layout_right.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2023 Tobias Hienzsch
 
#ifndef TETL_MDSPAN_LAYOUT_RIGHT_HPP
#define TETL_MDSPAN_LAYOUT_RIGHT_HPP
 
#include <etl/_contracts/check.hpp>
#include <etl/_mdspan/extents.hpp>
#include <etl/_mdspan/is_extents.hpp>
#include <etl/_mdspan/layout.hpp>
#include <etl/_mdspan/submdspan_extents.hpp>
#include <etl/_mdspan/submdspan_mapping_result.hpp>
#include <etl/_type_traits/always_false.hpp>
#include <etl/_type_traits/is_convertible.hpp>
#include <etl/_type_traits/is_nothrow_constructible.hpp>
#include <etl/_utility/index_sequence.hpp>
 
namespace etl {
 
template <typename Extents>
struct layout_right::mapping {
    using extents_type = Extents;
    using index_type   = typename extents_type::index_type;
    using size_type    = typename extents_type::size_type;
    using rank_type    = typename extents_type::rank_type;
    using layout_type  = layout_right;
 
    // constructors
    constexpr mapping() noexcept               = default;
    constexpr mapping(mapping const&) noexcept = default;
 
    constexpr mapping(extents_type const& ext) noexcept
        : _extents{ext}
    {
    }
 
    template <typename OtherExtents>
        requires is_constructible_v<extents_type, OtherExtents>
    constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(
        mapping<OtherExtents> const& other
    ) noexcept
        : _extents{other.extents()}
    {
    }
 
    template <typename OtherExtents>
        requires(extents_type::rank() <= 1) && is_constructible_v<extents_type, OtherExtents>
    constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(
        layout_left::mapping<OtherExtents> const& other
    ) noexcept
        : _extents{other.extents()}
    {
    }
 
    template <typename OtherExtents>
    constexpr explicit(extents_type::rank() > 0) mapping(layout_stride::mapping<OtherExtents> const&) noexcept;
 
    constexpr auto operator=(mapping const&) noexcept -> mapping& = default;
 
    // observers
    [[nodiscard]] constexpr auto extents() const noexcept -> extents_type const&
    {
        return _extents;
    }
 
    [[nodiscard]] constexpr auto required_span_size() const noexcept -> index_type
    {
        return static_cast<index_type>(extents().fwd_prod_of_extents(extents_type::rank()));
    }
 
    template <typename... Indices>
        requires(sizeof...(Indices) == extents_type::rank())
            and (is_convertible_v<Indices, index_type> and ...)
            and (is_nothrow_constructible_v<index_type, Indices> and ...)
    [[nodiscard]] constexpr auto operator()(Indices... indices) const noexcept -> index_type
    {
        return [&]<size_t... Is>(index_sequence<Is...> /*seq*/) {
            return static_cast<index_type>(((static_cast<index_type>(indices) * stride(Is)) + ... + 0));
        }(index_sequence_for<Indices...>{});
    }
 
    [[nodiscard]] constexpr auto stride(rank_type r) const noexcept -> index_type
        requires(extents_type::rank() > 0)
    {
        TETL_PRECONDITION(r < extents_type::rank());
        return static_cast<index_type>(_extents.rev_prod_of_extents(r));
    }
 
    [[nodiscard]] static constexpr auto is_always_unique() noexcept -> bool
    {
        return true;
    }
    [[nodiscard]] static constexpr auto is_always_exhaustive() noexcept -> bool
    {
        return true;
    }
    [[nodiscard]] static constexpr auto is_always_strided() noexcept -> bool
    {
        return true;
    }
 
    [[nodiscard]] static constexpr auto is_unique() noexcept -> bool
    {
        return true;
    }
    [[nodiscard]] static constexpr auto is_exhaustive() noexcept -> bool
    {
        return true;
    }
    [[nodiscard]] static constexpr auto is_strided() noexcept -> bool
    {
        return true;
    }
 
    template <typename OtherExtents>
    friend constexpr auto operator==(mapping const& lhs, mapping<OtherExtents> const& rhs) noexcept -> bool
    {
        return lhs.extents() == rhs.extents();
    }
 
private:
    // template <typename... SliceSpecifiers>
    // [[nodiscard]] constexpr auto submdspan_mapping_impl(SliceSpecifiers... slices) const
    // {
    //     auto sub_ext     = etl::submdspan_extents(extents(), slices...);
    //     using SubExtents = decltype(sub_ext);
    //     static_assert(sizeof(SubExtents) > 0);
 
    // // auto sub_strides = {};
 
    // if constexpr (Extents::rank() == 0) {
    //     return etl::submdspan_mapping_result {*this, 0};
    // } else {
    //     static_assert(etl::always_false<SliceSpecifiers...>);
    // }
    // }
 
    // template <typename... SliceSpecifiers>
    // friend constexpr auto submdspan_mapping(mapping const& src, SliceSpecifiers... slices)
    // {
    //     return src.submdspan_mapping_impl(slices...);
    // }
 
    TETL_NO_UNIQUE_ADDRESS extents_type _extents{};
};
 
} // namespace etl
 
#endif // TETL_MDSPAN_LAYOUT_RIGHT_HPP