cppdraft_translate/cppdraft/mdspan/sub/map.md

[mdspan.sub.map]

23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.7 submdspan [mdspan.sub]

23.7.3.7.6 Specializations of submdspan_mapping [mdspan.sub.map]

23.7.3.7.6.1 Common [mdspan.sub.map.common]

1

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The following elements apply to all functions in [mdspan.sub.map].

2

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Constraints: sizeof...(slices) equals extents_type​::​rank().

3

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Mandates: For each rank index k of extents(), exactly one of the following is true:

• (3.1)

Sk models convertible_to<index_type>,

• (3.2)

Sk models index-pair-like<index_type>,

• (3.3)

is_convertible_v<Sk, full_extent_t> is true, or

• (3.4)

Sk is a specialization of strided_slice.

4

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Preconditions: For each rank index k of extents(), all of the following are true:

• (4.1)

if Sk is a specialization of strided_slice,sk.extent is equal to zero orsk.stride is greater than zero; and

• (4.2)

0 ≤ first_<index_type, k>(slices...)
0 ≤ last_(extents(), slices...)
0 ≤ extents().extent(k)

5

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Let sub_ext be the result of submdspan_extents(extents(), slices...) and let SubExtents be decltype(sub_ext).

6

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Let sub_strides be an array<SubExtents​::​index_type, SubExtents​::​rank()> such that for each rank index k of extents() for which map-rank[k] is not dynamic_extent,sub_strides[map-rank[k]] equals:

• (6.1)

stride(k) * de-ice(sk.stride) if Sk is a specialization of strided_slice andsk.stride < sk.extent is true;

• (6.2)

otherwise, stride(k).

7

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Let P be a parameter pack such that is_same_v<make_index_sequence<rank()>, index_sequence<P...>> is true.

8

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If first_<index_type, k>(slices...) equals extents().extent(k) for any rank index k of extents(), then let offset be a value of type size_t equal to(*this).required_span_size().

Otherwise, let offset be a value of type size_t equal to(*this)(first_<index_type, P>(slices...)...).

9

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Given a layout mapping type M, a type S is aunit-stride slice for M if

• (9.1)

S is a specialization of strided_slice where S​::​stride_type models integral-constant-like and S​::​stride_type​::​value equals 1,

• (9.2)

S models index-pair-like<M​::​index_type>, or

• (9.3)

is_convertible_v<S, full_extent_t> is true.

23.7.3.7.6.2 layout_left specialization of submdspan_mapping [mdspan.sub.map.left]

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template<class Extents> template<class... SliceSpecifiers> constexpr auto layout_left::mapping<Extents>::submdspan-mapping-impl( SliceSpecifiers... slices) const -> see below;

1

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Returns:

• (1.1)

submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;

• (1.2)

otherwise,submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if SubExtents​::​rank() == 0 is true;

• (1.3)

otherwise,submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if

• (1.3.1)

for each k in the range [0, SubExtents​::​rank() - 1)), is_convertible_v<Sk, full_extent_t> is true; and

• (1.3.2)

for k equal to SubExtents​::​rank() - 1, Sk is a unit-stride slice for mapping;

[Note 1: If the above conditions are true, all Sk with k larger than SubExtents​::​rank() - 1 are convertible to index_type. — end note]

• (1.4)

otherwise,submdspan_mapping_result{layout_left_padded<S_static>::mapping(sub_ext, stride(u + 1)), offset} if for a value u for which u+1 is the smallest value p larger than zero for which Sp is a unit-stride slice for mapping, the following conditions are met:

• (1.4.1)

S0 is a unit-stride slice for mapping; and

• (1.4.2)

for each k in the range [u + 1, u + SubExtents​::​rank() - 1),is_convertible_v<Sk, full_extent_t> is true; and

• (1.4.3)

for k equal to u + SubExtents​::​rank() - 1,Sk is a unit-stride slice for mapping;

and where S_static is:

• (1.4.4)

dynamic_extent, if static_extent(k) is dynamic_extent for any k in the range [0, u + 1),

• (1.4.5)

otherwise, the product of all valuesstatic_extent(k) for k in the range [0, u + 1);

• (1.5)

otherwise,submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}

23.7.3.7.6.3 layout_right specialization of submdspan_mapping [mdspan.sub.map.right]

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template<class Extents> template<class... SliceSpecifiers> constexpr auto layout_right::mapping<Extents>::submdspan-mapping-impl( SliceSpecifiers... slices) const -> see below;

1

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Returns:

• (1.1)

submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;

• (1.2)

otherwise,submdspan_mapping_result{layout_right​::​mapping(sub_ext), offset}, if SubExtents​::​rank() == 0 is true;

• (1.3)

otherwise,submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if

• (1.3.1)

for each k in the range [rank_ - SubExtents​::​rank() + 1, rank_), is_convertible_v<Sk, full_extent_t> is true; and

• (1.3.2)

for k equal to _rank - SubExtents​::​rank(), Sk is a unit-stride slice for mapping;

[Note 1: If the above conditions are true, all Sk with k<_rank - SubExtents::rank() are convertible to index_type. — end note]

• (1.4)

otherwise,submdspan_mapping_result{layout_right_padded<S_static>::mapping(sub_ext, stride(rank_ - u - 2)), offset} if for a value u for which rank_−u−2 is the largest value p smaller than rank_ - 1 for which Sp is a unit-stride slice for mapping, the following conditions are met:

• (1.4.1)

for k equal to rank_ - 1,Sk is a unit-stride slice for mapping; and

• (1.4.2)

for each k in the range [rank_ - SubExtents​::​rank() - u + 1, rank_ - u - 1),is_convertible_v<Sk, full_extent_t> is true; and

• (1.4.3)

for k equal to rank_ - SubExtents​::​rank() - u,
Sk is a unit-stride slice for mapping;

and where S_static is:

• (1.4.4)

dynamic_extent, if static_extent(k) is dynamic_extent for any k in the range [rank_ - u - 1, rank_),

• (1.4.5)

otherwise, the product of all valuesstatic_extent(k) for k in the range [rank_ - u - 1, rank_);

• (1.5)

otherwise,submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}

23.7.3.7.6.4 layout_stride specialization of submdspan_mapping [mdspan.sub.map.stride]

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template<class Extents> template<class... SliceSpecifiers> constexpr auto layout_stride::mapping<Extents>::submdspan-mapping-impl( SliceSpecifiers... slices) const -> see below;

1

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Returns:

• (1.1)

submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;

• (1.2)

otherwise,submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}

23.7.3.7.6.5 layout_left_padded specialization of submdspan_mapping [mdspan.sub.map.leftpad]

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template<class Extents> template<class... SliceSpecifiers> constexpr auto layout_left_padded::mapping<Extents>::submdspan-mapping-impl( SliceSpecifiers... slices) const -> see below;

1

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Returns:

• (1.1)

submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;

• (1.2)

otherwise,submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if rank_ == 1 is true orSubExtents​::​rank() == 0 is true;

• (1.3)

otherwise,submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if

• (1.3.1)

SubExtents​::​rank() == 1 is true and

• (1.3.2)

S0 is a unit-stride slice for mapping;

• (1.4)

otherwise,submdspan_mapping_result{layout_left_padded<S_static>::mapping(sub_ext, stride(u + 1)), offset} if for a value u for which u + 1 is the smallest value p larger than zero for which Sp is a unit-stride slice for mapping, the following conditions are met:

• (1.4.1)

S0 is a unit-stride slice for mapping; and

• (1.4.2)

for each k in the range [u + 1, u + SubExtents​::​rank() - 1),is_convertible_v<Sk, full_extent_t> is true; and

• (1.4.3)

for k equal to u + SubExtents​::​rank() - 1,Sk is a unit-stride slice for mapping;

where S_static is:

• (1.4.4)

dynamic_extent, if static-padding-stride is dynamic_extent orstatic_extent(k) is dynamic_extent for any k in the range [1, u + 1),

• (1.4.5)

otherwise, the product of static-padding-stride and all values static_extent(k) for k in the range [1, u + 1);

• (1.5)

otherwise,submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}

23.7.3.7.6.6 layout_right_padded specialization of submdspan_mapping [mdspan.sub.map.rightpad]

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template<class Extents> template<class... SliceSpecifiers> constexpr auto layout_right_padded::mapping<Extents>::submdspan-mapping-impl( SliceSpecifiers... slices) const -> see below;

1

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Returns:

• (1.1)

submdspan_mapping_result{*this, 0}, if rank_ == 0 is true;

• (1.2)

otherwise,submdspan_mapping_result{layout_right​::​mapping(sub_ext), offset},
if rank_ == 1 is true orSubExtents​::​rank() == 0 is true;

• (1.3)

otherwise,submdspan_mapping_result{layout_right​::​mapping(sub_ext), offset}, if

• (1.3.1)

SubExtents​::​rank() == 1 is true and

• (1.3.2)

for k equal to rank_ - 1,Sk is a unit-stride slice for mapping;

• (1.4)

otherwise,submdspan_mapping_result{layout_right_padded<S_static>::mapping(sub_ext, stride(rank_ - u - 2)), offset} if for a value u for which rank_ - u - 2 is the largest value p smaller than rank_ - 1 for which Sp is a unit-stride slice for mapping, the following conditions are met:

• (1.4.1)

for k equal to rank_ - 1,Sk is a unit-stride slice for mapping; and

• (1.4.2)

for each k in the range [rank_ - SubExtents​::​rank() - u + 1, rank_ - u - 1)),is_convertible_v<Sk, full_extent_t> is true; and

• (1.4.3)

for k equal to rank_ - SubExtents​::​rank() - u,
Sk is a unit-stride slice for mapping;

and where S_static is:

• (1.4.4)

dynamic_extent if static-padding-stride is dynamic_extent or for any k in the range [rank_ - u - 1, rank_ - 1)static_extent(k) is dynamic_extent,

• (1.4.5)

otherwise, the product of static-padding-stride and all values static_extent(k) with k in the range [rank_ - u - 1, rank_ - 1);

• (1.5)

otherwise,submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}