thrust/cub/iterator/constant_input_iterator.cuh

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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 "../config.cuh"

#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 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
    typedef ConstantInputIterator               self_type;              ///< My own type
    typedef OffsetT                             difference_type;        ///< Type to express the result of subtracting one iterator from another
    typedef ValueType                           value_type;             ///< The type of the element the iterator can point to
    typedef ValueType*                          pointer;                ///< The type of a pointer to an element the iterator can point to
    typedef ValueType                           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:

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

public:

    /// Constructor
    __host__ __device__ __forceinline__ ConstantInputIterator(
        ValueType   val,            ///< Starting value for the iterator instance to report
        OffsetT     offset = 0)     ///< Base offset
    :
        val(val),
        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
    {
        return val;
    }

    /// Addition
    template <typename Distance>
    __host__ __device__ __forceinline__ self_type operator+(Distance n) const
    {
        self_type retval(val, 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(val, 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
    {
        return val;
    }

    /// Structure dereference
    __host__ __device__ __forceinline__ pointer operator->()
    {
        return &val;
    }

    /// Equal to
    __host__ __device__ __forceinline__ bool operator==(const self_type& rhs)
    {
        return (offset == rhs.offset) && ((val == rhs.val));
    }

    /// Not equal to
    __host__ __device__ __forceinline__ bool operator!=(const self_type& rhs)
    {
        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;
    }

};


/** @} */       // end group UtilIterator

}               // CUB namespace
CUB_NS_POSTFIX  // Optional outer namespace(s)