __mdspan::__get_static_stride<_Mapping>();
+ if constexpr (__sta_padstride == dynamic_extent
+ || !__mdspan::__all_static(__sta_exts))
+ return dynamic_extent;
+ else
+ return __sta_padstride * __mdspan::__fwd_prod(__sta_exts);
+ }
+
+ template<size_t _SubRank, size_t _Nm>
+ static consteval bool
+ _S_is_unpadded_submdspan(span<const _SliceKind, _Nm> __slice_kinds)
+ {
+ if constexpr (_SubRank == 1)
+ return __slice_kinds[_Nm - 1] == _SliceKind::__unit_strided_slice
+ || __slice_kinds[_Nm - 1] == _SliceKind::__full;
+ else
+ return false;
+ }
+ };
+
+
template<typename _Mapping>
constexpr auto
__submdspan_mapping_impl(const _Mapping& __mapping)
{ return submdspan_mapping_result{__mapping, 0}; }
template<typename _Mapping, typename... _Slices>
requires (sizeof...(_Slices) > 0)
constexpr auto
__submdspan_mapping_impl(const _Mapping& __mapping, _Slices... __slices)
{
constexpr auto __side = __mdspan::__mapping_side<_Mapping>();
using _Trait = _SubMdspanMapping<__side, __is_padded_mapping<_Mapping>>;
constexpr auto __slice_kinds = __mdspan::__make_slice_kind_array<_Slices...>();
auto __offset = __mdspan::__suboffset(__mapping, __slices...);
auto __sub_exts = __mdspan::__subextents(__mapping.extents(), __slices...);
using _SubExts = decltype(__sub_exts);
constexpr auto __sub_rank = _SubExts::rank();
if constexpr (__sub_rank == 0)
return submdspan_mapping_result{
@@ -2748,40 +2784,49 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
if constexpr (_S_rank <= 1)
return 1;
else if (__r == _S_rank - 1)
return 1;
else if (__r == _S_rank - 2)
return _M_padstride();
else
return static_cast<index_type>(
static_cast<size_t>(_M_padstride()) *
static_cast<size_t>(__mdspan::__fwd_prod(
extents(), __r + 1, _S_rank - 1)));
}
template<typename _RightPaddedMapping>
requires(__mdspan::__is_right_padded_mapping<_RightPaddedMapping>
&& _RightPaddedMapping::extents_type::rank() == _S_rank)
friend constexpr bool
operator==(const mapping& __self, const _RightPaddedMapping& __other)
noexcept
{ return __self._M_storage._M_equal(__other); }
+
+#if __glibcxx_submdspan
+ private:
+ template<__mdspan::__acceptable_slice_type<index_type>... _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
};
#endif // __glibcxx_padded_layouts
template<typename _ElementType>
struct default_accessor
{
static_assert(!is_array_v<_ElementType>,
"ElementType must not be an array type");
static_assert(!is_abstract_v<_ElementType>,
"ElementType must not be an abstract class type");
using offset_policy = default_accessor;
using element_type = _ElementType;
using reference = element_type&;
using data_handle_type = element_type*;
constexpr
default_accessor() noexcept = default;
template<typename _OElementType>
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan.cc b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan.cc
index 927b5d06c6b..f8382847fe3 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan.cc
@@ -348,27 +348,30 @@ template<typename Layout>
};
run(std::extents(3, 5, 7));
run(std::extents<int, 3, 5, 7>{});
return true;
}
template<typename Layout>
constexpr bool
test_all()
{
test_all_cheap<Layout>();
test_all_expensive<Layout>();
return true;
}
int
main()
{
test_all<std::layout_left>();
+ test_all<std::layout_right>();
+ test_all<std::layout_stride>();
test_all<std::layout_left_padded<1>>();
test_all<std::layout_left_padded<8>>();
test_all<std::layout_left_padded<dyn>>();
- test_all<std::layout_right>();
- test_all<std::layout_stride>();
+ test_all<std::layout_right_padded<1>>();
+ test_all<std::layout_right_padded<8>>();
+ test_all<std::layout_right_padded<dyn>>();
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 50836968a06..efd71d10f9d 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc
@@ -273,25 +273,29 @@ template<typename Layout>
static_assert(test_layout_common_return_types<Layout>());
test_layout_padded_return_types<Layout>();
static_assert(test_layout_padded_return_types<Layout>());
test_layout_padded_padding_value<Layout>();
static_assert(test_layout_padded_padding_value<Layout>());
return true;
}
int
main()
{
test_return_types_unpadded_all<std::layout_left>();
test_return_types_unpadded_all<std::layout_right>();
test_return_types_padded_all<std::layout_left_padded<1>>();
test_return_types_padded_all<std::layout_left_padded<2>>();
test_return_types_padded_all<std::layout_left_padded<dyn>>();
+ test_return_types_padded_all<std::layout_right_padded<1>>();
+ test_return_types_padded_all<std::layout_right_padded<2>>();
+ test_return_types_padded_all<std::layout_right_padded<dyn>>();
+
test_layout_stride_return_types();
static_assert(test_layout_stride_return_types());
return 0;
}
--
2.52.0
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