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:
Preconditions: For each rank index k of extents(), all of the following are true:
  • if is a specialization of strided_slice, .extent is equal to zero or .stride is greater than zero; and
  • 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:
  • stride(k) * de-ice(.stride) if is a specialization of strided_slice and .stride < .extent is true;
  • 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:
  • submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;
  • otherwise, submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if SubExtents​::​rank() == 0 is true;
  • otherwise, submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if
    • for each k in the range [0, SubExtents​::​rank() - 1)), is_convertible_v<, full_extent_t> is true; and
    • for k equal to SubExtents​::​rank() - 1, models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true;
    [Note 1: 
    If the above conditions are true, all with k larger than SubExtents​::​rank() - 1 are convertible to index_type.
    — end note]
  • otherwise, submdspan_mapping_result{layout_left_padded<S_static>::mapping(sub_ext, stride(u + 1)), offset} if for a value u for which is the smallest value p larger than zero for which models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true, the following conditions are met:
    • models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true; and
    • for each k in the range [u + 1, u + SubExtents​::​rank() - 1), is_convertible_v<, full_extent_t> is true; and
    • for k equal to u + SubExtents​::​rank() - 1, models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true;
    and where S_static is:
    • dynamic_extent, if static_extent(k) is dynamic_extent for any k in the range [0, u + 1),
    • otherwise, the product of all values static_extent(k) for k in the range [0, u + 1);
  • 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:
  • submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;
  • 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:
  • submdspan_mapping_result{*this, 0}, if Extents​::​rank() == 0 is true;
  • otherwise, submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if rank_ == 1 is true or SubExtents​::​rank() == 0 is true;
  • otherwise, submdspan_mapping_result{layout_left​::​mapping(sub_ext), offset}, if
  • 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 models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true, the following conditions are met:
    • models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true; and
    • for each k in the range [u + 1, u + SubExtents​::​rank() - 1), is_convertible_v<, full_extent_t> is true; and
    • for k equal to u + SubExtents​::​rank() - 1, models index-pair-like<index_type> or is_convertible_v<Sk, full_extent_t> is true;
    where S_static is:
    • 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),
    • otherwise, the product of static-padding-stride and all values static_extent(k) for k in the range [1, u + 1);
  • 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:
  • submdspan_mapping_result{*this, 0}, if rank_ == 0 is true;
  • otherwise, submdspan_mapping_result{layout_right​::​mapping(sub_ext), offset},
    if rank_ == 1 is true or SubExtents​::​rank() == 0 is true;
  • otherwise, submdspan_mapping_result{layout_right​::​mapping(sub_ext), offset}, if
    • SubExtents​::​rank() == 1 is true and
    • for k equal to rank_ - 1, models index-pair-like<index_type> or is_convertible_v< , full_extent_t> is true;
  • 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 models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true, the following conditions are met:
    • for k equal to rank_ - 1, models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true; and
    • for each k in the range [rank_ - SubExtents​::​rank() - u + 1, rank_ - u - 1)), is_convertible_v<, full_extent_t> is true; and
    • for k equal to rank_ - SubExtents​::​rank() - u, models index-pair-like<index_type> or is_convertible_v<, full_extent_t> is true;
    and where S_static is:
    • 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,
    • otherwise, the product of static-padding-stride and all values static_extent(k) with k in the range [rank_ - u - 1, rank_ - 1);
  • otherwise, submdspan_mapping_result{layout_stride::mapping(sub_ext, sub_strides), offset}