6.5 KiB
[mdspan.layout.leftpad.overview]
23 Containers library [containers]
23.7 Views [views]
23.7.3 Multidimensional access [views.multidim]
23.7.3.4 Layout mapping [mdspan.layout]
23.7.3.4.8 Class template layout_left_padded::mapping [mdspan.layout.leftpad]
23.7.3.4.8.1 Overview [mdspan.layout.leftpad.overview]
layout_left_padded provides a layout mapping that behaves like layout_left::mapping, except that the padding stride stride(1) can be greater than or equal to extent(0).
namespace std {template<size_t PaddingValue>templateclass layout_left_padded::mapping {public:static constexpr size_t padding_value = PaddingValue; 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_padded; private:static constexpr size_t rank_ = extents_type::rank(); // exposition onlystatic constexpr size_t first-static-extent = // exposition only extents_type::static_extent(0); // [mdspan.layout.leftpad.expo], exposition-only membersstatic constexpr size_t static-padding-stride = see below; // exposition onlypublic:// [mdspan.layout.leftpad.cons], constructorsconstexpr mapping() noexcept : mapping(extents_type{}) {}constexpr mapping(const mapping&) noexcept = default; constexpr mapping(const extents_type&); templateconstexpr mapping(const extents_type&, OtherIndexType); templateconstexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_left::mapping&); templateconstexpr explicit(extents_type::rank() > 0) mapping(const layout_stride::mapping&); templateconstexpr explicit(see below) mapping(const LayoutLeftPaddedMapping&); templateconstexpr explicit(see below) mapping(const LayoutRightPaddedMapping&) noexcept; constexpr mapping& operator=(const mapping&) noexcept = default; // [mdspan.layout.leftpad.obs], observersconstexpr const extents_type& extents() const noexcept { return extents_; }constexpr array<index_type, rank_> strides() const noexcept; constexpr index_type required_span_size() const noexcept; template<class... Indices>constexpr index_type operator()(Indices...) const noexcept; static constexpr bool is_always_unique() noexcept { return true; }static constexpr bool is_always_exhaustive() noexcept; static constexpr bool is_always_strided() noexcept { return true; }static constexpr bool is_unique() noexcept { return true; }constexpr bool is_exhaustive() const noexcept; static constexpr bool is_strided() noexcept { return true; }constexpr index_type stride(rank_type) const noexcept; templatefriend constexpr bool operator==(const mapping&, const LayoutLeftPaddedMapping&) noexcept; private:// [mdspan.layout.leftpad.expo], exposition-only members index_type stride-1 = static-padding-stride; // exposition only extents_type extents_{}; // exposition only// [mdspan.sub.map], submdspan mapping specializationtemplate<class... SliceSpecifiers>constexpr auto submdspan-mapping-impl(SliceSpecifiers...) const // exposition only-> see below; template<class... SliceSpecifiers>friend constexpr auto submdspan_mapping(const mapping& src, SliceSpecifiers... slices) {return src.submdspan-mapping-impl(slices...); }};}
If Extents is not a specialization of extents, then the program is ill-formed.
layout_left_padded::mapping is a trivially copyable type that models regular for each E.
Throughout [mdspan.layout.leftpad], let P_rank be the following size rank_ parameter pack of size_t values:
the empty parameter pack, if rank_ equals zero;
otherwise, 0zu, if rank_ equals one;
otherwise, the parameter pack 0zu, 1zu, …, rank_- 1.
Mandates:
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If rank_dynamic() == 0 is true, then the size of the multidimensional index space Extents() is representable as a value of type index_type.
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padding_value is representable as a value of type index_type.
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If
rank_ is greater than one,
padding_value does not equal dynamic_extent, and
first-static-extent does not equal dynamic_extent,
then LEAST-MULTIPLE-AT-LEAST(padding_value, first-static-extent) is representable as a value of type size_t, and is representable as a value of type index_type.
rank_ is greater than one,
padding_value does not equal dynamic_extent, and
extents_type::static_extent(k) does not equal dynamic_extent for all k in the range [0, extents_type::rank()),
then the product ofLEAST-MULTIPLE-AT-LEAST(padding_value, ext.static_extent(0)) and all values ext.static_extent(k) with k in the range of [1, rank_) is representable as a value of type size_t, and is representable as a value of type index_type.