text: /******************************************************************************
   * Copyright (c) 2016, NVIDIA CORPORATION.  All rights reserved.
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   *     * Redistributions of source code must retain the above copyright
   *       notice, this list of conditions and the following disclaimer.
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   *       notice, this list of conditions and the following disclaimer in the
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   *     * Neither the name of the NVIDIA CORPORATION nor the
   *       names of its contributors may be used to endorse or promote products
   *       derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL NVIDIA CORPORATION BE LIABLE FOR ANY
   * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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   ******************************************************************************/
  #pragma once
  
  #include <thrust/detail/config.h>
  
  #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
  