24 Containers library [containers]

24.7 Views [views]

24.7.3 Multidimensional access [views.multidim]

24.7.3.7 submdspan [mdspan.sub]

24.7.3.7.6 Specializations of submdspan_mapping [mdspan.sub.map]

24.7.3.7.6.1 Common [mdspan.sub.map.common]

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

Constraints: sizeof...(slices) equals extents_type::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, $s_{k}$ .extent is equal to zero or $s_{k}$ .stride is greater than zero; and
(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 is true;
(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.

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...)...).

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

🔗

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

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< $S_{k}$ , full_extent_t> is true; and
- (1.3.2)
  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]
(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 $S_{p}$ models index-pair-like<index_type> or is_convertible_v< $S_{p}$ , full_extent_t> is true, the following conditions are met:
- (1.4.1)
  $S_{0}$ models index-pair-like<index_type> or is_convertible_v< $S_{0}$ , full_extent_t> is true; and
- (1.4.2)
  for each k in the range [u + 1, u + SubExtents::rank() - 1), is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (1.4.3)
  for k equal to u + SubExtents::rank() - 1, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true;
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 values static_extent(k) for k in the range [0, u + 1);
(1.5)
otherwise, submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}

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

🔗

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

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< $S_{k}$ , full_extent_t> is true; and
- (1.3.2)
  for k equal to _rank - SubExtents::rank(), $S_{k}$ 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 $k<\class{textit}{\texttt{_rank}} - SubExtents::rank()$ 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 $S_{p}$ models index-pair-like<index_type> or is_convertible_v< $S_{p}$ , full_extent_t> is true, the following conditions are met:
- (1.4.1)
  for k equal to rank_ - 1, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (1.4.2)
  for each k in the range [rank_ - SubExtents::rank() - u + 1, rank_ - u - 1), is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (1.4.3)
  for k equal to rank_ - SubExtents::rank() - u, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true;
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 values static_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}

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

🔗

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

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}

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

🔗

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

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 or SubExtents::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)
  $S_{0}$ models index-pair-like<index_type> or is_convertible_v< $S_{0}$ , full_extent_t> is true;
(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 $S_{p}$ models index-pair-like<index_type> or is_convertible_v< $S_{p}$ , full_extent_t> is true, the following conditions are met:
- (1.4.1)
  $S_{0}$ models index-pair-like<index_type> or is_convertible_v< $S_{0}$ , full_extent_t> is true; and
- (1.4.2)
  for each k in the range [u + 1, u + SubExtents::rank() - 1), is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (1.4.3)
  for k equal to u + SubExtents::rank() - 1, $S_{k}$ models index-pair-like<index_type> or is_convertible_v<Sk, full_extent_t> is true;
where S_static is:
- (1.4.4)
  dynamic_extent, if static-padding-stride is dynamic_extent or static_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}

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

🔗

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

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 or SubExtents::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, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true;
(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 $S_{p}$ models index-pair-like<index_type> or is_convertible_v< $S_{p}$ , full_extent_t> is true, the following conditions are met:
- (1.4.1)
  for k equal to rank_ - 1, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (1.4.2)
  for each k in the range [rank_ - SubExtents::rank() - u + 1, rank_ - u - 1)), is_convertible_v< $S_{k}$ , full_extent_t> is true; and
- (1.4.3)
  for k equal to rank_ - SubExtents::rank() - u, $S_{k}$ models index-pair-like<index_type> or is_convertible_v< $S_{k}$ , full_extent_t> is true;
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}