reduce.hpp

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// SPDX-License-Identifier: BSD-2-Clause
 
#ifndef pRC_CORE_TENSOR_FUNCTIONS_REDUCE_H
#define pRC_CORE_TENSOR_FUNCTIONS_REDUCE_H
 
#include <prc/core/functors/view.hpp>
#include <prc/core/tensor/declarations.hpp>
#include <prc/core/tensor/views/reduce.hpp>
 
namespace pRC
{
    template<class F, Index... Is, class X, IsTensorish R = RemoveReference<X>,
        class E = ResultOf<X, typename R::Subscripts>>
        requires(sizeof...(Is) <= R::Dimension && max(Is...) < R::Dimension) &&
        IsInvocable<F, E, E> &&
        IsInvocable<F, decltype(F::template Identity<typename R::Type>()), E> &&
        requires { chip<Is...>(typename R::Sizes()); }
    static inline constexpr auto reduce(X &&a)
    {
        if constexpr(IsInvocable<View, X>)
        {
            using V = RemoveReference<decltype(view(forward<X>(a)))>;
            using T = RemoveConstReference<ResultOf<F, E, E>>;
            using Sizes = decltype(chip<Is...>(typename R::Sizes()));
 
            return TensorViews::Reduce<T, Sizes, F,
                decltype(sort(Sequence<Index, Is...>())), V>(
                view(forward<X>(a)));
        }
        else
        {
            return eval(reduce<F, Is...>(a));
        }
    }
 
    template<class F, class X, IsTensorish R = RemoveReference<X>,
        class E = ResultOf<X, typename R::Subscripts>>
        requires IsInvocable<F, E, E> &&
        IsInvocable<F, decltype(F::template Identity<typename R::Type>()), E>
    static inline constexpr auto reduce(X &&a)
    {
        if constexpr(R::Dimension == 0)
        {
            if constexpr(!IsInvocable<View, X>)
            {
                return eval(forward<X>(a));
            }
            else
            {
                return view(forward<X>(a));
            }
        }
        else
        {
            return expand(makeSeries<Index, R::Dimension>(),
                [&a](auto const... seq)
                {
                    return reduce<F, seq...>(forward<X>(a));
                });
        }
    }
}
#endif // pRC_CORE_TENSOR_FUNCTIONS_REDUCE_H