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#ifndef ROCPRIM_DEVICE_DEVICE_SEGMENTED_REDUCE_HPP_
#define ROCPRIM_DEVICE_DEVICE_SEGMENTED_REDUCE_HPP_

#include <iostream>
#include <iterator>
#include <type_traits>

#include "../common.hpp"
#include "../config.hpp"
#include "../detail/various.hpp"
#include "../functional.hpp"

#include "detail/config/device_segmented_reduce.hpp"
#include "detail/device_segmented_reduce.hpp"
#include "rocprim/type_traits.hpp"

BEGIN_ROCPRIM_NAMESPACE

/// \addtogroup devicemodule
/// @{

namespace detail
{

template<class Config,
         class InputIterator,
         class OutputIterator,
         class OffsetIterator,
         class InitValueType,
         class BinaryFunction>
inline hipError_t segmented_reduce_impl(void*          temporary_storage,
                                        size_t&        storage_size,
                                        InputIterator  input,
                                        OutputIterator output,
                                        unsigned int   segments,
                                        OffsetIterator begin_offsets,
                                        OffsetIterator end_offsets,
                                        BinaryFunction reduce_op,
                                        InitValueType  initial_value,
                                        hipStream_t    stream,
                                        bool           debug_synchronous)
{
    using input_type  = typename std::iterator_traits<InputIterator>::value_type;
    using result_type = ::rocprim::accumulator_t<BinaryFunction, input_type>;

    using config = wrapped_segmented_reduce_config<Config, result_type>;

    detail::target_arch target_arch;
    hipError_t          result = host_target_arch(stream, target_arch);
    if(result != hipSuccess)
    {
        return result;
    }
    const reduce_config_params params = dispatch_target_arch<config, false>(target_arch);

    const unsigned int block_size = params.kernel_config.block_size;

    if(temporary_storage == nullptr)
    {
        // Make sure user won't try to allocate 0 bytes memory, because
        // hipMalloc will return nullptr when size is zero.
        storage_size = 4;
        return hipSuccess;
    }

    if(segments == 0u)
        return hipSuccess;

    std::chrono::steady_clock::time_point start;

    if(debug_synchronous)
    {
        start = std::chrono::steady_clock::now();
    }
    auto segmented_reduce_kernel = [=](auto arch_config)
    {
        segmented_reduce<decltype(arch_config)>(input,
                                                output,
                                                begin_offsets,
                                                end_offsets,
                                                reduce_op,
                                                static_cast<result_type>(initial_value));
    };

    ROCPRIM_RETURN_ON_ERROR(execute_launch_plan<config>(target_arch,
                                                        segmented_reduce_kernel,
                                                        dim3(segments),
                                                        dim3(block_size),
                                                        0,
                                                        stream));
    ROCPRIM_DETAIL_HIP_SYNC_AND_RETURN_ON_ERROR("segmented_reduce", segments, start);

    return hipSuccess;
}

} // namespace detail

/// \brief Parallel segmented reduction primitive for device level.
///
/// segmented_reduce function performs a device-wide reduction operation across multiple sequences
/// using binary \p reduce_op operator.
///
/// \par Overview
/// * Returns the required size of \p temporary_storage in \p storage_size
/// if \p temporary_storage in a null pointer.
/// * Ranges specified by \p input must have at least \p size elements, \p output must have
/// \p segments elements.
/// * Ranges specified by \p begin_offsets and \p end_offsets must have
/// at least \p segments elements. They may use the same sequence <tt>offsets</tt> of at least
/// <tt>segments + 1</tt> elements: <tt>offsets</tt> for \p begin_offsets and
/// <tt>offsets + 1</tt> for \p end_offsets.
///
/// \tparam Config [optional] Configuration of the primitive, must be `default_config` or `reduce_config`.
/// \tparam InputIterator random-access iterator type of the input range. Must meet the
/// requirements of a C++ InputIterator concept. It can be a simple pointer type.
/// \tparam OutputIterator random-access iterator type of the output range. Must meet the
/// requirements of a C++ OutputIterator concept. It can be a simple pointer type.
/// \tparam OffsetIterator random-access iterator type of segment offsets. Must meet the
/// requirements of a C++ OutputIterator concept. It can be a simple pointer type.
/// \tparam BinaryFunction type of binary function used for reduction. Default type
/// is \p rocprim::plus<T>, where \p T is a \p value_type of \p InputIterator.
/// \tparam InitValueType type of the initial value.
///
/// \param [in] temporary_storage pointer to a device-accessible temporary storage. When
/// a null pointer is passed, the required allocation size (in bytes) is written to
/// \p storage_size and function returns without performing the reduction operation.
/// \param [in,out] storage_size reference to a size (in bytes) of \p temporary_storage.
/// \param [in] input iterator to the first element in the range to reduce.
/// \param [out] output iterator to the first element in the output range.
/// \param [in] segments number of segments in the input range.
/// \param [in] begin_offsets iterator to the first element in the range of beginning offsets.
/// \param [in] end_offsets iterator to the first element in the range of ending offsets.
/// \param [in] initial_value initial value to start the reduction.
/// \param [in] reduce_op binary operation function object that will be used for reduction.
/// The signature of the function should be equivalent to the following:
/// <tt>T f(const T &a, const T &b);</tt>. The signature does not need to have
/// <tt>const &</tt>, but function object must not modify the objects passed to it.
/// The default value is \p BinaryFunction().
/// \param [in] stream [optional] HIP stream object. The default is \p 0 (default stream).
/// \param [in] debug_synchronous [optional] If true, synchronization after every kernel
/// launch is forced in order to check for errors. The default value is \p false.
///
/// \returns \p hipSuccess (\p 0) after successful reduction; otherwise a HIP runtime error of
/// type \p hipError_t.
///
/// \par Example
/// \parblock
/// In this example a device-level segmented min-reduction operation is performed on an array of
/// integer values (<tt>short</tt>s are reduced into <tt>int</tt>s) using custom operator.
///
/// \code{.cpp}
/// #include <rocprim/rocprim.hpp>
///
/// // custom reduce function
/// auto min_op =
///     [] (int a, int b) -> int
///     {
///         return a < b ? a : b;
///     };
///
/// // Prepare input and output (declare pointers, allocate device memory etc.)
/// unsigned int segments;   // e.g., 3
/// short * input;           // e.g., [4, 7, 6, 2, 5, 1, 3, 8]
/// int * output;            // empty array of 3 elements
/// int * offsets;           // e.g. [0, 2, 3, 8]
/// int init_value;          // e.g., 9
///
/// size_t temporary_storage_size_bytes;
/// void * temporary_storage_ptr = nullptr;
/// // Get required size of the temporary storage
/// rocprim::segmented_reduce(
///     temporary_storage_ptr, temporary_storage_size_bytes,
///     input, output,
///     segments, offsets, offsets + 1,
///     min_op, init_value
/// );
///
/// // allocate temporary storage
/// hipMalloc(&temporary_storage_ptr, temporary_storage_size_bytes);
///
/// // perform segmented reduction
/// rocprim::segmented_reduce(
///     temporary_storage_ptr, temporary_storage_size_bytes,
///     input, output,
///     segments, offsets, offsets + 1,
///     min_op, init_value
/// );
/// // output: [4, 6, 1]
/// \endcode
/// \endparblock
template<class Config = default_config,
         class InputIterator,
         class OutputIterator,
         class OffsetIterator,
         class BinaryFunction
         = ::rocprim::plus<typename std::iterator_traits<InputIterator>::value_type>,
         class InitValueType = typename std::iterator_traits<InputIterator>::value_type>
inline hipError_t segmented_reduce(void*          temporary_storage,
                                   size_t&        storage_size,
                                   InputIterator  input,
                                   OutputIterator output,
                                   unsigned int   segments,
                                   OffsetIterator begin_offsets,
                                   OffsetIterator end_offsets,
                                   BinaryFunction reduce_op         = BinaryFunction(),
                                   InitValueType  initial_value     = InitValueType(),
                                   hipStream_t    stream            = 0,
                                   bool           debug_synchronous = false)
{
    return detail::segmented_reduce_impl<Config>(temporary_storage,
                                                 storage_size,
                                                 input,
                                                 output,
                                                 segments,
                                                 begin_offsets,
                                                 end_offsets,
                                                 reduce_op,
                                                 initial_value,
                                                 stream,
                                                 debug_synchronous);
}

/// @}
// end of group devicemodule

END_ROCPRIM_NAMESPACE

#endif // ROCPRIM_DEVICE_DEVICE_SEGMENTED_REDUCE_HPP_
