[mdspan.layout.leftpad.overview] (original) (raw)

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> template<class Extents> class layout_left_padded<PaddingValue>::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<PaddingValue>;private: static constexpr size_t rank_ = extents_type::rank(); static constexpr size_t first-static-extent = extents_type::static_extent(0);static constexpr size_t static-padding-stride = see below; public: constexpr mapping() noexcept : mapping(extents_type{}) {} constexpr mapping(const mapping&) noexcept = default;constexpr mapping(const extents_type&);template<class OtherIndexType> constexpr mapping(const extents_type&, OtherIndexType);template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_left::mapping<OtherExtents>&);template<class OtherExtents> constexpr explicit(extents_type::rank() > 0) mapping(const layout_stride::mapping<OtherExtents>&);template<class LayoutLeftPaddedMapping> constexpr explicit(see below) mapping(const LayoutLeftPaddedMapping&);template<class LayoutRightPaddedMapping> constexpr explicit(see below) mapping(const LayoutRightPaddedMapping&) noexcept;constexpr mapping& operator=(const mapping&) noexcept = default;constexpr 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;template<class LayoutLeftPaddedMapping> friend constexpr bool operator==(const mapping&, const LayoutLeftPaddedMapping&) noexcept;private: index_type stride-1 = static-padding-stride; extents_type extents_{}; template<class... SliceSpecifiers> constexpr auto submdspan-mapping-impl(SliceSpecifiers...) const -> 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<E> 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:

• If rank_dynamic() == 0 is true, then the size of the multidimensional index space Extents()is representable as a value of type index_type.
• padding_value is representable as a value of type index_type.
• 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.
• If
  • rank_ is greater than one,
  • padding_value does not equal dynamic_extent, and
  • extents_type​::​static_extent(k) does not equal dynamic_extentfor all k in the range [0, extents_type​::​rank()),
    then the product of_LEAST-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.