24 Containers library [containers]

24.7 Views [views]

24.7.3 Multidimensional access [views.multidim]

24.7.3.7 submdspan [mdspan.submdspan]

24.7.3.7.5 submdspan_extents function [mdspan.submdspan.extents]

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

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

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

(2.1)
$S_{k}$ models convertible_to<IndexType>,
(2.2)
$S_{k}$ models index-pair-like<IndexType>,
(2.3)
is_convertible_v< $S_{k}$ , full_extent_t> is true, or
(2.4)
$S_{k}$ is a specialization of strided_slice.

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

(3.1)
if $S_{k}$ is a specialization of strided_slice
- (3.1.1)
  $s_{k} .extent = 0$ , or
- (3.1.2)
  $s_{k} .stride > 0$
(3.2)
0 ≤ first_<IndexType, k>(slices...) ≤ last_<k>(src, slices...) ≤ src.extent(k)

Let SubExtents be a specialization of extents such that:

(4.1)
SubExtents::rank() equals the number of k such that $S_{k}$ does not model convertible_to<IndexType>; and
(4.2)
for each rank index k of Extents such that map-rank[k] != dynamic_extent is true, SubExtents::static_extent(map-rank[k]) equals:
- (4.2.1)
  Extents::static_extent(k) if is_convertible_v< $S_{k}$ , full_extent_t> is true; otherwise
- (4.2.2)
  de-ice(tuple_element_t<1, $S_{k}$ >()) - de-ice(tuple_element_t<0, $S_{k}$ >()) if $S_{k}$ models index-pair-like<IndexType>, and both tuple_element_t<0, $S_{k}$ > and tuple_element_t<1, $S_{k}$ > model integral-constant-like; otherwise
- (4.2.3)
  0, if $S_{k}$ 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( $S_{k}$ ::extent_type()) - 1) / de-ice( $S_{k}$ ::stride_type()), if $S_{k}$ is a specialization of strided_slice whose extent_type and stride_type model integral-constant-like;
- (4.2.5)
  otherwise, dynamic_extent.

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)
$s_{k}$ .extent == 0 ? 0 : 1 + (de-ice( $s_{k}$ .extent) - 1) / de-ice( $s_{k}$ .stride) if $S_{k}$ is a specialization of strided_slice,
(5.2)
otherwise, last_<k>(src, slices...) - first_<IndexType, k>(slices...).