[gcc r16-1469] libstdc++: Implement layout_right from mdspan.
Tomasz Kaminski
tkaminsk@gcc.gnu.org
Thu Jun 12 09:48:50 GMT 2025
https://gcc.gnu.org/g:f40f96bcf251dcb4b13b87e1569bb144dd53ebe0
commit r16-1469-gf40f96bcf251dcb4b13b87e1569bb144dd53ebe0
Author: Luc Grosheintz <luc.grosheintz@gmail.com>
Date: Wed Jun 4 16:58:49 2025 +0200
libstdc++: Implement layout_right from mdspan.
Implement the parts of layout_left that depend on layout_right; and the
parts of layout_right that don't depend on layout_stride.
libstdc++-v3/ChangeLog:
* include/std/mdspan (layout_right): New class.
* src/c++23/std.cc.in: Add layout_right.
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Diff:
---
libstdc++-v3/include/std/mdspan | 153 ++++++++++++++++++++++++++++++++++++++-
libstdc++-v3/src/c++23/std.cc.in | 1 +
2 files changed, 153 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 4c80438dbd62..8ab7a1a52fbe 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -409,6 +409,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
class mapping;
};
+ struct layout_right
+ {
+ template<typename _Extents>
+ class mapping;
+ };
+
namespace __mdspan
{
template<typename _Tp>
@@ -501,7 +507,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_Mapping>;
template<typename _Mapping>
- concept __standardized_mapping = __mapping_of<layout_left, _Mapping>;
+ concept __standardized_mapping = __mapping_of<layout_left, _Mapping>
+ || __mapping_of<layout_right, _Mapping>;
// A tag type to create internal ctors.
class __internal_ctor
@@ -539,6 +546,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: mapping(__other.extents(), __mdspan::__internal_ctor{})
{ }
+ template<typename _OExtents>
+ requires (extents_type::rank() <= 1)
+ && is_constructible_v<extents_type, _OExtents>
+ constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
+ mapping(const layout_right::mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { }
+
constexpr mapping&
operator=(const mapping&) noexcept = default;
@@ -605,6 +620,142 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
[[no_unique_address]] extents_type _M_extents{};
};
+ namespace __mdspan
+ {
+ template<typename _Extents, typename... _Indices>
+ constexpr typename _Extents::index_type
+ __linear_index_right(const _Extents& __exts, _Indices... __indices)
+ noexcept
+ {
+ using _IndexType = typename _Extents::index_type;
+ array<_IndexType, sizeof...(__indices)> __ind_arr{__indices...};
+ _IndexType __res = 0;
+ if constexpr (sizeof...(__indices) > 0)
+ {
+ _IndexType __mult = 1;
+ auto __update = [&, __pos = __exts.rank()](_IndexType) mutable
+ {
+ --__pos;
+ __res += __ind_arr[__pos] * __mult;
+ __mult *= __exts.extent(__pos);
+ };
+ (__update(__indices), ...);
+ }
+ return __res;
+ }
+ }
+
+ template<typename _Extents>
+ class layout_right::mapping
+ {
+ public:
+ using extents_type = _Extents;
+ using index_type = typename extents_type::index_type;
+ using size_type = typename extents_type::size_type;
+ using rank_type = typename extents_type::rank_type;
+ using layout_type = layout_right;
+
+ static_assert(__mdspan::__representable_size<extents_type, index_type>,
+ "The size of extents_type must be representable as index_type");
+
+ constexpr
+ mapping() noexcept = default;
+
+ constexpr
+ mapping(const mapping&) noexcept = default;
+
+ constexpr
+ mapping(const extents_type& __extents) noexcept
+ : _M_extents(__extents)
+ { __glibcxx_assert(__mdspan::__is_representable_extents(_M_extents)); }
+
+ template<typename _OExtents>
+ requires is_constructible_v<extents_type, _OExtents>
+ constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
+ mapping(const mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { }
+
+ template<class _OExtents>
+ requires (extents_type::rank() <= 1)
+ && is_constructible_v<extents_type, _OExtents>
+ constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
+ mapping(const layout_left::mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { }
+
+ constexpr mapping&
+ operator=(const mapping&) noexcept = default;
+
+ constexpr const extents_type&
+ extents() const noexcept { return _M_extents; }
+
+ constexpr index_type
+ required_span_size() const noexcept
+ { return __mdspan::__fwd_prod(_M_extents, extents_type::rank()); }
+
+ template<__mdspan::__valid_index_type<index_type>... _Indices>
+ requires (sizeof...(_Indices) == extents_type::rank())
+ constexpr index_type
+ operator()(_Indices... __indices) const noexcept
+ {
+ return __mdspan::__linear_index_right(
+ _M_extents, static_cast<index_type>(__indices)...);
+ }
+
+ static constexpr bool
+ is_always_unique() noexcept
+ { return true; }
+
+ static constexpr bool
+ is_always_exhaustive() noexcept
+ { return true; }
+
+ static constexpr bool
+ is_always_strided() noexcept
+ { return true; }
+
+ static constexpr bool
+ is_unique() noexcept
+ { return true; }
+
+ static constexpr bool
+ is_exhaustive() noexcept
+ { return true; }
+
+ static constexpr bool
+ is_strided() noexcept
+ { return true; }
+
+ constexpr index_type
+ stride(rank_type __i) const noexcept
+ requires (extents_type::rank() > 0)
+ {
+ __glibcxx_assert(__i < extents_type::rank());
+ return __mdspan::__rev_prod(_M_extents, __i);
+ }
+
+ template<typename _OExtents>
+ requires (extents_type::rank() == _OExtents::rank())
+ friend constexpr bool
+ operator==(const mapping& __self, const mapping<_OExtents>& __other)
+ noexcept
+ { return __self.extents() == __other.extents(); }
+
+ private:
+ template<typename _OExtents>
+ constexpr explicit
+ mapping(const _OExtents& __oexts, __mdspan::__internal_ctor) noexcept
+ : _M_extents(__oexts)
+ {
+ static_assert(__mdspan::__representable_size<_OExtents, index_type>,
+ "The size of OtherExtents must be representable as index_type");
+ __glibcxx_assert(__mdspan::__is_representable_extents(_M_extents));
+ }
+
+ [[no_unique_address]] extents_type _M_extents{};
+ };
+
_GLIBCXX_END_NAMESPACE_VERSION
}
#endif
diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/std.cc.in
index fd9a07151dcc..5af0f7ef5e2b 100644
--- a/libstdc++-v3/src/c++23/std.cc.in
+++ b/libstdc++-v3/src/c++23/std.cc.in
@@ -1841,6 +1841,7 @@ export namespace std
{
using std::extents;
using std::layout_left;
+ using std::layout_right;
// FIXME layout_*, default_accessor and mdspan
}
#endif
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