submdspan.hh

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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
#ifndef DUNE_COMMON_STD_SUBMDSPAN_HH
#define DUNE_COMMON_STD_SUBMDSPAN_HH
 
#include <array>
#include <tuple>
#include <type_traits>
 
#include <dune/common/indices.hh>
#include <dune/common/std/extents.hh>
#include <dune/common/std/impl/submdspan.hh>
#include <dune/common/std/mdspan.hh>
#include <dune/common/std/submdspan_slices.hh>
 
namespace Dune::Std {
 
template <class IndexType, std::size_t... exts, class... SliceSpecifiers,
  std::enable_if_t<(sizeof...(SliceSpecifiers) == sizeof...(exts)), int> = 0>
constexpr auto subextents (const extents<IndexType,exts...>& src, SliceSpecifiers... slices)
{
  using sub_extents_type = Impl::SubextentsType<extents<IndexType,exts...>,SliceSpecifiers...>;
  std::array<IndexType,sub_extents_type::rank()> sub_exts{};
  std::size_t j = 0;
  auto tuple = std::tuple<SliceSpecifiers...>{slices...};
  Dune::unpackIntegerSequence([&](auto... k) {
    auto add = [&](auto kk) {
      constexpr std::size_t i = decltype(kk)::value;
      using slice_type = std::tuple_element_t<i,decltype(tuple)>;
      if constexpr(Impl::is_kept_slice_v<slice_type>)
        sub_exts[j++] = Impl::slice_extent<i>(src, std::get<i>(tuple));
    };
    (add(std::integral_constant<std::size_t,k>{}), ...);
  }, std::index_sequence_for<SliceSpecifiers...>{});
  return sub_extents_type{sub_exts};
}
 
template <class Mapping, class... SliceSpecifiers,
  std::enable_if_t<(sizeof...(SliceSpecifiers) == Mapping::extents_type::rank()), int> = 0>
constexpr auto submdspan_mapping (const Mapping& mapping, SliceSpecifiers... slices)
{
  auto tuple = std::tuple<SliceSpecifiers...>{slices...};
  return Impl::make_sub_mapping(mapping, tuple, std::index_sequence_for<SliceSpecifiers...>{});
}
 
template <class ElementType, class Extents, class LayoutPolicy, class AccessorPolicy,
          class... SliceSpecifiers,
  std::enable_if_t<(sizeof...(SliceSpecifiers) == Extents::rank()), int> = 0>
constexpr auto submdspan (const mdspan<ElementType,Extents,LayoutPolicy,AccessorPolicy>& src,
                          SliceSpecifiers... slices)
{
  auto result = submdspan_mapping(src.mapping(), slices...);
  using mapping_type = decltype(result.mapping);
  using accessor_type = typename AccessorPolicy::offset_policy;
  return mdspan<ElementType, typename mapping_type::extents_type, typename mapping_type::layout_type, accessor_type>{
    src.accessor().offset(src.data_handle(), result.offset),
    result.mapping,
    accessor_type(src.accessor())};
}
 
} // end namespace Dune::Std
 
#endif // DUNE_COMMON_STD_SUBMDSPAN_HH