cuda_toolkit/include/thrust/system/cuda/detail/reverse.h

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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

#if THRUST_DEVICE_COMPILER == THRUST_DEVICE_COMPILER_NVCC
#include <thrust/system/cuda/detail/execution_policy.h>

THRUST_NAMESPACE_BEGIN
namespace cuda_cub {

template <class Derived, class ItemsIt, class ResultIt>
ResultIt __host__ __device__
reverse_copy(execution_policy<Derived> &policy,
             ItemsIt                    first,
             ItemsIt                    last,
             ResultIt                   result);

template <class Derived, class ItemsIt>
void __host__ __device__
reverse(execution_policy<Derived> &policy,
        ItemsIt                    first,
        ItemsIt                    last);

}    // namespace cuda_cub
THRUST_NAMESPACE_END

#include <thrust/advance.h>
#include <thrust/distance.h>
#include <thrust/system/cuda/detail/swap_ranges.h>
#include <thrust/system/cuda/detail/copy.h>
#include <thrust/iterator/reverse_iterator.h>

THRUST_NAMESPACE_BEGIN
namespace cuda_cub {

template <class Derived,
          class ItemsIt,
          class ResultIt>
ResultIt __host__ __device__
reverse_copy(execution_policy<Derived> &policy,
             ItemsIt                    first,
             ItemsIt                    last,
             ResultIt                   result)
{
  return cuda_cub::copy(policy,
                        thrust::make_reverse_iterator(last),
                        thrust::make_reverse_iterator(first),
                        result);
}

template <class Derived,
          class ItemsIt>
void __host__ __device__
reverse(execution_policy<Derived> &policy,
        ItemsIt                    first,
        ItemsIt                    last)
{
  typedef typename thrust::iterator_difference<ItemsIt>::type difference_type;

  // find the midpoint of [first,last)
  difference_type N = thrust::distance(first, last);
  ItemsIt mid(first);
  thrust::advance(mid, N / 2);

  cuda_cub::swap_ranges(policy, first, mid, thrust::make_reverse_iterator(last));
}


}    // namespace cuda_cub
THRUST_NAMESPACE_END
#endif