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 * Copyright (c) 2011-2018, NVIDIA CORPORATION.  All rights reserved.
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 *       notice, this list of conditions and the following disclaimer.
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 *       names of its contributors may be used to endorse or promote products
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/**
 * @file
 * Random-access iterator types
 */

#pragma once

#include <cub/config.cuh>

#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 <cub/thread/thread_load.cuh>
#include <cub/thread/thread_store.cuh>

#include <iostream>
#include <iterator>

#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

CUB_NAMESPACE_BEGIN

/**
 * @brief A random-access input generator for dereferencing a sequence of homogeneous values
 *
 * @par Overview
 * - Read references to a ConstantInputIteratorTiterator always return the supplied constant
 *   of type @p ValueType.
 * - Can be used with any data type.
 * - Can be constructed, manipulated, dereferenced, and exchanged within and between host and device
 *   functions.
 * - Compatible with Thrust API v1.7 or newer.
 *
 * @par Snippet
 * The code snippet below illustrates the use of @p ConstantInputIteratorTto
 * dereference a sequence of homogeneous doubles.
 * @par
 * @code
 * #include <cub/cub.cuh>   // or equivalently <cub/iterator/constant_input_iterator.cuh>
 *
 * cub::ConstantInputIterator<double> itr(5.0);
 *
 * printf("%f\n", itr[0]);      // 5.0
 * printf("%f\n", itr[1]);      // 5.0
 * printf("%f\n", itr[2]);      // 5.0
 * printf("%f\n", itr[50]);     // 5.0
 *
 * @endcode
 *
 * @tparam ValueType
 *   The value type of this iterator
 *
 * @tparam OffsetT
 *   The difference type of this iterator (Default: @p ptrdiff_t)
 */
template <typename ValueType, typename OffsetT = ptrdiff_t>
class ConstantInputIterator
{
public:
  // Required iterator traits

  /// My own type
  using self_type = ConstantInputIterator;

  /// Type to express the result of subtracting one iterator from another
  using difference_type = OffsetT;

  /// The type of the element the iterator can point to
  using value_type = ValueType;

  /// The type of a pointer to an element the iterator can point to
  using pointer = ValueType*;

  /// The type of a reference to an element the iterator can point to
  using reference = ValueType;

#if (THRUST_VERSION >= 100700)
  // Use Thrust's iterator categories so we can use these iterators in Thrust 1.7 (or newer) methods

  /// The iterator category
  using iterator_category = typename THRUST_NS_QUALIFIER::detail::iterator_facade_category<
    THRUST_NS_QUALIFIER::any_system_tag,
    THRUST_NS_QUALIFIER::random_access_traversal_tag,
    value_type,
    reference>::type;
#else
  /// The iterator category
  using iterator_category = std::random_access_iterator_tag;
#endif // THRUST_VERSION

private:
  ValueType val;
  OffsetT offset;
#ifdef _WIN32
  // Workaround for win32 parameter-passing bug (ulonglong2 argmin DeviceReduce)
  OffsetT pad[CUB_MAX(1, (16 / sizeof(OffsetT) - 1))];
#endif

public:
  /**
   * @param val
   *   Starting value for the iterator instance to report
   *
   * @param offset
   *   Base offset
   */
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE ConstantInputIterator(ValueType val, OffsetT offset = 0)
      : val(val)
      , offset(offset)
  {}

  /// Postfix increment
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE self_type operator++(int)
  {
    self_type retval = *this;
    offset++;
    return retval;
  }

  /// Prefix increment
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE self_type operator++()
  {
    offset++;
    return *this;
  }

  /// Indirection
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE reference operator*() const
  {
    return val;
  }

  /// Addition
  template <typename Distance>
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE self_type operator+(Distance n) const
  {
    self_type retval(val, offset + n);
    return retval;
  }

  /// Addition assignment
  template <typename Distance>
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE self_type& operator+=(Distance n)
  {
    offset += n;
    return *this;
  }

  /// Subtraction
  template <typename Distance>
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE self_type operator-(Distance n) const
  {
    self_type retval(val, offset - n);
    return retval;
  }

  /// Subtraction assignment
  template <typename Distance>
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE self_type& operator-=(Distance n)
  {
    offset -= n;
    return *this;
  }

  /// Distance
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE difference_type operator-(self_type other) const
  {
    return offset - other.offset;
  }

  /// Array subscript
  template <typename Distance>
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE reference operator[](Distance /*n*/) const
  {
    return val;
  }

  /// Structure dereference
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE pointer operator->()
  {
    return &val;
  }

  /// Equal to
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE bool operator==(const self_type& rhs) const
  {
    return (offset == rhs.offset) && ((val == rhs.val));
  }

  /// Not equal to
  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE bool operator!=(const self_type& rhs) const
  {
    return (offset != rhs.offset) || (val != rhs.val);
  }

  /// ostream operator
  friend std::ostream& operator<<(std::ostream& os, const self_type& itr)
  {
    os << "[" << itr.val << "," << itr.offset << "]";
    return os;
  }
};

CUB_NAMESPACE_END