On Fri, May 30, 2025 at 6:47 PM Luc Grosheintz <luc.groshei...@gmail.com>
wrote:
> Implements the parts of layout_left that don't depend on any of the
> other layouts.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/mdspan (layout_left): New class.
> * src/c++23/std.cc.in: Add layout_left.
>
> Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
> ---
> libstdc++-v3/include/std/mdspan | 306 ++++++++++++++++++++++++++++++-
> libstdc++-v3/src/c++23/std.cc.in | 1 +
> 2 files changed, 306 insertions(+), 1 deletion(-)
>
LGTM. One very small formatting change, that does not need to be addressed,
if there will not be any feedback requiring changes in next patches.
>
> diff --git a/libstdc++-v3/include/std/mdspan
> b/libstdc++-v3/include/std/mdspan
> index 0f49b0e09a0..904856ebb4f 100644
> --- a/libstdc++-v3/include/std/mdspan
> +++ b/libstdc++-v3/include/std/mdspan
> @@ -144,6 +144,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { return __exts[__i]; });
> }
>
> + static constexpr span<const size_t>
> + _S_static_extents(size_t __begin, size_t __end) noexcept
> + {
> + return {_Extents.data() + __begin, _Extents.data() + __end};
> + }
> +
> + constexpr span<const _IndexType>
> + _M_dynamic_extents(size_t __begin, size_t __end) const noexcept
> + requires (_Extents.size() > 0)
> + {
> + return {_M_dyn_exts + _S_dynamic_index[__begin],
> + _M_dyn_exts + _S_dynamic_index[__end]};
> + }
> +
> private:
> using _S_storage = __array_traits<_IndexType,
> _S_rank_dynamic>::_Type;
> [[no_unique_address]] _S_storage _M_dyn_exts{};
> @@ -160,6 +174,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> || _Extent <= numeric_limits<_IndexType>::max();
> }
>
> + namespace __mdspan
> + {
> + template<typename _Extents>
> + constexpr span<const size_t>
> + __static_extents(size_t __begin = 0, size_t __end =
> _Extents::rank())
> + noexcept
> + { return _Extents::_S_storage::_S_static_extents(__begin, __end); }
> +
> + template<typename _Extents>
> + constexpr span<const typename _Extents::index_type>
> + __dynamic_extents(const _Extents& __exts, size_t __begin = 0,
> + size_t __end = _Extents::rank()) noexcept
> + {
> + return __exts._M_exts._M_dynamic_extents(__begin, __end);
> + }
> + }
> +
> template<typename _IndexType, size_t... _Extents>
> class extents
> {
> @@ -251,7 +282,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> : _M_exts(span<const _OIndexType, _Nm>(__exts))
> { }
>
> -
> template<__mdspan::__valid_index_type<index_type> _OIndexType,
> size_t _Nm>
> requires (_Nm == rank() || _Nm == rank_dynamic())
> constexpr explicit(_Nm != rank_dynamic())
> @@ -276,6 +306,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> }
>
> private:
> + friend span<const size_t>
> + __mdspan::__static_extents<extents>(size_t, size_t);
> +
> + friend span<const index_type>
> + __mdspan::__dynamic_extents<extents>(const extents&, size_t,
> size_t);
> +
> using _S_storage = __mdspan::_ExtentsStorage<
> _IndexType, array<size_t, sizeof...(_Extents)>{_Extents...}>;
> [[no_unique_address]] _S_storage _M_exts;
> @@ -286,6 +322,72 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> namespace __mdspan
> {
> + template<typename _Tp, size_t _Nm>
> + constexpr bool
> + __contains_zero(span<_Tp, _Nm> __exts) noexcept
> + {
> + for (size_t __i = 0; __i < __exts.size(); ++__i)
> + if (__exts[__i] == 0)
> + return true;
> + return false;
> + }
> +
> + template<typename _Extents>
> + constexpr bool
> + __empty(const _Extents& __exts) noexcept
> + {
> + if constexpr (__contains_zero(__static_extents<_Extents>()))
> + return true;
> + else
> + {
>
I would preffer continuing if/else chain here:
+ if constexpr (__contains_zero(__static_extents<_Extents>()))
+ return true;
+ else if if constexpr (_Extents::rank_dynamic() > 0)
+ return __contains_zero(__dynamic_extents(__exts));
+ else
+ return false;
But changing it is not necessary, so if there are no major comments for
other
patches, we do not need to create new revision.
> + if constexpr (_Extents::rank_dynamic() > 0)
> + return __contains_zero(__dynamic_extents(__exts));
> + else
> + return false;
>
+ }
> + }
> +
> + constexpr size_t
> + __static_extents_prod(const auto& __sta_exts) noexcept
> + {
> + size_t __ret = 1;
> + for (auto __factor : __sta_exts)
> + if (__factor != dynamic_extent)
> + __ret *= __factor;
> + return __ret;
> + }
> +
> + template<typename _Extents>
> + constexpr typename _Extents::index_type
> + __exts_prod(const _Extents& __exts, size_t __begin, size_t __end)
> noexcept
> + {
> + using _IndexType = typename _Extents::index_type;
> +
> + size_t __ret = 1;
> + if constexpr (_Extents::rank_dynamic() != _Extents::rank())
> + {
> + auto __sta_exts = __static_extents<_Extents>(__begin, __end);
> + __ret = __static_extents_prod(__sta_exts);
> + if (__ret == 0)
> + return 0;
> + }
> +
> + if constexpr (_Extents::rank_dynamic() > 0)
> + for (auto __factor : __dynamic_extents(__exts, __begin, __end))
> + __ret *= size_t(__factor);
> + return _IndexType(__ret);
> + }
> +
> + template<typename _Extents>
> + constexpr typename _Extents::index_type
> + __fwd_prod(const _Extents& __exts, size_t __r) noexcept
> + { return __exts_prod(__exts, 0, __r); }
> +
> + template<typename _Extents>
> + constexpr typename _Extents::index_type
> + __rev_prod(const _Extents& __exts, size_t __r) noexcept
> + { return __exts_prod(__exts, __r + 1, __exts.rank()); }
> +
> template<typename _IndexType, size_t... _Counts>
> auto __build_dextents_type(integer_sequence<size_t, _Counts...>)
> -> extents<_IndexType, ((void) _Counts, dynamic_extent)...>;
> @@ -304,6 +406,208 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> explicit extents(_Integrals...) ->
> extents<size_t, __mdspan::__dynamic_extent<_Integrals>()...>;
>
> + struct layout_left
> + {
> + template<typename _Extents>
> + class mapping;
> + };
> +
> + namespace __mdspan
> + {
> + template<typename _Tp>
> + constexpr bool __is_extents = false;
> +
> + template<typename _IndexType, size_t... _Extents>
> + constexpr bool __is_extents<extents<_IndexType, _Extents...>> =
> true;
> +
> + template<typename _Extents, typename... _Indices>
> + constexpr typename _Extents::index_type
> + __linear_index_left(const _Extents& __exts, _Indices... __indices)
> + noexcept
> + {
> + using _IndexType = typename _Extents::index_type;
> + _IndexType __res = 0;
> + if constexpr (sizeof...(__indices) > 0)
> + {
> + _IndexType __mult = 1;
> + auto __update = [&, __pos = 0u](_IndexType __idx) mutable
> + {
> + __res += __idx * __mult;
> + __mult *= __exts.extent(__pos);
> + ++__pos;
> + };
> + (__update(__indices), ...);
> + }
> + return __res;
> + }
> +
> + template<typename _Extents,
> + typename _IndexType = typename _Extents::index_type>
> + consteval _IndexType
> + __static_quotient(_IndexType __nom =
> numeric_limits<_IndexType>::max())
> + {
> + auto __sta_exts = __static_extents<_Extents>();
> + for (auto __factor : __sta_exts)
> + {
> + if (__factor != dynamic_extent)
> + __nom /= _IndexType(__factor);
> + if (__nom == 0)
> + break;
> + }
> + return __nom;
> + }
> +
> + template<typename _Extents>
> + constexpr bool
> + __is_representable_extents(const _Extents& __exts) noexcept
> + {
> + using _IndexType = _Extents::index_type;
> +
> + if constexpr (__contains_zero(__static_extents<_Extents>()))
> + return true;
> + else
> + {
> + constexpr auto __sta_quo = __static_quotient<_Extents>();
> + if constexpr (_Extents::rank_dynamic() == 0)
> + return __sta_quo != 0;
> + else
> + {
> + auto __dyn_exts = __dynamic_extents(__exts);
> + if (__contains_zero(__dyn_exts))
> + return true;
> +
> + if constexpr (__sta_quo == 0)
> + return false;
> + else
> + {
> + auto __dyn_quo = _IndexType(__sta_quo);
> + for (auto __factor : __dyn_exts)
> + {
> + __dyn_quo /= __factor;
> + if (__dyn_quo == 0)
> + return false;
> + }
> + return true;
> + }
> + }
> + }
> + }
> +
> + template<typename _Extents, typename _IndexType>
> + concept __representable_size = _Extents::rank_dynamic() != 0
> + || __contains_zero(__static_extents<_Extents>())
> + || (__static_quotient<_Extents, _IndexType>() != 0);
> +
> + template<typename _Layout, typename _Mapping>
> + concept __mapping_of =
> + is_same_v<typename _Layout::mapping<typename
> _Mapping::extents_type>,
> + _Mapping>;
> +
> + template<typename _Mapping>
> + concept __standardized_mapping = __mapping_of<layout_left,
> _Mapping>;
> +
> + // A tag type to create internal ctors.
> + class __internal_ctor
> + { };
> + }
> +
> + template<typename _Extents>
> + class layout_left::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_left;
> +
> + 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{})
> + { }
> +
> + 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_left(_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::__fwd_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 ba468530338..8ea57132a2a 100644
> --- a/libstdc++-v3/src/c++23/std.cc.in
> +++ b/libstdc++-v3/src/c++23/std.cc.in
> @@ -1844,6 +1844,7 @@ export namespace std
> export namespace std
> {
> using std::extents;
> + using std::layout_left;
> // FIXME layout_*, default_accessor and mdspan
> }
> #endif
> --
> 2.49.0
>
>
