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   * Copyright (c) 2011, Duane Merrill.  All rights reserved.
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  /**
   * \file
   * Random-access iterator types
   */
  
  #pragma once
  
  #include <iterator>
  #include <iostream>
  
  #include "../thread/thread_load.cuh"
  #include "../thread/thread_store.cuh"
  #include "../util_device.cuh"
  #include "../util_namespace.cuh"
  
  #include <thrust/version.h>
  
  #if (THRUST_VERSION >= 100700)
      // This iterator is compatible with Thrust API 1.7 and newer
      #include <thrust/iterator/iterator_facade.h>
      #include <thrust/iterator/iterator_traits.h>
  #endif // THRUST_VERSION
  
  /// Optional outer namespace(s)
  CUB_NS_PREFIX
  
  /// CUB namespace
  namespace cub {
  
  /**
   * \addtogroup UtilIterator
   * @{
   */
  
  
  /**
   * \brief A random-access input wrapper for pairing dereferenced values with their corresponding indices (forming \p KeyValuePair tuples).
   *
   * \par Overview
   * - ArgIndexInputIteratorTwraps a random access input iterator \p itr of type \p InputIteratorT.
   *   Dereferencing an ArgIndexInputIteratorTat offset \p i produces a \p KeyValuePair value whose
   *   \p key field is \p i and whose \p value field is <tt>itr[i]</tt>.
   * - Can be used with any data type.
   * - Can be constructed, manipulated, and exchanged within and between host and device
   *   functions.  Wrapped host memory can only be dereferenced on the host, and wrapped
   *   device memory can only be dereferenced on the device.
   * - Compatible with Thrust API v1.7 or newer.
   *
   * \par Snippet
   * The code snippet below illustrates the use of \p ArgIndexInputIteratorTto
   * dereference an array of doubles
   * \par
   * \code
   * #include <cub/cub.cuh>   // or equivalently <cub/iterator/arg_index_input_iterator.cuh>
   *
   * // Declare, allocate, and initialize a device array
   * double *d_in;         // e.g., [8.0, 6.0, 7.0, 5.0, 3.0, 0.0, 9.0]
   *
   * // Create an iterator wrapper
   * cub::ArgIndexInputIterator<double*> itr(d_in);
   *
   * // Within device code:
   * typedef typename cub::ArgIndexInputIterator<double*>::value_type Tuple;
   * Tuple item_offset_pair.key = *itr;
   * printf("%f @ %d
  ",
   *   item_offset_pair.value,
   *   item_offset_pair.key);   // 8.0 @ 0
   *
   * itr = itr + 6;
   * item_offset_pair.key = *itr;
   * printf("%f @ %d
  ",
   *   item_offset_pair.value,
   *   item_offset_pair.key);   // 9.0 @ 6
   *
   * \endcode
   *
   * \tparam InputIteratorT       The value type of the wrapped input iterator
   * \tparam OffsetT              The difference type of this iterator (Default: \p ptrdiff_t)
   * \tparam OutputValueT         The paired value type of the <offset,value> tuple (Default: value type of input iterator)
   */
  template <
      typename    InputIteratorT,
      typename    OffsetT             = ptrdiff_t,
      typename    OutputValueT        = typename std::iterator_traits<InputIteratorT>::value_type>
  class ArgIndexInputIterator
  {
  public:
  
      // Required iterator traits
      typedef ArgIndexInputIterator                       self_type;              ///< My own type
      typedef OffsetT                                     difference_type;        ///< Type to express the result of subtracting one iterator from another
      typedef KeyValuePair<difference_type, OutputValueT> value_type;             ///< The type of the element the iterator can point to
      typedef value_type*                                 pointer;                ///< The type of a pointer to an element the iterator can point to
      typedef value_type                                  reference;              ///< The type of a reference to an element the iterator can point to
  
  #if (THRUST_VERSION >= 100700)
      // Use Thrust's iterator categories so we can use these iterators in Thrust 1.7 (or newer) methods
      typedef typename thrust::detail::iterator_facade_category<
          thrust::any_system_tag,
          thrust::random_access_traversal_tag,
          value_type,
          reference
        >::type iterator_category;                                        ///< The iterator category
  #else
      typedef std::random_access_iterator_tag     iterator_category;      ///< The iterator category
  #endif  // THRUST_VERSION
  
  private:
  
      InputIteratorT  itr;
      difference_type offset;
  
  public:
  
      /// Constructor
      __host__ __device__ __forceinline__ ArgIndexInputIterator(
          InputIteratorT  itr,            ///< Input iterator to wrap
          difference_type offset = 0)     ///< OffsetT (in items) from \p itr denoting the position of the iterator
      :
          itr(itr),
          offset(offset)
      {}
  
      /// Postfix increment
      __host__ __device__ __forceinline__ self_type operator++(int)
      {
          self_type retval = *this;
          offset++;
          return retval;
      }
  
      /// Prefix increment
      __host__ __device__ __forceinline__ self_type operator++()
      {
          offset++;
          return *this;
      }
  
      /// Indirection
      __host__ __device__ __forceinline__ reference operator*() const
      {
          value_type retval;
          retval.value = itr[offset];
          retval.key = offset;
          return retval;
      }
  
      /// Addition
      template <typename Distance>
      __host__ __device__ __forceinline__ self_type operator+(Distance n) const
      {
          self_type retval(itr, offset + n);
          return retval;
      }
  
      /// Addition assignment
      template <typename Distance>
      __host__ __device__ __forceinline__ self_type& operator+=(Distance n)
      {
          offset += n;
          return *this;
      }
  
      /// Subtraction
      template <typename Distance>
      __host__ __device__ __forceinline__ self_type operator-(Distance n) const
      {
          self_type retval(itr, offset - n);
          return retval;
      }
  
      /// Subtraction assignment
      template <typename Distance>
      __host__ __device__ __forceinline__ self_type& operator-=(Distance n)
      {
          offset -= n;
          return *this;
      }
  
      /// Distance
      __host__ __device__ __forceinline__ difference_type operator-(self_type other) const
      {
          return offset - other.offset;
      }
  
      /// Array subscript
      template <typename Distance>
      __host__ __device__ __forceinline__ reference operator[](Distance n) const
      {
          self_type offset = (*this) + n;
          return *offset;
      }
  
      /// Structure dereference
      __host__ __device__ __forceinline__ pointer operator->()
      {
          return &(*(*this));
      }
  
      /// Equal to
      __host__ __device__ __forceinline__ bool operator==(const self_type& rhs)
      {
          return ((itr == rhs.itr) && (offset == rhs.offset));
      }
  
      /// Not equal to
      __host__ __device__ __forceinline__ bool operator!=(const self_type& rhs)
      {
          return ((itr != rhs.itr) || (offset != rhs.offset));
      }
  
      /// Normalize
      __host__ __device__ __forceinline__ void normalize()
      {
          itr += offset;
          offset = 0;
      }
  
      /// ostream operator
      friend std::ostream& operator<<(std::ostream& os, const self_type& /*itr*/)
      {
          return os;
      }
  };
  
  
  
  /** @} */       // end group UtilIterator
  
  }               // CUB namespace
  CUB_NS_POSTFIX  // Optional outer namespace(s)