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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 _CCCL_STD_VER >= 2014

#  if THRUST_DEVICE_COMPILER == THRUST_DEVICE_COMPILER_NVCC

#    include <thrust/system/cuda/config.h>

#    include <thrust/distance.h>
#    include <thrust/iterator/iterator_traits.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 <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 detail
} // namespace cuda
} // namespace system

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