On Fri, May 30, 2025 at 6:47 PM Luc Grosheintz <luc.groshei...@gmail.com> wrote:
> Implements the remaining parts of layout_left and layout_right; and all > of layout_stride. > > The implementation of layout_stride::mapping::is_exhaustive applies > the following change to the standard: > > 4266. layout_stride::mapping should treat empty mappings as exhaustive > > https://cplusplus.github.io/LWG/issue4266 > > The preconditions for layout_stride(extents, strides) are not checked. > > libstdc++-v3/ChangeLog: > > * include/std/mdspan (layout_stride): New class. > * src/c++23/std.cc.in: Add layout_stride. > > Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com> > --- > LGTM. Only two comments for formatting and unused variable. > libstdc++-v3/include/std/mdspan | 245 ++++++++++++++++++++++++++++++- > libstdc++-v3/src/c++23/std.cc.in | 3 +- > 2 files changed, 246 insertions(+), 2 deletions(-) > > diff --git a/libstdc++-v3/include/std/mdspan > b/libstdc++-v3/include/std/mdspan > index 8e406731568..1250adefc14 100644 > --- a/libstdc++-v3/include/std/mdspan > +++ b/libstdc++-v3/include/std/mdspan > @@ -418,6 +418,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > class mapping; > }; > > + struct layout_stride > + { > + template<typename _Extents> > + class mapping; > + }; > + > namespace __mdspan > { > template<typename _Tp> > @@ -511,7 +517,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > template<typename _Mapping> > concept __standardized_mapping = __mapping_of<layout_left, _Mapping> > - || __mapping_of<layout_right, > _Mapping>; > + || __mapping_of<layout_right, > _Mapping> > + || __mapping_of<layout_stride, > _Mapping>; > > // A tag type to create internal ctors. > class __internal_ctor > @@ -557,6 +564,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > : mapping(__other.extents(), __mdspan::__internal_ctor{}) > { } > > + template<typename _OExtents> > + requires is_constructible_v<extents_type, _OExtents> > + constexpr explicit(extents_type::rank() > 0) > + mapping(const layout_stride::mapping<_OExtents>& __other) > + : mapping(__other.extents(), __mdspan::__internal_ctor{}) > + { __glibcxx_assert(*this == __other); } > + > constexpr mapping& > operator=(const mapping&) noexcept = default; > > @@ -687,6 +701,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > : mapping(__other.extents(), __mdspan::__internal_ctor{}) > { } > > + template<class _OExtents> > + requires is_constructible_v<extents_type, _OExtents> > + constexpr explicit(extents_type::rank() > 0) > + mapping(const layout_stride::mapping<_OExtents>& __other) noexcept > + : mapping(__other.extents(), __mdspan::__internal_ctor{}) > + { __glibcxx_assert(*this == __other); } > + > constexpr mapping& > operator=(const mapping&) noexcept = default; > > @@ -759,6 +780,228 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > [[no_unique_address]] extents_type _M_extents{}; > }; > > + namespace __mdspan > + { > + template<typename M> > + concept __mapping_alike = requires > + { > + requires __is_extents<typename M::extents_type>; > + { M::is_always_strided() } -> same_as<bool>; > + { M::is_always_exhaustive() } -> same_as<bool>; > + { M::is_always_unique() } -> same_as<bool>; > + bool_constant<M::is_always_strided()>::value; > + bool_constant<M::is_always_exhaustive()>::value; > + bool_constant<M::is_always_unique()>::value; > + }; > + > + template<typename _Mapping> > + constexpr typename _Mapping::index_type > + __offset(const _Mapping& __m) noexcept > + { > + using _IndexType = typename _Mapping::index_type; > + constexpr auto __rank = _Mapping::extents_type::rank(); > + > + if constexpr (__standardized_mapping<_Mapping>) > + return 0; > + else I would write this as else if (__empty(__m.extents()) return 0; else { /// .... } > + { > + if (__empty(__m.extents())) > + return 0; > + > + auto __impl = [&__m]<size_t... > _Counts>(index_sequence<_Counts...>) > + { return __m(((void) _Counts, _IndexType(0))...); }; > + return __impl(make_index_sequence<__rank>()); > + } > + } > + > + template<typename _Mapping, typename... _Indices> > + constexpr typename _Mapping::index_type > + __linear_index_strides(const _Mapping& __m, _Indices... __indices) > + noexcept > + { > + using _IndexType = typename _Mapping::index_type; > + _IndexType __res = 0; > + if constexpr (sizeof...(__indices) > 0) > + { > + auto __update = [&, __pos = 0u](_IndexType __idx) mutable > + { > + __res += __idx * __m.stride(__pos++); > + }; > + (__update(__indices), ...); > + } > + return __res; > + } > + } > + > + template<typename _Extents> > + class layout_stride::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_stride; > + > + static_assert(__mdspan::__representable_size<extents_type, > index_type>, > + "The size of extents_type must be representable as index_type"); > + > + constexpr > + mapping() noexcept > + { > + // The precondition is either statically asserted, or automatically > + // satisfied because dynamic extents are zero-initialzied. > + size_t __stride = 1; > + for (size_t __i = extents_type::rank(); __i > 0; --__i) > + { > + _M_strides[__i - 1] = index_type(__stride); > + __stride *= size_t(_M_extents.extent(__i - 1)); > + } > + } > + > + constexpr > + mapping(const mapping&) noexcept = default; > + > + template<__mdspan::__valid_index_type<index_type> _OIndexType> > + constexpr > + mapping(const extents_type& __exts, > + span<_OIndexType, extents_type::rank()> __strides) noexcept > + : _M_extents(__exts) > + { > + for (size_t __i = 0; __i < extents_type::rank(); ++__i) > + _M_strides[__i] = index_type(as_const(__strides[__i])); > + } > + > + template<__mdspan::__valid_index_type<index_type> _OIndexType> > + constexpr > + mapping(const extents_type& __exts, > + const array<_OIndexType, extents_type::rank()>& __strides) > + noexcept > + : mapping(__exts, > + span<const _OIndexType, extents_type::rank()>(__strides)) > + { } > + > + template<__mdspan::__mapping_alike _StridedMapping> > + requires (is_constructible_v<extents_type, > + typename > _StridedMapping::extents_type> > + && _StridedMapping::is_always_unique() > + && _StridedMapping::is_always_strided()) > + constexpr explicit(!( > + is_convertible_v<typename _StridedMapping::extents_type, > extents_type> > + && __mdspan::__standardized_mapping<_StridedMapping>)) > + mapping(const _StridedMapping& __other) noexcept > + : _M_extents(__other.extents()) > + { > + __glibcxx_assert(__mdspan::__offset(__other) == 0); > + if constexpr (cmp_greater( > + numeric_limits<typename > _StridedMapping::index_type>::max(), > + numeric_limits<index_type>::max())) > + __glibcxx_assert(!cmp_less(numeric_limits<index_type>::max(), > + __other.required_span_size()) > + && "other.required_span_size() must be representable" > + " as index_type"); > + if constexpr (extents_type::rank() > 0) > + for (size_t __i = 0; __i < extents_type::rank(); ++__i) > + _M_strides[__i] = index_type(__other.stride(__i)); > + } > + > + constexpr mapping& > + operator=(const mapping&) noexcept = default; > + > + constexpr const extents_type& > + extents() const noexcept { return _M_extents; } > + > + constexpr array<index_type, extents_type::rank()> > + strides() const noexcept > + { > + array<index_type, extents_type::rank()> __ret; > + for (size_t __i = 0; __i < extents_type::rank(); ++__i) > + __ret[__i] = _M_strides[__i]; > + return __ret; > + } > + > + constexpr index_type > + required_span_size() const noexcept > + { > + if (__mdspan::__empty(_M_extents)) > + return 0; > + > + index_type __ret = 1; > + for (size_t __i = 0; __i < extents_type::rank(); ++__i) > + __ret += (_M_extents.extent(__i) - 1) * _M_strides[__i]; > + return __ret; > + } > + > + 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_strides(*this, > + static_cast<index_type>(__indices)...); > + } > + > + static constexpr bool > + is_always_unique() noexcept { return true; } > + > + // _GLIBCXX_RESOLVE_LIB_DEFECTS > + // 4266. layout_stride::mapping should treat empty mappings as > exhaustive > + static constexpr bool > + is_always_exhaustive() noexcept > + { > + return (_Extents::rank() == 0) || __mdspan::__contains_zero( > + __mdspan::__static_extents<extents_type>()); > + } > + > + static constexpr bool > + is_always_strided() noexcept { return true; } > + > + static constexpr bool > + is_unique() noexcept { return true; } > + > + // _GLIBCXX_RESOLVE_LIB_DEFECTS > + // 4266. layout_stride::mapping should treat empty mappings as > exhaustive > + constexpr bool > + is_exhaustive() const noexcept > + { > + if constexpr (!is_always_exhaustive()) > + { > + constexpr auto __rank = extents_type::rank(); > The rank variable is unused now. > + auto __size = __mdspan::__fwd_prod(_M_extents, __rank); > + if(__size > 0) > + return __size == required_span_size(); > + } > + return true; > + } > + > + static constexpr bool > + is_strided() noexcept { return true; } > + > + constexpr index_type > + stride(rank_type __r) const noexcept { return _M_strides[__r]; } > + > + template<__mdspan::__mapping_alike _OMapping> > + requires ((extents_type::rank() == _OMapping::extents_type::rank()) > + && _OMapping::is_always_strided()) > + friend constexpr bool > + operator==(const mapping& __self, const _OMapping& __other) > noexcept > + { > + if (__self.extents() != __other.extents()) > + return false; > + if constexpr (extents_type::rank() > 0) > + for (size_t __i = 0; __i < extents_type::rank(); ++__i) > + if (!cmp_equal(__self.stride(__i), __other.stride(__i))) > + return false; > + return __mdspan::__offset(__other) == 0; > + } > + > + private: > + using _S_strides_t = typename __array_traits<index_type, > + > extents_type::rank()>::_Type; > + [[no_unique_address]] extents_type _M_extents; > + [[no_unique_address]] _S_strides_t _M_strides; > + }; > + > _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 fe1407d71da..9a52a7e7728 100644 > --- a/libstdc++-v3/src/c++23/std.cc.in > +++ b/libstdc++-v3/src/c++23/std.cc.in > @@ -1846,7 +1846,8 @@ export namespace std > using std::extents; > using std::layout_left; > using std::layout_right; > - // FIXME layout_*, default_accessor and mdspan > + using std::layout_stride; > + // FIXME layout_left_padded, layout_right_padded, default_accessor and > mdspan > } > #endif > > -- > 2.49.0 > >
