cuda_toolkit/include/thrust/system/cuda/detail/find.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/config.h>

#include <thrust/system/cuda/detail/execution_policy.h>
#include <thrust/detail/minmax.h>
#include <thrust/distance.h>

THRUST_NAMESPACE_BEGIN
namespace cuda_cub {

// XXX forward declare to circumvent circular depedency
template <class Derived,
          class InputIt,
          class Predicate>
InputIt __host__ __device__
find_if(execution_policy<Derived>& policy,
        InputIt                    first,
        InputIt                    last,
        Predicate                  predicate);

template <class Derived,
          class InputIt,
          class Predicate>
InputIt __host__ __device__
find_if_not(execution_policy<Derived>& policy,
            InputIt                    first,
            InputIt                    last,
            Predicate                  predicate);

template <class Derived,
          class InputIt,
          class T>
InputIt __host__ __device__
find(execution_policy<Derived> &policy,
     InputIt                    first,
     InputIt                    last,
     T const& value);

}; // namespace cuda_cub
THRUST_NAMESPACE_END

#include <thrust/system/cuda/detail/reduce.h>
#include <thrust/iterator/zip_iterator.h>

THRUST_NAMESPACE_BEGIN
namespace cuda_cub {

namespace __find_if {

  template <typename TupleType>
  struct functor
  {
    THRUST_DEVICE_FUNCTION TupleType
    operator()(const TupleType& lhs, const TupleType& rhs) const
    {
      // select the smallest index among true results
      if (thrust::get<0>(lhs) && thrust::get<0>(rhs))
      {
        return TupleType(true, (thrust::min)(thrust::get<1>(lhs), thrust::get<1>(rhs)));
      }
      else if (thrust::get<0>(lhs))
      {
        return lhs;
      }
      else
      {
        return rhs;
      }
    }
  };
}    // namespace __find_if

template <class Derived,
          class InputIt,
          class Size,
          class Predicate>
InputIt __host__ __device__
find_if_n(execution_policy<Derived>& policy,
          InputIt                    first,
          Size                       num_items,
          Predicate                  predicate)
{
  typedef typename thrust::tuple<bool,Size> result_type;

  // empty sequence
  if(num_items == 0) return first;

  // this implementation breaks up the sequence into separate intervals
  // in an attempt to early-out as soon as a value is found
  //
  // XXX compose find_if from a look-back prefix scan algorithm
  //     and abort kernel when the first element is found


  // TODO incorporate sizeof(InputType) into interval_threshold and round to multiple of 32
  const Size interval_threshold = 1 << 20;
  const Size interval_size = (thrust::min)(interval_threshold, num_items);

  // force transform_iterator output to bool
  typedef transform_input_iterator_t<bool,
                                     InputIt,
                                     Predicate>
      XfrmIterator;
  typedef thrust::tuple<XfrmIterator,
                        counting_iterator_t<Size> >
      IteratorTuple;
  typedef thrust::zip_iterator<IteratorTuple> ZipIterator;

  IteratorTuple iter_tuple =
      thrust::make_tuple(XfrmIterator(first, predicate),
                         counting_iterator_t<Size>(0));

  ZipIterator begin = thrust::make_zip_iterator(iter_tuple);
  ZipIterator end   = begin + num_items;

  for (ZipIterator interval_begin = begin;
       interval_begin < end;
       interval_begin += interval_size)
  {
    ZipIterator interval_end = interval_begin + interval_size;
    if(end < interval_end)
    {
      interval_end = end;
    } // end if

    result_type result = reduce(policy,
                                interval_begin,
                                interval_end,
                                result_type(false, interval_end - begin),
                                __find_if::functor<result_type>());

    // see if we found something
    if(thrust::get<0>(result))
    {
      return first + thrust::get<1>(result);
    }
  }

  //nothing was found if we reach here...
  return first + num_items;
}

template <class Derived,
          class InputIt,
          class Predicate>
InputIt __host__ __device__
find_if(execution_policy<Derived>& policy,
        InputIt                    first,
        InputIt                    last,
        Predicate                  predicate)
{
  return cuda_cub::find_if_n(policy, first, thrust::distance(first,last), predicate);
}

template <class Derived,
          class InputIt,
          class Predicate>
InputIt __host__ __device__
find_if_not(execution_policy<Derived>& policy,
            InputIt                    first,
            InputIt                    last,
            Predicate                  predicate)
{
  return cuda_cub::find_if(policy, first, last, thrust::detail::not1(predicate));
}


template <class Derived,
          class InputIt,
          class T>
InputIt __host__ __device__
find(execution_policy<Derived> &policy,
     InputIt                    first,
     InputIt                    last,
     T const& value)
{
  using thrust::placeholders::_1;

  return cuda_cub::find_if(policy,
                        first,
                        last,
                        _1 == value);
}


} // namespace cuda_cub
THRUST_NAMESPACE_END
#endif