// SPDX-FileCopyrightText: Copyright (c) 2011-2022, NVIDIA CORPORATION. All rights reserved.
// SPDX-License-Identifier: BSD-3

//! @file
//! cub::DeviceMemcpy provides device-wide, parallel operations for copying data.

#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/device/dispatch/dispatch_batch_memcpy.cuh>

#include <cuda/std/__type_traits/is_pointer.h>
#include <cuda/std/cstdint>

CUB_NAMESPACE_BEGIN

//! @brief cub::DeviceMemcpy provides device-wide, parallel operations for copying data.
struct DeviceMemcpy
{
  //! @rst
  //! Copies data from a batch of given source buffers to their corresponding destination buffer.
  //!
  //! .. versionadded:: 2.2.0
  //!    First appears in CUDA Toolkit 12.3.
  //!
  //! .. note::
  //!
  //!    If any input buffer aliases memory from any output buffer the behavior is undefined.
  //!    If any output buffer aliases memory of another output buffer the behavior is undefined.
  //!    Input buffers can alias one another.
  //!
  //! Snippet
  //! +++++++
  //!
  //! The code snippet below illustrates usage of DeviceMemcpy::Batched for mutating strings withing
  //! a single string buffer.
  //!
  //! .. code-block:: c++
  //!
  //!    struct GetPtrToStringItem
  //!    {
  //!      __host__ __device__ __forceinline__ void *operator()(uint32_t index)
  //!      {
  //!        return &d_string_data_in[d_string_offsets[index]];
  //!      }
  //!      char *d_string_data_in;
  //!      uint32_t *d_string_offsets;
  //!    };
  //!
  //!    struct GetStringItemSize
  //!    {
  //!      __host__ __device__ __forceinline__ uint32_t operator()(uint32_t index)
  //!      {
  //!        return d_string_offsets[index + 1] - d_string_offsets[index];
  //!      }
  //!      uint32_t *d_string_offsets;
  //!    };
  //!
  //!    uint32_t num_strings = 5;
  //!    char *d_string_data_in;         // e.g., "TomatoesBananasApplesOrangesGrapes"
  //!    char *d_string_data_out;        // e.g., "                ...               "
  //!    uint32_t *d_string_offsets_old; // e.g., [0, 8, 15, 21, 28, 34]
  //!    uint32_t *d_string_offsets_new; // e.g., [0, 6, 13, 19, 26, 34]
  //!    uint32_t *d_gather_index;       // e.g., [2, 1, 4, 3, 0]
  //!
  //!    // Initialize an iterator that returns d_gather_index[i] when the i-th item is dereferenced
  //!    auto gather_iterator = thrust::make_permutation_iterator(thrust::make_counting_iterator(0),
  //!    d_gather_index);
  //!
  //!    // Returns pointers to the input buffer for each string
  //!    auto str_ptrs_in = thrust::make_transform_iterator(gather_iterator,
  //!                                                       GetPtrToStringItem{d_string_data_in,
  //!    d_string_offsets_old});
  //!
  //!    // Returns the string size of the i-th string
  //!    auto str_sizes = thrust::make_transform_iterator(gather_iterator,
  //!    GetStringItemSize{d_string_offsets_old});
  //!
  //!    // Returns pointers to the output buffer for each string
  //!    auto str_ptrs_out = thrust::make_transform_iterator(thrust::make_counting_iterator(0),
  //!                                                        GetPtrToStringItem{d_string_data_out,
  //!    d_string_offsets_new});
  //!
  //!    // Determine temporary device storage requirements
  //!    void *d_temp_storage      = nullptr;
  //!    size_t temp_storage_bytes = 0;
  //!    cub::DeviceMemcpy::Batched(d_temp_storage, temp_storage_bytes, str_ptrs_in, str_ptrs_out,
  //!    str_sizes, num_strings);
  //!
  //!    // Allocate temporary storage
  //!    cudaMalloc(&d_temp_storage, temp_storage_bytes);
  //!
  //!    // Run batched copy algorithm (used to permute strings)
  //!    cub::DeviceMemcpy::Batched(d_temp_storage, temp_storage_bytes, str_ptrs_in, str_ptrs_out,
  //!    str_sizes, num_strings);
  //!
  //!    // d_string_data_out       <-- "ApplesBananasGrapesOrangesTomatoe"
  //!
  //! @endrst
  //!
  //! @tparam InputBufferIt
  //!   **[inferred]** Device-accessible random-access input iterator type providing the pointers to
  //!   the source memory buffers
  //!
  //! @tparam OutputBufferIt
  //!   **[inferred]** Device-accessible random-access input iterator type providing the pointers to
  //!   the destination memory buffers
  //!
  //! @tparam BufferSizeIteratorT
  //!   **[inferred]** Device-accessible random-access input iterator type providing the number of bytes
  //!   to be copied for each pair of buffers
  //!
  //! @param[in] d_temp_storage
  //!   Device-accessible allocation of temporary storage. When `nullptr`, the
  //!   required allocation size is written to `temp_storage_bytes` and no work is done.
  //!
  //! @param[in,out] temp_storage_bytes
  //!   Reference to size in bytes of `d_temp_storage` allocation
  //!
  //! @param[in] input_buffer_it
  //!   Device-accessible iterator providing the pointers to the source memory buffers
  //!
  //! @param[in] output_buffer_it
  //!   Device-accessible iterator providing the pointers to the destination memory buffers
  //!
  //! @param[in] buffer_sizes
  //!   Device-accessible iterator providing the number of bytes to be copied for each pair of buffers
  //!
  //! @param[in] num_buffers
  //!   The total number of buffer pairs
  //!
  //! @param[in] stream
  //!   @rst
  //!   **[optional]** CUDA stream to launch kernels within. Default is stream\ :sub:`0`.
  //!   @endrst
  template <typename InputBufferIt, typename OutputBufferIt, typename BufferSizeIteratorT>
  CUB_RUNTIME_FUNCTION static cudaError_t Batched(
    void* d_temp_storage,
    size_t& temp_storage_bytes,
    InputBufferIt input_buffer_it,
    OutputBufferIt output_buffer_it,
    BufferSizeIteratorT buffer_sizes,
    ::cuda::std::int64_t num_buffers,
    cudaStream_t stream = 0)
  {
    _CCCL_NVTX_RANGE_SCOPE_IF(d_temp_storage, "cub::DeviceMemcpy::Batched");
    static_assert(::cuda::std::is_pointer_v<cub::detail::it_value_t<InputBufferIt>>,
                  "DeviceMemcpy::Batched only supports copying of memory buffers."
                  "Please consider using DeviceCopy::Batched instead.");
    static_assert(::cuda::std::is_pointer_v<cub::detail::it_value_t<OutputBufferIt>>,
                  "DeviceMemcpy::Batched only supports copying of memory buffers."
                  "Please consider using DeviceCopy::Batched instead.");

    // Integer type large enough to hold any offset in [0, num_thread_blocks_launched), where a safe
    // upper bound on num_thread_blocks_launched can be assumed to be given by
    // IDIV_CEIL(num_buffers, 64)
    using BlockOffsetT = uint32_t;

    return detail::
      DispatchBatchMemcpy<InputBufferIt, OutputBufferIt, BufferSizeIteratorT, BlockOffsetT, CopyAlg::Memcpy>::Dispatch(
        d_temp_storage, temp_storage_bytes, input_buffer_it, output_buffer_it, buffer_sizes, num_buffers, stream);
  }
};

CUB_NAMESPACE_END
