chip.hpp

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// SPDX-License-Identifier: BSD-2-Clause
 
#ifndef pRC_CORE_TENSOR_FUNCTIONS_CHIP_H
#define pRC_CORE_TENSOR_FUNCTIONS_CHIP_H
 
#include <prc/core/functors/view.hpp>
#include <prc/core/tensor/declarations.hpp>
#include <prc/core/tensor/views/chip.hpp>
 
namespace pRC
{
    template<Index... Ds, class X, IsConvertible<Index>... Is,
        IsTensorish R = RemoveReference<X>>
        requires(sizeof...(Is) == sizeof...(Ds)) &&
        requires { chip<Ds...>(typename R::Sizes()); }
    static inline constexpr auto chip(X &&a, Is const... indices)
    {
        if constexpr(IsInvocable<View, X>)
        {
            if constexpr(sizeof...(Ds) == 0)
            {
                return view(forward<X>(a));
            }
            else if constexpr(sizeof...(Ds) == 1)
            {
                using V = RemoveReference<decltype(view(forward<X>(a)))>;
                constexpr auto D = Sequence<Index, Ds...>::value(0);
                return TensorViews::Chip<typename R::Type,
                    decltype(chip<D>(typename R::Sizes())), D, V>(
                    view(forward<X>(a)), indices...);
            }
            else
            {
                return expand(
                    makeRange<Index, 1, sizeof...(Ds)>(),
                    [&a](auto const subscripts, auto const... seq)
                    {
                        using S = Sequence<Index, Ds...>;
                        return chip<((S::value(seq) < S::value(0))
                                ? S::value(seq)
                                : S::value(seq) - 1)...>(
                            chip<S::value(0)>(a, subscripts[0]),
                            subscripts[seq]...);
                    },
                    expand(select<Ds...>(typename R::Sizes()),
                        [indices...](auto const... seq)
                        {
                            return Subscripts<seq...>(indices...);
                        }));
            }
        }
        else
        {
            return eval(chip<Ds...>(a, indices...));
        }
    }
}
#endif // pRC_CORE_TENSOR_FUNCTIONS_CHIP_H