tmp/tmpo8zqg290/{from.md → to.md}
RENAMED
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| 1 |
+
###### Overview <a id="mdspan.layout.leftpad.overview">[[mdspan.layout.leftpad.overview]]</a>
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+
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+
`layout_left_padded` provides a layout mapping that behaves like
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`layout_left::mapping`, except that the padding stride `stride(1)` can
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be greater than or equal to `extent(0)`.
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+
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``` cpp
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namespace std {
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+
template<size_t PaddingValue>
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+
template<class Extents>
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+
class layout_left_padded<PaddingValue>::mapping {
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public:
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static constexpr size_t padding_value = PaddingValue;
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+
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+
using extents_type = Extents;
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using index_type = extents_type::index_type;
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using size_type = extents_type::size_type;
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using rank_type = extents_type::rank_type;
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using layout_type = layout_left_padded<PaddingValue>;
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+
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private:
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static constexpr size_t rank_ = extents_type::rank(); // exposition only
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static constexpr size_t first-static-extent = // exposition only
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extents_type::static_extent(0);
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+
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// [mdspan.layout.leftpad.expo], exposition-only members
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static constexpr size_t static-padding-stride = see below; // exposition only
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public:
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// [mdspan.layout.leftpad.cons], constructors
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constexpr mapping() noexcept : mapping(extents_type{}) {}
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constexpr mapping(const mapping&) noexcept = default;
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constexpr mapping(const extents_type&);
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template<class OtherIndexType>
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constexpr mapping(const extents_type&, OtherIndexType);
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template<class OtherExtents>
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constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
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mapping(const layout_left::mapping<OtherExtents>&);
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template<class OtherExtents>
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constexpr explicit(extents_type::rank() > 0)
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mapping(const layout_stride::mapping<OtherExtents>&);
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template<class LayoutLeftPaddedMapping>
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constexpr explicit(see below)
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mapping(const LayoutLeftPaddedMapping&);
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template<class LayoutRightPaddedMapping>
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constexpr explicit(see below)
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mapping(const LayoutRightPaddedMapping&) noexcept;
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constexpr mapping& operator=(const mapping&) noexcept = default;
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// [mdspan.layout.leftpad.obs], observers
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constexpr const extents_type& extents() const noexcept { return extents_; }
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constexpr array<index_type, rank_> strides() const noexcept;
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constexpr index_type required_span_size() const noexcept;
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template<class... Indices>
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constexpr index_type operator()(Indices...) const noexcept;
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static constexpr bool is_always_unique() noexcept { return true; }
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static constexpr bool is_always_exhaustive() noexcept;
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static constexpr bool is_always_strided() noexcept { return true; }
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static constexpr bool is_unique() noexcept { return true; }
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constexpr bool is_exhaustive() const noexcept;
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static constexpr bool is_strided() noexcept { return true; }
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constexpr index_type stride(rank_type) const noexcept;
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template<class LayoutLeftPaddedMapping>
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friend constexpr bool operator==(const mapping&, const LayoutLeftPaddedMapping&) noexcept;
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private:
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// [mdspan.layout.leftpad.expo], exposition-only members
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index_type stride-1 = static-padding-stride; // exposition only
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| 75 |
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extents_type extents_{}; // exposition only
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// [mdspan.sub.map], submdspan mapping specialization
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template<class... SliceSpecifiers>
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constexpr auto submdspan-mapping-impl(SliceSpecifiers...) const // exposition only
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-> see below;
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template<class... SliceSpecifiers>
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friend constexpr auto submdspan_mapping(const mapping& src, SliceSpecifiers... slices) {
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return src.submdspan-mapping-impl(slices...);
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| 84 |
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}
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| 85 |
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};
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| 86 |
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}
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| 87 |
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```
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If `Extents` is not a specialization of `extents`, then the program is
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ill-formed.
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`layout_left_padded::mapping<E>` is a trivially copyable type that
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models `regular` for each `E`.
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Throughout [[mdspan.layout.leftpad]], let `P_rank` be the following size
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*`rank_`* parameter pack of `size_`t values:
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- the empty parameter pack, if *`rank_`* equals zero;
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- otherwise, `0zu`, if *`rank_`* equals one;
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- otherwise, the parameter pack `0zu`, `1zu`, …, `rank_- 1`.
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*Mandates:*
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- If `rank_dynamic() == 0` is `true`, then the size of the
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| 105 |
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multidimensional index space `Extents()` is representable as a value
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| 106 |
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of type `index_type`.
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- `padding_value` is representable as a value of type `index_type`.
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| 108 |
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- If
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| 109 |
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- *`rank_`* is greater than one,
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| 110 |
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- `padding_value` does not equal `dynamic_extent`, and
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| 111 |
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- *`first-static-extent`* does not equal `dynamic_extent`,
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| 112 |
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| 113 |
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then `LEAST-MULTIPLE-AT-LEAST(padding_value, first-static-extent)` is
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| 114 |
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representable as a value of type `size_t`, and is representable as a
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| 115 |
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value of type `index_type`.
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| 116 |
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- If
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| 117 |
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- *`rank_`* is greater than one,
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| 118 |
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- `padding_value` does not equal `dynamic_extent`, and
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| 119 |
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- `extents_type::static_extent(k)` does not equal `dynamic_extent` for
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| 120 |
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all k in the range \[`0`, `extents_type::rank()`),
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| 121 |
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then the product of
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| 123 |
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`LEAST-MULTIPLE-AT-LEAST(padding_value, ext.static_extent(0))` and all
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| 124 |
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values `ext.static_extent(k)` with k in the range of \[`1`, *`rank_`*)
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| 125 |
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is representable as a value of type `size_t`, and is representable as
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| 126 |
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a value of type `index_type`.
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| 127 |
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