/******************************************************************************
 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
 * Copyright (c) 2011-2018, NVIDIA CORPORATION.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * 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.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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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

#if !defined(_CCCL_COMPILER_NVRTC)
#  include <iostream>
#  include <iterator>
#else
#  include <cuda/std/iterator>
#endif

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


CUB_NAMESPACE_BEGIN

/**
 * @brief A random-access input wrapper for dereferencing array values using a PTX cache load
 *        modifier.
 *
 * @par Overview
 * - CacheModifiedInputIterator is a random-access input iterator that wraps a native
 *   device pointer of type <tt>ValueType*</tt>. @p ValueType references are
 *   made by reading @p ValueType values through loads modified by @p MODIFIER.
 * - Can be used to load any data type from memory using PTX cache load modifiers (e.g., "LOAD_LDG",
 *   "LOAD_CG", "LOAD_CA", "LOAD_CS", "LOAD_CV", etc.).
 * - Can be constructed, manipulated, and exchanged within and between host and device
 *   functions, but can only be dereferenced within device functions.
 * - Compatible with Thrust API v1.7 or newer.
 *
 * @par Snippet
 * The code snippet below illustrates the use of @p CacheModifiedInputIterator to
 * dereference a device array of double using the "ldg" PTX load modifier
 * (i.e., load values through texture cache).
 * @par
 * @code
 * #include <cub/cub.cuh>   // or equivalently <cub/iterator/cache_modified_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::CacheModifiedInputIterator<cub::LOAD_LDG, double> itr(d_in);
 *
 * // Within device code:
 * printf("%f\n", itr[0]);  // 8.0
 * printf("%f\n", itr[1]);  // 6.0
 * printf("%f\n", itr[6]);  // 9.0
 *
 * @endcode
 *
 * @tparam CacheLoadModifier
 *   The cub::CacheLoadModifier to use when accessing data
 *
 * @tparam ValueType
 *   The value type of this iterator
 *
 * @tparam OffsetT
 *   The difference type of this iterator (Default: @p ptrdiff_t)
 */
template <
    CacheLoadModifier   MODIFIER,
    typename            ValueType,
    typename            OffsetT = ptrdiff_t>
class CacheModifiedInputIterator
{
public:

    // Required iterator traits

    /// My own type
    typedef CacheModifiedInputIterator self_type;

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

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

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

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

#if !defined(_CCCL_COMPILER_NVRTC)
#  if (THRUST_VERSION >= 100700)
    // Use Thrust's iterator categories so we can use these iterators in Thrust 1.7 (or newer) methods
    using iterator_category = typename THRUST_NS_QUALIFIER::detail::iterator_facade_category<
      THRUST_NS_QUALIFIER::device_system_tag,
      THRUST_NS_QUALIFIER::random_access_traversal_tag,
      value_type,
      reference>::type;
#  else // THRUST_VERSION < 100700
    using iterator_category = std::random_access_iterator_tag;
#  endif // THRUST_VERSION
#else // defined(_CCCL_COMPILER_NVRTC)
    using iterator_category = ::cuda::std::random_access_iterator_tag;
#endif // defined(_CCCL_COMPILER_NVRTC)

  public:

    /// Wrapped native pointer
    ValueType* ptr;

    /// Constructor
    template <typename QualifiedValueType>
    _CCCL_HOST_DEVICE _CCCL_FORCEINLINE CacheModifiedInputIterator(
        QualifiedValueType* ptr)     ///< Native pointer to wrap
    :
        ptr(const_cast<typename ::cuda::std::remove_cv<QualifiedValueType>::type *>(ptr))
    {}

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

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

    /// Indirection
    _CCCL_DEVICE _CCCL_FORCEINLINE reference operator*() const
    {
        return ThreadLoad<MODIFIER>(ptr);
    }

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

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

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

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

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

    /// Array subscript
    template <typename Distance>
    _CCCL_DEVICE _CCCL_FORCEINLINE reference operator[](Distance n) const
    {
        return ThreadLoad<MODIFIER>(ptr + n);
    }

    /// Structure dereference
    _CCCL_DEVICE _CCCL_FORCEINLINE pointer operator->()
    {
        return &ThreadLoad<MODIFIER>(ptr);
    }

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

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

    /// ostream operator
#if !defined(_CCCL_COMPILER_NVRTC)
    friend std::ostream& operator<<(std::ostream& os, const self_type& /*itr*/)
    {
        return os;
    }
#endif
};

CUB_NAMESPACE_END
