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/*! \file
    \brief Templates implementing loading of convolution tiles mapped to GEMM A (output gradient tile) 
    matrix from memory.

    This iterator assumes TensorNDHWC layout of tensors in Global Memory.

    The iterator is specialized for each of the three convolution operators: forward propagation (Fprop),
    backward data gradient (Dgrad), and backward weight gradient (Wgrad).
*/

#pragma once

#include "cutlass/cutlass.h"
#include "cutlass/array.h"
#include "cutlass/coord.h"
#include "cutlass/predicate_vector.h"
#include "cutlass/tensor_ref.h"
#include "cutlass/tensor_view.h"
#include "cutlass/layout/pitch_linear.h"
#include "cutlass/layout/tensor.h"
#include "cutlass/layout/matrix.h"
#include "cutlass/conv/convolution.h"
#include "cutlass/conv/conv3d_problem_size.h"

/////////////////////////////////////////////////////////////////////////////////////////////////

namespace cutlass {
namespace conv {
namespace threadblock {

/////////////////////////////////////////////////////////////////////////////////////////////////

template <
  typename Shape_,
  typename Element_,
  typename ThreadMap_
>
class Conv3dWgradOutputGradientTileAccessIteratorAnalytic {
public:

  //
  // Types
  //
  using Shape = Shape_;
  using Element = Element_;
  using Layout = layout::TensorNDHWC;
  using ThreadMap = ThreadMap_;
  using AccessType = AlignedArray<Element, ThreadMap::kElementsPerAccess>;
  using TensorRef = cutlass::TensorRef<Element, Layout>;
  using TensorCoord = typename Layout::TensorCoord;
  using Index = typename Layout::Index;
  using LongIndex = typename Layout::LongIndex;
  static IteratorAlgorithm const kIteratorAlgorithm = conv::IteratorAlgorithm::kAnalytic;
  static StrideSupport const kStrideSupport = conv::StrideSupport::kStrided;
  static int const kConvDim = 3;
  using ConvProblemSize = typename conv::Conv3dProblemSize;
  static int const kAccessesPerVector = 1;
  static_assert(sizeof_bits<Element>::value >= 8,
    "WGRAD requires elements of size 8b or greater.");

  //
  // Parameters structure
  //

  struct Params {

    Layout layout;

    //
    // Methods
    //

    CUTLASS_HOST_DEVICE
    Params() { }

    CUTLASS_HOST_DEVICE
    Params(
      Conv3dProblemSize const &problem_size, 
      Layout const &layout
    ): layout(layout) {

    }
  };

private:

  Params const &params_;
  Conv3dProblemSize const &problem_size_;
  LongIndex iteration_contiguous_;
  LongIndex iteration_strided_;
  char const *pointer_;
    
  int filter_k_[ThreadMap::Iterations::kContiguous];

  int offset_nzpq_[ThreadMap::Iterations::kStrided];

public:

  CUTLASS_HOST_DEVICE
  Conv3dWgradOutputGradientTileAccessIteratorAnalytic(
    Params const &params, 
    Conv3dProblemSize const &problem_size,
    Element const *ptr,
    int thread_idx,
    MatrixCoord const &threadblock_offset = MatrixCoord()
  ):
    params_(params), 
    problem_size_(problem_size), 
    pointer_(reinterpret_cast<char const *>(ptr)) {


    layout::PitchLinearCoord thread_coord = ThreadMap::initial_offset(thread_idx);
    
    // initialize filter_k for every contiguous iteration
    CUTLASS_PRAGMA_UNROLL
    for (int c = 0; c < ThreadMap::Iterations::kContiguous; ++c) {
      filter_k_[c] = threadblock_offset.row() + thread_coord.contiguous() 
                        + c * ThreadMap::Delta::kContiguous;
    }

    // initialize n, p, q offset for every strided iteration
    CUTLASS_PRAGMA_UNROLL
    for (int s = 0; s < ThreadMap::Iterations::kStrided; ++s) {
      offset_nzpq_[s] = threadblock_offset.column() + thread_coord.strided() 
                      + s * ThreadMap::Delta::kStrided;  
      
    }
  }

  CUTLASS_HOST_DEVICE
  static Params getParams(Conv3dProblemSize const &problem_size, Layout const &layout) {
    return Params(problem_size, layout);
  }

  /// Overrides the internal iteration index
  CUTLASS_HOST_DEVICE
  void set_iteration_index(Index index) {
    iteration_contiguous_ = index % ThreadMap::Iterations::kContiguous;
    iteration_strided_ = index / ThreadMap::Iterations::kContiguous;
  }

  /// Adds a pointer offset in units of Element
  CUTLASS_HOST_DEVICE
  void add_pointer_offset(LongIndex pointer_offset) {
    pointer_ += pointer_offset * sizeof_bits<Element>::value / 8;
  }

  CUTLASS_HOST_DEVICE
  void advance() {
    // moves to the next GEMM-K offset (offset_nzpq_) in GEMM-A by a CTA-K tile
    CUTLASS_PRAGMA_UNROLL
    for (int s = 0; s < ThreadMap::Iterations::kStrided; ++s) {
      offset_nzpq_[s] += Shape::kColumn * problem_size_.split_k_slices;
    }
  }

  /// Returns the coordinate in the output gradient tensor Dy that is currently pointed to
  /// by the iterator.
  CUTLASS_HOST_DEVICE
  TensorCoord at() const {

    int nzpq = offset_nzpq_[iteration_strided_];

    int n = nzpq / (problem_size_.Z * problem_size_.P * problem_size_.Q);
    int residual = nzpq % (problem_size_.Z * problem_size_.P * problem_size_.Q);

    int z = residual / (problem_size_.P * problem_size_.Q);
    residual = residual % (problem_size_.P * problem_size_.Q);

    int p = residual / problem_size_.Q;
    int q = residual % problem_size_.Q;

    return TensorCoord(n, z, p, q, filter_k_[iteration_contiguous_]);
  }


  /// Returns true if the current coordinate is within the output gradient tensor Dy
  CUTLASS_HOST_DEVICE
  bool valid() const {
    TensorCoord coord = at();

    return coord.n() < problem_size_.N &&
      coord.d() < problem_size_.Z &&
      coord.h() < problem_size_.P &&
      coord.w() < problem_size_.Q &&
      coord.c() < problem_size_.K;
  }

  /// Returns a pointer to the vector starting at the current coordinate
  CUTLASS_HOST_DEVICE
  AccessType const *get() const {

    TensorCoord coord = at();
    LongIndex offset = params_.layout(coord);

    return reinterpret_cast<AccessType const *>(pointer_ + offset * sizeof_bits<Element>::value / 8);
  }

  /// Increments to the next memory access
  CUTLASS_HOST_DEVICE
  Conv3dWgradOutputGradientTileAccessIteratorAnalytic &operator++() {
    ++iteration_contiguous_;
    if (iteration_contiguous_ < ThreadMap::Iterations::kContiguous) {
      return *this;
    }
    iteration_contiguous_ = 0;
    ++iteration_strided_;
    if (iteration_strided_ < ThreadMap::Iterations::kStrided) {
      return *this;
    }
    iteration_strided_ = 0;
 
    return *this;
  }

  /// Determines whether the Implicit GEMM can execute the given problem.
  CUTLASS_HOST_DEVICE
  static Status can_implement(Conv3dProblemSize const &problem_size) {

    // check alignment constraint on iterator's contiguous dimension
    if (problem_size.K % (128/sizeof_bits<Element>::value)) {
      return Status::kErrorInvalidProblem;
    }

    return Status::kSuccess;
  }

};
/////////////////////////////////////////////////////////////////////////////////////////////////

} // namespace threadblock
} // namespace conv
} // namespace cutlass

/////////////////////////////////////////////////////////////////////////////////////////////////


