[mdspan.layout.leftpad.cons] (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]

23.7.3.4.8.3 Constructors [mdspan.layout.leftpad.cons]

constexpr mapping(const extents_type& ext);

Preconditions:

• The size of the multidimensional index space ext is representable as a value of type index_type.
• If rank_ is greater than one andpadding_value does not equal dynamic_extent, then LEAST-MULTIPLE-AT-LEAST(padding_value, ext.extent(0))is representable as a value of type index_type.
• If rank_ is greater than one andpadding_value does not equal dynamic_extent, then the product of_LEAST-MULTIPLE-AT-LEAST_(padding_value, ext.extent(0)) and all values ext.extent(k)with k in the range of [1, _rank__) is representable as a value of type index_type.

Effects:

• Direct-non-list-initializes extents_ with ext; and
• if rank_ is greater than one, direct-non-list-initializes stride-1
  • with ext.extent(0) if padding_value is dynamic_extent,
  • otherwise with_LEAST-MULTIPLE-AT-LEAST_(padding_value, ext.extent(0)).

template<class OtherIndexType> constexpr mapping(const extents_type& ext, OtherIndexType pad);

Constraints:

• is_convertible_v<OtherIndexType, index_type> is true.
• is_nothrow_constructible_v<index_type, OtherIndexType> is true.

Preconditions:

• pad is representable as a value of type index_type.
• extents_type​::​index-cast(pad) is greater than zero.
• If rank_ is greater than one, then LEAST-MULTIPLE-AT-LEAST(pad, ext.extent(0))is representable as a value of type index_type.
• If rank_ is greater than one, then the product of_LEAST-MULTIPLE-AT-LEAST_(pad, ext.extent(0)) and all values ext.extent(k)with k in the range of [1, _rank__) is representable as a value of type index_type.
• If padding_value is not equal to dynamic_extent,padding_value equals extents_type​::​index-cast(pad).

Effects: Direct-non-list-initializes extents_ with ext, and if rank_ is greater than one, direct-non-list-initializes stride-1 with_LEAST-MULTIPLE-AT-LEAST_(pad, ext.extent(0)).

template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_left::mapping<OtherExtents>& other);

Constraints: is_constructible_v<extents_type, OtherExtents> is true.

Mandates: If OtherExtents​::​rank() is greater than 1, then(static-padding-stride == dynamic_extent) || (OtherExtents::static_extent(0) == dynamic_extent) || (static-padding-stride == OtherExtents::static_extent(0)) is true.

Preconditions:

• If extents_type​::​rank() > 1 is true andpadding_value == dynamic_extent is false, then other.stride(1) equals_LEAST-MULTIPLE-AT-LEAST_(padding_value, extents_type::index-cast(other.extents().extent(0))) and
• other.required_span_size() is representable as a value of type index_type.

Effects: Equivalent to mapping(other.extents()).

template<class OtherExtents> constexpr explicit(rank_ > 0) mapping(const layout_stride::mapping<OtherExtents>& other);

Constraints: is_constructible_v<extents_type, OtherExtents> is true.

Preconditions:

• If rank_ is greater than 1 andpadding_value does not equal dynamic_extent, then other.stride(1) equals_LEAST-MULTIPLE-AT-LEAST_(padding_value, extents_type::index-cast(other.extents().extent(0)))
• If rank_ is greater than 0, then other.stride(0) equals 1.
• If rank_ is greater than 2, then for all r in the range [2, rank_),other.stride(r) equals(other.extents().fwd-prod-of-extents(r) / other.extents().extent(0)) * other.stride(1)
• other.required_span_size() is representable as a value of type index_type.

Effects:

• Direct-non-list-initializes extents_ with other.extents() and
• if rank_ is greater than one, direct-non-list-initializes stride-1 withother.stride(1).

template<class LayoutLeftPaddedMapping> constexpr explicit(_see below_) mapping(const LayoutLeftPaddedMapping& other);

Constraints:

• is-layout-left-padded-mapping-of<LayoutLeftPaddedMapping>is true.
• is_constructible_v<extents_type, typename LayoutLeftPaddedMapping​::​extents_type>
  is true.

Mandates: If rank_ is greater than 1, thenpadding_value == dynamic_extent ||LayoutLeftPaddedMapping::padding_value == dynamic_extent ||padding_value == LayoutLeftPaddedMapping::padding_valueis true.

• If rank_ is greater than 1 andpadding_value does not equal dynamic_extent, then other.stride(1) equals_LEAST-MULTIPLE-AT-LEAST_(padding_value, extents_type::index-cast(other.extent(0)))
• other.required_span_size() is representable as a value of type index_type.

Effects:

• Direct-non-list-initializes extents_ with other.extents() and
• if rank_ is greater than one, direct-non-list-initializes stride-1 with other.stride(1).

Remarks: The expression inside explicit is equivalent to:rank_> 1 && (padding_value != dynamic_extent || LayoutLeftPaddedMapping::padding_value == dynamic_extent)

template<class LayoutRightPaddedMapping> constexpr explicit(_see below_) mapping(const LayoutRightPaddedMapping& other) noexcept;

Constraints:

• is-layout-right-padded-mapping-of<LayoutRightPaddedMapping>is true or
  is-mapping-of<layout_right, LayoutRightPaddedMapping>is true.
• rank_ equals zero or one.
• is_constructible_v<extents_type, typename LayoutRightPaddedMapping​::​extents_-
  type>is true.

Preconditions: other.required_span_size() is representable as a value of type index_type.

Effects: Direct-non-list-initializes extents_ with other.extents().

Remarks: The expression inside explicit is equivalent to:!is_convertible_v<typename LayoutRightPaddedMapping::extents_type, extents_type>

[Note 1:

Neither the input mapping nor the mapping to be constructed uses the padding stride in the rank-0 or rank-1 case, so the padding stride does not affect either the constraints or the preconditions.

— _end note_]