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#pragma once

#include <thrust/detail/config.h>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header
#include <thrust/detail/cpp14_required.h>

#if THRUST_CPP_DIALECT >= 2014

#if THRUST_DEVICE_COMPILER == THRUST_DEVICE_COMPILER_NVCC

#include <thrust/iterator/iterator_traits.h>

#include <thrust/system/cuda/config.h>
#include <thrust/system/cuda/detail/async/customization.h>
#include <thrust/system/cuda/detail/util.h>
#include <thrust/system/cuda/future.h>

#include <thrust/type_traits/remove_cvref.h>

#include <thrust/distance.h>

#include <type_traits>

// TODO specialize for thrust::plus to use e.g. ExclusiveSum instead of ExcScan
//  - Note that thrust::plus<> is transparent, cub::Sum is not. This should be
//    fixed in CUB first).
//  - Need to check if CUB actually optimizes for sums before putting in effort

THRUST_NAMESPACE_BEGIN
namespace system
{
namespace cuda
{
namespace detail
{

template <typename DerivedPolicy,
          typename ForwardIt,
          typename Size,
          typename OutputIt,
          typename InitialValueType,
          typename BinaryOp>
unique_eager_event
async_exclusive_scan_n(execution_policy<DerivedPolicy>& policy,
                       ForwardIt first,
                       Size n,
                       OutputIt out,
                       InitialValueType init,
                       BinaryOp op)
{
  using InputValueT = cub::detail::InputValue<InitialValueType>;
  using Dispatch32 = cub::DispatchScan<ForwardIt,
                                       OutputIt,
                                       BinaryOp,
                                       InputValueT,
                                       thrust::detail::int32_t,
                                       InitialValueType>;
  using Dispatch64 = cub::DispatchScan<ForwardIt,
                                       OutputIt,
                                       BinaryOp,
                                       InputValueT,
                                       thrust::detail::int64_t,
                                       InitialValueType>;

  InputValueT init_value(init);

  auto const device_alloc = get_async_device_allocator(policy);
  unique_eager_event ev;

  // Determine temporary device storage requirements.
  cudaError_t status;
  size_t tmp_size = 0;
  {
    THRUST_INDEX_TYPE_DISPATCH2(status,
                                Dispatch32::Dispatch,
                                Dispatch64::Dispatch,
                                n,
                                (nullptr,
                                  tmp_size,
                                  first,
                                  out,
                                  op,
                                  init_value,
                                  n_fixed,
                                  nullptr));
    thrust::cuda_cub::throw_on_error(status,
                                     "after determining tmp storage "
                                     "requirements for exclusive_scan");
  }

  // Allocate temporary storage.
  auto content = uninitialized_allocate_unique_n<thrust::detail::uint8_t>(
    device_alloc, tmp_size
  );
  void* const tmp_ptr = raw_pointer_cast(content.get());

  // Set up stream with dependencies.
  cudaStream_t const user_raw_stream = thrust::cuda_cub::stream(policy);

  if (thrust::cuda_cub::default_stream() != user_raw_stream)
  {
    ev = make_dependent_event(
      std::tuple_cat(
        std::make_tuple(
          std::move(content),
          unique_stream(nonowning, user_raw_stream)
        ),
        extract_dependencies(std::move(thrust::detail::derived_cast(policy)))));
  }
  else
  {
    ev = make_dependent_event(
      std::tuple_cat(
        std::make_tuple(std::move(content)),
        extract_dependencies(std::move(thrust::detail::derived_cast(policy)))));
  }

  // Run scan.
  {
    THRUST_INDEX_TYPE_DISPATCH2(status,
                                Dispatch32::Dispatch,
                                Dispatch64::Dispatch,
                                n,
                                (tmp_ptr,
                                  tmp_size,
                                  first,
                                  out,
                                  op,
                                  init_value,
                                  n_fixed,
                                  user_raw_stream));
    thrust::cuda_cub::throw_on_error(status,
                                     "after dispatching exclusive_scan kernel");
  }

  return ev;
}

}}} // namespace system::cuda::detail

namespace cuda_cub
{

// ADL entry point.
template <typename DerivedPolicy,
          typename ForwardIt,
          typename Sentinel,
          typename OutputIt,
          typename InitialValueType,
          typename BinaryOp>
auto async_exclusive_scan(execution_policy<DerivedPolicy>& policy,
                          ForwardIt first,
                          Sentinel&& last,
                          OutputIt&& out,
                          InitialValueType &&init,
                          BinaryOp&& op)
THRUST_RETURNS(
  thrust::system::cuda::detail::async_exclusive_scan_n(
    policy,
    first,
    distance(first, THRUST_FWD(last)),
    THRUST_FWD(out),
    THRUST_FWD(init),
    THRUST_FWD(op)
  )
)

} // namespace cuda_cub

THRUST_NAMESPACE_END

#endif // THRUST_DEVICE_COMPILER == THRUST_DEVICE_COMPILER_NVCC

#endif // C++14

