24 Containers library [containers]

24.7 Views [views]

24.7.3 Multidimensional access [views.multidim]

24.7.3.7 submdspan [mdspan.submdspan]

24.7.3.7.6 Layout specializations of submdspan_mapping [mdspan.submdspan.mapping]

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

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

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

Let index_type be typename Extents::index_type.

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

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

(3.1)
$S_{k}$ models convertible_to<index_type>,
(3.2)
$S_{k}$ models index-pair-like<index_type>,
(3.3)
is_convertible_v< $S_{k}$ , full_extent_t> is true, or
(3.4)
$S_{k}$ is a specialization of strided_slice.

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

(4.1)
if $S_{k}$ is a specialization of strided_slice
- (4.1.1)
  $s_{k} .extent = 0$ , or
- (4.1.2)
  $s_{k} .stride > 0$
(4.2)
0 ≤ first_<index_type, k>(slices...)
0 ≤ last_<k>(extents(), slices...)
0 ≤ extents().extent(k)

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

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( $s_{k}$ .stride) if $S_{k}$ is a specialization of strided_slice and $s_{k}$ .stride < $s_{k}$ .extent;
(6.2)
otherwise, stride(k).

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

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

Returns:

(9.1)
submdspan_mapping_result{*this, 0}, if Extents::rank() == 0 is true;
(9.2)
otherwise, submdspan_mapping_result{layout_left::mapping(sub_ext), offset}, if
- (9.2.1)
  layout_type is layout_left; and
- (9.2.2)
  for each k in the range [0, SubExtents::rank() - 1)), is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (9.2.3)
  for k equal to SubExtents::rank() - 1, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true;
[Note 1:
If the above conditions are true, all $S_{k}$ with k larger than SubExtents::rank() - 1 are convertible to index_type.
— end note]
(9.3)
otherwise, submdspan_mapping_result{layout_right::mapping(sub_ext), offset}, if
- (9.3.1)
  layout_type is layout_right; and
- (9.3.2)
  for each k in the range [Extents::rank() - SubExtents::rank() + 1, Extents::rank()), is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (9.3.3)
  for k equal to Extents::rank() - SubExtents::rank(), $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true;
[Note 2:
If the above conditions are true, all $S_{k}$ with $k < Extents::rank() - SubExtents::rank()$ are convertible to index_type.
— end note]
(9.4)
otherwise, submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides),
offset}.