sparse_discrete_domain.hpp

// Copyright (C) The DDC development team, see COPYRIGHT.md file
//
// SPDX-License-Identifier: MIT
 
#pragma once
 
#include <cstddef>
#include <functional>
#include <iterator>
#include <string>
#include <tuple>
#include <type_traits>
 
#include <Kokkos_Core.hpp>
 
#include "detail/tagged_vector.hpp"
#include "detail/type_seq.hpp"
 
#include "discrete_element.hpp"
#include "discrete_vector.hpp"
 
namespace ddc {
 
template <class... DDims>
class SparseDiscreteDomain;
 
template <class T>
struct is_sparse_discrete_domain : std::false_type
{
};
 
template <class... Tags>
struct is_sparse_discrete_domain<SparseDiscreteDomain<Tags...>> : std::true_type
{
};
 
template <class T>
inline constexpr bool is_sparse_discrete_domain_v = is_sparse_discrete_domain<T>::value;
 
namespace concepts {
 
template <class T>
concept sparse_discrete_domain = is_sparse_discrete_domain_v<T>;
 
}
 
namespace detail {
 
template <class... Tags>
struct ToTypeSeq<SparseDiscreteDomain<Tags...>>
{
    using type = TypeSeq<Tags...>;
};
 
template <class... DDims, class... ODDims>
struct Rebind<SparseDiscreteDomain<DDims...>, detail::TypeSeq<ODDims...>>
{
    using type = SparseDiscreteDomain<ODDims...>;
};
 
template <class InputIt1, class InputIt2>
KOKKOS_FUNCTION bool equal(InputIt1 first1, InputIt1 last1, InputIt2 first2)
{
    for (; first1 != last1; ++first1, ++first2) {
        if (!(*first1 == *first2)) {
            return false;
        }
    }
 
    return true;
}
 
template <class ForwardIt, class T = std::iterator_traits<ForwardIt>::value_type, class Compare>
KOKKOS_FUNCTION ForwardIt lower_bound(ForwardIt first, ForwardIt last, T const& value, Compare comp)
{
    ForwardIt it;
    typename std::iterator_traits<ForwardIt>::difference_type count = last - first;
    while (count > 0) {
        it = first;
        typename std::iterator_traits<ForwardIt>::difference_type const step = count / 2;
        it += step;
 
        if (comp(*it, value)) {
            first = ++it;
            count -= step + 1;
        } else {
            count = step;
        }
    }
 
    return first;
}
 
template <class ForwardIt, class T = std::iterator_traits<ForwardIt>::value_type, class Compare>
KOKKOS_FUNCTION bool binary_search(ForwardIt first, ForwardIt last, T const& value, Compare comp)
{
    first = ::ddc::detail::lower_bound(first, last, value, comp);
    return (!(first == last) && !(comp(value, *first)));
}
 
template <class DDim>
Kokkos::View<DiscreteElementType*, Kokkos::SharedSpace> extract_uid(
        Kokkos::DefaultExecutionSpace const& exec_space,
        Kokkos::View<DiscreteElement<DDim>*, Kokkos::SharedSpace> const& input)
{
    Kokkos::View<DiscreteElementType*, Kokkos::SharedSpace> output(input.label(), input.size());
    Kokkos::parallel_for(
            "SparseDiscreteDomainCtor",
            Kokkos::RangePolicy<
                    Kokkos::DefaultExecutionSpace,
                    Kokkos::IndexType<std::size_t>>(exec_space, 0, output.size()),
            KOKKOS_LAMBDA(std::size_t const i) { output(i) = input(i).uid(); });
    return output;
}
 
} // namespace detail
 
template <class... DDims>
class SparseDiscreteDomain
{
    template <class...>
    friend class SparseDiscreteDomain;
 
    static_assert(
            type_seq_is_unique_v<detail::TypeSeq<DDims...>>,
            "The dimensions of a SparseDiscreteDomain must be unique");
 
public:
    using discrete_element_type = DiscreteElement<DDims...>;
 
    using discrete_vector_type = DiscreteVector<DDims...>;
 
private:
    detail::TaggedVector<Kokkos::View<DiscreteElementType*, Kokkos::SharedSpace>, DDims...> m_views;
 
public:
    static KOKKOS_FUNCTION constexpr std::size_t rank()
    {
        return sizeof...(DDims);
    }
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain() = default;
 
    /// Construct a SparseDiscreteDomain by copies and merge of domains
    template <concepts::sparse_discrete_domain... DDoms>
    KOKKOS_FUNCTION constexpr explicit SparseDiscreteDomain(DDoms const&... domains)
        : m_views(domains.m_views...)
    {
    }
 
    /** Construct a SparseDiscreteDomain with Kokkos::View explicitly listing the discrete elements.
     * @param views list of Kokkos::View
     */
    explicit SparseDiscreteDomain(
            Kokkos::View<DiscreteElement<DDims>*, Kokkos::SharedSpace> const&... views)
    {
        Kokkos::DefaultExecutionSpace const exec_space;
        ((m_views[type_seq_rank_v<DDims, detail::TypeSeq<DDims...>>]
          = detail::extract_uid(exec_space, views)),
         ...);
        exec_space.fence("SparseDiscreteDomainCtor");
    }
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain(SparseDiscreteDomain const& x) = default;
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain(SparseDiscreteDomain&& x) = default;
 
    KOKKOS_DEFAULTED_FUNCTION ~SparseDiscreteDomain() = default;
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain& operator=(SparseDiscreteDomain const& x)
            = default;
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain& operator=(SparseDiscreteDomain&& x) = default;
 
    template <class... ODims>
    KOKKOS_FUNCTION constexpr bool operator==(SparseDiscreteDomain<ODims...> const& other) const
    {
        if constexpr ((std::is_same_v<DDims, ODims> && ...)) {
            if (empty() && other.empty()) {
                return true;
            }
            for (std::size_t i = 0; i < m_views.size(); ++i) {
                if (m_views[i].size() != other.m_views[i].size()) {
                    return false;
                }
                if (!detail::
                            equal(m_views[i].data(),
                                  m_views[i].data() + m_views[i].size(),
                                  other.m_views[i].data())) {
                    return false;
                }
            }
            return true;
        } else {
            return *this == SparseDiscreteDomain(other);
        }
    }
 
#if !defined(__cpp_impl_three_way_comparison) || __cpp_impl_three_way_comparison < 201902L
    // In C++20, `a!=b` shall be automatically translated by the compiler to `!(a==b)`
    template <class... ODims>
    KOKKOS_FUNCTION constexpr bool operator!=(SparseDiscreteDomain<ODims...> const& other) const
    {
        return !(*this == other);
    }
#endif
 
    KOKKOS_FUNCTION constexpr std::size_t size() const
    {
        return (1UL * ... * get<DDims>(m_views).size());
    }
 
    KOKKOS_FUNCTION constexpr discrete_vector_type extents() const noexcept
    {
        return discrete_vector_type(get<DDims>(m_views).size()...);
    }
 
    KOKKOS_FUNCTION constexpr auto discrete_elements() const noexcept
    {
        return m_views;
    }
 
    template <class QueryDDim>
    KOKKOS_FUNCTION constexpr DiscreteVector<QueryDDim> extent() const noexcept
    {
        return DiscreteVector<QueryDDim>(get<QueryDDim>(m_views).size());
    }
 
    KOKKOS_FUNCTION constexpr discrete_element_type front() const noexcept
    {
        return discrete_element_type(get<DDims>(m_views)(0)...);
    }
 
    KOKKOS_FUNCTION constexpr discrete_element_type back() const noexcept
    {
        return discrete_element_type(get<DDims>(m_views)(get<DDims>(m_views).size() - 1)...);
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain take_first(discrete_vector_type n) const
    {
        return SparseDiscreteDomain(front(), n);
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain take_last(discrete_vector_type n) const
    {
        return SparseDiscreteDomain(front() + prod(extents() - n), n);
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain remove_first(discrete_vector_type n) const
    {
        return SparseDiscreteDomain(front() + prod(n), extents() - n);
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain remove_last(discrete_vector_type n) const
    {
        return SparseDiscreteDomain(front(), extents() - n);
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain remove(
            discrete_vector_type n1,
            discrete_vector_type n2) const
    {
        return SparseDiscreteDomain(front() + prod(n1), extents() - n1 - n2);
    }
 
    KOKKOS_FUNCTION constexpr DiscreteElement<DDims...> operator()(
            DiscreteVector<DDims...> const& dvect) const noexcept
    {
        return DiscreteElement<DDims...>(get<DDims>(m_views)(get<DDims>(dvect))...);
    }
 
    template <class... DElems>
    KOKKOS_FUNCTION bool contains(DElems const&... delems) const noexcept
    {
        static_assert(
                sizeof...(DDims) == (0 + ... + DElems::size()),
                "Invalid number of dimensions");
        static_assert((is_discrete_element_v<DElems> && ...), "Expected DiscreteElements");
        DiscreteElement<DDims...> const delem(delems...);
        for (std::size_t i = 0; i < rank(); ++i) {
            if (!detail::binary_search(
                        m_views[i].data(),
                        m_views[i].data() + m_views[i].size(),
                        detail::array(delem)[i],
                        std::less {})) {
                return false;
            }
        }
        return true;
    }
 
    template <class... DElems>
    KOKKOS_FUNCTION DiscreteVector<DDims...> distance_from_front(
            DElems const&... delems) const noexcept
    {
        static_assert(
                sizeof...(DDims) == (0 + ... + DElems::size()),
                "Invalid number of dimensions");
        static_assert((is_discrete_element_v<DElems> && ...), "Expected DiscreteElements");
        KOKKOS_ASSERT(contains(delems...))
        return DiscreteVector<DDims...>(
                (detail::lower_bound(
                         get<DDims>(m_views).data(),
                         get<DDims>(m_views).data() + get<DDims>(m_views).size(),
                         uid<DDims>(take<DDims>(delems...)),
                         std::less {})
                 - get<DDims>(m_views).data())...);
    }
 
    KOKKOS_FUNCTION constexpr bool empty() const noexcept
    {
        return size() == 0;
    }
 
    KOKKOS_FUNCTION constexpr explicit operator bool()
    {
        return !empty();
    }
 
    KOKKOS_FUNCTION auto begin() const
        requires(sizeof...(DDims) == 1)
    {
        using DDim0 = std::tuple_element_t<0, std::tuple<DDims...>>;
        return get<DDim0>(m_views).data();
    }
 
    KOKKOS_FUNCTION auto end() const
        requires(sizeof...(DDims) == 1)
    {
        using DDim0 = std::tuple_element_t<0, std::tuple<DDims...>>;
        return get<DDim0>(m_views).data() + get<DDim0>(m_views).size();
    }
 
    KOKKOS_FUNCTION auto cbegin() const
        requires(sizeof...(DDims) == 1)
    {
        using DDim0 = std::tuple_element_t<0, std::tuple<DDims...>>;
        return get<DDim0>(m_views).data();
    }
 
    KOKKOS_FUNCTION auto cend() const
        requires(sizeof...(DDims) == 1)
    {
        using DDim0 = std::tuple_element_t<0, std::tuple<DDims...>>;
        return get<DDim0>(m_views).data() + get<DDim0>(m_views).size();
    }
 
    KOKKOS_FUNCTION constexpr decltype(auto) operator[](std::size_t n)
        requires(sizeof...(DDims) == 1)
    {
        return begin()[n];
    }
 
    KOKKOS_FUNCTION constexpr decltype(auto) operator[](std::size_t n) const
        requires(sizeof...(DDims) == 1)
    {
        return begin()[n];
    }
};
 
template <>
class SparseDiscreteDomain<>
{
    template <class...>
    friend class SparseDiscreteDomain;
 
public:
    using discrete_element_type = DiscreteElement<>;
 
    using discrete_vector_type = DiscreteVector<>;
 
    static KOKKOS_FUNCTION constexpr std::size_t rank()
    {
        return 0;
    }
 
    KOKKOS_DEFAULTED_FUNCTION constexpr SparseDiscreteDomain() = default;
 
    // Construct a SparseDiscreteDomain from a reordered copy of `domain`
    template <class... ODDims>
    KOKKOS_FUNCTION constexpr explicit SparseDiscreteDomain(
            SparseDiscreteDomain<ODDims...> const& /*domain*/)
    {
    }
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain(SparseDiscreteDomain const& x) = default;
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain(SparseDiscreteDomain&& x) = default;
 
    KOKKOS_DEFAULTED_FUNCTION ~SparseDiscreteDomain() = default;
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain& operator=(SparseDiscreteDomain const& x)
            = default;
 
    KOKKOS_DEFAULTED_FUNCTION SparseDiscreteDomain& operator=(SparseDiscreteDomain&& x) = default;
 
    KOKKOS_FUNCTION constexpr bool operator==(SparseDiscreteDomain const& /*other*/) const
    {
        return true;
    }
 
#if !defined(__cpp_impl_three_way_comparison) || __cpp_impl_three_way_comparison < 201902L
    // In C++20, `a!=b` shall be automatically translated by the compiler to `!(a==b)`
    KOKKOS_FUNCTION constexpr bool operator!=(SparseDiscreteDomain const& other) const
    {
        return !(*this == other);
    }
#endif
 
    static KOKKOS_FUNCTION constexpr std::size_t size()
    {
        return 1;
    }
 
    static KOKKOS_FUNCTION constexpr discrete_vector_type extents() noexcept
    {
        return {};
    }
 
    static KOKKOS_FUNCTION constexpr discrete_element_type front() noexcept
    {
        return {};
    }
 
    static KOKKOS_FUNCTION constexpr discrete_element_type back() noexcept
    {
        return {};
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain take_first(discrete_vector_type /*n*/) const
    {
        return *this;
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain take_last(discrete_vector_type /*n*/) const
    {
        return *this;
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain remove_first(discrete_vector_type /*n*/) const
    {
        return *this;
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain remove_last(discrete_vector_type /*n*/) const
    {
        return *this;
    }
 
    KOKKOS_FUNCTION constexpr SparseDiscreteDomain remove(
            discrete_vector_type /*n1*/,
            discrete_vector_type /*n2*/) const
    {
        return *this;
    }
 
    KOKKOS_FUNCTION constexpr DiscreteElement<> operator()(
            DiscreteVector<> const& /*dvect*/) const noexcept
    {
        return {};
    }
 
    static KOKKOS_FUNCTION bool contains() noexcept
    {
        return true;
    }
 
    static KOKKOS_FUNCTION bool contains(DiscreteElement<>) noexcept
    {
        return true;
    }
 
    static KOKKOS_FUNCTION DiscreteVector<> distance_from_front() noexcept
    {
        return {};
    }
 
    static KOKKOS_FUNCTION DiscreteVector<> distance_from_front(DiscreteElement<>) noexcept
    {
        return {};
    }
 
    static KOKKOS_FUNCTION constexpr bool empty() noexcept
    {
        return false;
    }
 
    KOKKOS_FUNCTION constexpr explicit operator bool()
    {
        return true;
    }
};
 
template <class... QueryDDims, class... DDims>
KOKKOS_FUNCTION constexpr SparseDiscreteDomain<QueryDDims...> select(
        SparseDiscreteDomain<DDims...> const& domain)
{
    return SparseDiscreteDomain<QueryDDims...>(domain);
}
 
namespace detail {
 
template <class T>
struct ConvertTypeSeqToSparseDiscreteDomain
{
};
 
template <class... DDims>
struct ConvertTypeSeqToSparseDiscreteDomain<detail::TypeSeq<DDims...>>
{
    using type = SparseDiscreteDomain<DDims...>;
};
 
template <class T>
using convert_type_seq_to_sparse_discrete_domain_t = ConvertTypeSeqToSparseDiscreteDomain<T>::type;
 
} // namespace detail
 
// Computes the subtraction DDom_a - DDom_b in the sense of linear spaces(retained dimensions are those in DDom_a which are not in DDom_b)
template <class... DDimsA, class... DDimsB>
KOKKOS_FUNCTION constexpr auto remove_dims_of(
        SparseDiscreteDomain<DDimsA...> const& DDom_a,
        SparseDiscreteDomain<DDimsB...> const& /*DDom_b*/) noexcept
{
    using TagSeqA = detail::TypeSeq<DDimsA...>;
    using TagSeqB = detail::TypeSeq<DDimsB...>;
 
    using type_seq_r = type_seq_remove_t<TagSeqA, TagSeqB>;
    return detail::convert_type_seq_to_sparse_discrete_domain_t<type_seq_r>(DDom_a);
}
 
//! Remove the dimensions DDimsB from DDom_a
//! @param[in] DDom_a The discrete domain on which to remove dimensions
//! @return The discrete domain without DDimsB dimensions
template <class... DDimsB, class... DDimsA>
KOKKOS_FUNCTION constexpr auto remove_dims_of(
        SparseDiscreteDomain<DDimsA...> const& DDom_a) noexcept
{
    using TagSeqA = detail::TypeSeq<DDimsA...>;
    using TagSeqB = detail::TypeSeq<DDimsB...>;
 
    using type_seq_r = type_seq_remove_t<TagSeqA, TagSeqB>;
    return detail::convert_type_seq_to_sparse_discrete_domain_t<type_seq_r>(DDom_a);
}
 
namespace detail {
 
// Checks if dimension of DDom_a is DDim1. If not, returns restriction to DDim2 of DDom_b. May not be useful in its own, it helps for replace_dim_of
template <typename DDim1, typename DDim2, typename DDimA, typename... DDimsB>
KOKKOS_FUNCTION constexpr std::conditional_t<
        std::is_same_v<DDimA, DDim1>,
        ddc::SparseDiscreteDomain<DDim2>,
        ddc::SparseDiscreteDomain<DDimA>>
replace_dim_of_1d(
        [[maybe_unused]] SparseDiscreteDomain<DDimA> const& DDom_a,
        [[maybe_unused]] SparseDiscreteDomain<DDimsB...> const& DDom_b) noexcept
{
    if constexpr (std::is_same_v<DDimA, DDim1>) {
        return ddc::SparseDiscreteDomain<DDim2>(DDom_b);
    } else {
        return DDom_a;
    }
}
 
} // namespace detail
 
// Replace in DDom_a the dimension Dim1 by the dimension Dim2 of DDom_b
template <typename DDim1, typename DDim2, typename... DDimsA, typename... DDimsB>
KOKKOS_FUNCTION constexpr auto replace_dim_of(
        SparseDiscreteDomain<DDimsA...> const& DDom_a,
        [[maybe_unused]] SparseDiscreteDomain<DDimsB...> const& DDom_b) noexcept
{
    // TODO : static_asserts
    using TagSeqA = detail::TypeSeq<DDimsA...>;
    using TagSeqB = detail::TypeSeq<DDim1>;
    using TagSeqC = detail::TypeSeq<DDim2>;
 
    using type_seq_r = ddc::type_seq_replace_t<TagSeqA, TagSeqB, TagSeqC>;
    return ddc::detail::convert_type_seq_to_sparse_discrete_domain_t<type_seq_r>(
            detail::replace_dim_of_1d<
                    DDim1,
                    DDim2,
                    DDimsA,
                    DDimsB...>(ddc::SparseDiscreteDomain<DDimsA>(DDom_a), DDom_b)...);
}
 
template <class... QueryDDims, class... DDims>
KOKKOS_FUNCTION constexpr DiscreteVector<QueryDDims...> extents(
        SparseDiscreteDomain<DDims...> const& domain) noexcept
{
    return DiscreteVector<QueryDDims...>(SparseDiscreteDomain<QueryDDims>(domain).size()...);
}
 
template <class... QueryDDims, class... DDims>
KOKKOS_FUNCTION constexpr DiscreteElement<QueryDDims...> front(
        SparseDiscreteDomain<DDims...> const& domain) noexcept
{
    return DiscreteElement<QueryDDims...>(SparseDiscreteDomain<QueryDDims>(domain).front()...);
}
 
template <class... QueryDDims, class... DDims>
KOKKOS_FUNCTION constexpr DiscreteElement<QueryDDims...> back(
        SparseDiscreteDomain<DDims...> const& domain) noexcept
{
    return DiscreteElement<QueryDDims...>(SparseDiscreteDomain<QueryDDims>(domain).back()...);
}
 
} // namespace ddc