On Wed, 4 Jun 2025 at 16:10, Luc Grosheintz <[email protected]> wrote:
>
> 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 <[email protected]>
OK for trunk
> ---
> 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 4c80438dbd6..8ab7a1a52fb 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 8ea57132a2a..fe1407d71da 100644
> --- a/libstdc++-v3/src/c++23/std.cc.in
> +++ b/libstdc++-v3/src/c++23/std.cc.in
> @@ -1845,6 +1845,7 @@ export namespace std
> {
> using std::extents;
> using std::layout_left;
> + using std::layout_right;
> // FIXME layout_*, default_accessor and mdspan
> }
> #endif
> --
> 2.49.0
>
