transform_reduce.hpp

// Copyright (C) The DDC development team, see COPYRIGHT.md file
//
// SPDX-License-Identifier: MIT
 
#pragma once
 
#include <utility>
 
#include "detail/macros.hpp"
 
#include "discrete_domain.hpp"
#include "discrete_element.hpp"
 
namespace ddc {
 
namespace detail {
 
/** A serial reduction over a nD domain
 * @param[in] domain the range over which to apply the algorithm
 * @param[in] neutral the neutral element of the reduction operation
 * @param[in] reduce a binary FunctionObject that will be applied in unspecified order to the
 *            results of transform, the results of other reduce and neutral.
 * @param[in] transform a unary FunctionObject that will be applied to each element of the input
 *            range. The return type must be acceptable as input to reduce
 * @param[in] dcoords discrete elements from dimensions already in a loop
 */
template <class Support, class T, class BinaryReductionOp, class UnaryTransformOp, class... DCoords>
T transform_reduce_serial(
        Support const& domain,
        [[maybe_unused]] T const neutral,
        BinaryReductionOp const& reduce,
        UnaryTransformOp const& transform,
        DCoords const&... dcoords) noexcept
{
    DDC_IF_NVCC_THEN_PUSH_AND_SUPPRESS(implicit_return_from_non_void_function)
    if constexpr (sizeof...(DCoords) == Support::rank()) {
        return transform(typename Support::discrete_element_type(dcoords...));
    } else {
        using CurrentDDim = type_seq_element_t<sizeof...(DCoords), to_type_seq_t<Support>>;
        T result = neutral;
        for (DiscreteElement<CurrentDDim> const ii : DiscreteDomain<CurrentDDim>(domain)) {
            result = reduce(
                    result,
                    transform_reduce_serial(domain, neutral, reduce, transform, dcoords..., ii));
        }
        return result;
    }
    DDC_IF_NVCC_THEN_POP
}
 
} // namespace detail
 
/** A reduction over a nD domain in serial
 * @param[in] domain the range over which to apply the algorithm
 * @param[in] neutral the neutral element of the reduction operation
 * @param[in] reduce a binary FunctionObject that will be applied in unspecified order to the
 *            results of transform, the results of other reduce and neutral.
 * @param[in] transform a unary FunctionObject that will be applied to each element of the input
 *            range. The return type must be acceptable as input to reduce
 */
template <class Support, class T, class BinaryReductionOp, class UnaryTransformOp>
T transform_reduce(
        Support const& domain,
        T neutral,
        BinaryReductionOp&& reduce,
        UnaryTransformOp&& transform) noexcept
{
    return detail::transform_reduce_serial(
            domain,
            neutral,
            std::forward<BinaryReductionOp>(reduce),
            std::forward<UnaryTransformOp>(transform));
}
 
} // namespace ddc