cppdraft_translate/cppdraft/mdspan/sub/extents.md

[mdspan.sub.extents]

23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.7 submdspan [mdspan.sub]

23.7.3.7.5 submdspan_extents function [mdspan.sub.extents]

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template<class IndexType, size_t... Extents, class... SliceSpecifiers> constexpr auto submdspan_extents(const extents<IndexType, Extents...>& src, SliceSpecifiers... slices);

1

#

Constraints: sizeof...(slices) equals sizeof...(Extents).

2

#

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

• (2.1)

Sk models convertible_to,

• (2.2)

Sk models index-pair-like,

• (2.3)

is_convertible_v<Sk, full_extent_t> is true, or

• (2.4)

Sk is a specialization of strided_slice.

3

#

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

• (3.1)

if Sk is a specialization of strided_slice

• (3.1.1)

sk.extent=0, or

• (3.1.2)

sk.stride>0

• (3.2)

0 ≤ first_<IndexType, k>(slices...) ≤ last_(src, slices...) ≤ src.extent(k)

4

#

Let SubExtents be a specialization of extents such that:

• (4.1)

SubExtents​::​rank() equals the number of k such thatSk does not model convertible_to; and

• (4.2)

for each rank index k of Extents such thatmap-rank[k] != dynamic_extent is true,SubExtents​::​static_extent(map-rank[k]) equals:

• (4.2.1)

Extents​::​static_extent(k) if is_convertible_v<Sk, full_extent_t> is true; otherwise

• (4.2.2)

de-ice(tuple_element_t<1, Sk>()) -de-ice(tuple_element_t<0, Sk>()) if Sk models index-pair-like, and both tuple_element_t<0, Sk> and tuple_element_t<1, Sk> model integral-constant-like; otherwise

• (4.2.3)

0, if Sk is a specialization of strided_slice, whose extent_type models integral-constant-like, for which extent_type() equals zero; otherwise

• (4.2.4)

1 + (de-ice(Sk​::​extent_type()) - 1) /de-ice(Sk​::​stride_type()), if Sk is a specialization of strided_slice whose extent_type and stride_type model integral-constant-like;

• (4.2.5)

otherwise, dynamic_extent.

5

#

Returns: A value ext of type SubExtents such that for each k for which map-rank[k] != dynamic_extent is true,ext.extent(map-rank[k]) equals:

• (5.1)

sk.extent == 0 ? 0 : 1 + (de-ice(sk.extent) - 1) / de-ice(sk.stride) if Sk is a specialization of strided_slice,

• (5.2)

otherwise,last_(src, slices...) - first_<IndexType, k>(slices...).