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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 TensorNHWC 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 "hytlass/hytlass.h"
#include "hytlass/array.h"
#include "hytlass/coord.h"
#include "hytlass/functional.h"
#include "hytlass/predicate_vector.h"
#include "hytlass/tensor_ref.h"
#include "hytlass/tensor_view.h"
#include "hytlass/layout/pitch_linear.h"
#include "hytlass/layout/tensor.h"
#include "hytlass/layout/matrix.h"
#include "hytlass/conv/convolution.h"
#include "hytlass/conv/conv2d_problem_size.h"
#include "hytlass/conv/threadblock/conv2d_params.h"

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

namespace hytlass {
namespace conv {
namespace threadblock {

/////////////////////////////////////////////////////////////////////////////////////////////////
template <
  typename Shape_,
  typename Element_,
  typename ThreadMap_,
  conv::StrideSupport StrideSupport_ = conv::StrideSupport::kStrided,
  typename AccessType_ = hytlass::AlignedArray<Element_, ThreadMap_::kElementsPerAccess>
>
class Conv2dDgradOutputGradientTileAccessIteratorAnalytic;
/////////////////////////////////////////////////////////////////////////////////////////////////

// Conv2dDgradOutputGradientTileAccessIteratorAnalytic strided dgrad needs special handling using
// unscaled coordinations
template <
  typename Shape_,
  typename Element_,
  typename ThreadMap_,
  typename AccessType_
>
class Conv2dDgradOutputGradientTileAccessIteratorAnalytic <
  Shape_,
  Element_,
  ThreadMap_,
  conv::StrideSupport::kStrided,
  AccessType_
> {
public:

  //
  // Types
  //
  using Shape = Shape_;
  using Element = Element_;
  using Layout = layout::TensorNHWC;
  using ThreadMap = ThreadMap_;
  using AccessType = AccessType_;
  using TensorRef = hytlass::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 = 2;
  using ConvProblemSize = typename conv::Conv2dProblemSize;
 
  static int const kAccessesPerVector = ThreadMap::kElementsPerAccess / AccessType::kElements;
  
  static_assert(!(ThreadMap::kElementsPerAccess % AccessType::kElements), 
    "Vectors implied by the thread map must be divisible by the access type.");
 
  static_assert(sizeof_bits<Element>::value >= 8,
    "DGRAD requires elements of size 8b or greater.");
 
  //
  // Simpligying assertions
  //

  static_assert(ThreadMap::Iterations::kContiguous == 1,
    "Require Iterations::kContiguous == 1");

  //
  // Parameters structure
  //

  using Params = Conv2dDgradOutputGradientTileAccessIteratorAnalyticParams;

private:

  Params const &params_;
  Conv2dProblemSize const &problem_size_;
  LongIndex iteration_contiguous_;
  LongIndex iteration_strided_;
  LongIndex iteration_vector_;
  char const *pointer_;

  int filter_k_;
  int filter_r_;
  int filter_s_;
  int start_r_;
  int start_s_;

  int offset_n_[ThreadMap::Iterations::kStrided];
  int offset_p_[ThreadMap::Iterations::kStrided];
  int offset_q_[ThreadMap::Iterations::kStrided];

public:

  HYTLASS_HOST_DEVICE
  Conv2dDgradOutputGradientTileAccessIteratorAnalytic(
    Params const &params, 
    Conv2dProblemSize const &problem_size,
    Element const *ptr,
    int thread_idx,
    FastDivmod const &stride_h_divmod, FastDivmod const &stride_w_divmod,
    int start_r, int start_s,
    MatrixCoord const &threadblock_offset = MatrixCoord()     // threadblock offset - units are whole CTA tiles
  ):
    params_(params), 
    problem_size_(problem_size), 
    pointer_(reinterpret_cast<char const *>(ptr)), 
    filter_k_(0),
    filter_r_(start_r),
    filter_s_(start_s),
    start_r_(start_r),
    start_s_(start_s) {

    layout::PitchLinearCoord thread_coord = ThreadMap::initial_offset(thread_idx);

    filter_k_ = threadblock_offset.column() + thread_coord.contiguous();

    int filter_r = filter_r_;
    int filter_s = filter_s_;

    if (problem_size_.mode == Mode::kConvolution) {
      filter_r = (problem_size_.R - 1 - filter_r);
      filter_s = (problem_size_.S - 1 - filter_s);
    }

    // Starting h, w positions for filter position in gemm_k=0
    int start_h, start_w;
    strided_dgrad_starting_coords(
      problem_size_, 
      stride_h_divmod, stride_w_divmod, 
      filter_r, filter_s, 
      start_h, start_w);

    // Effective P and Q for filter position required for remapping NHW rows
    int P = (problem_size_.H - start_h + problem_size_.stride_h - 1) / problem_size_.stride_h;
    int Q = (problem_size_.W - start_w + problem_size_.stride_w - 1) / problem_size_.stride_w;


    HYTLASS_PRAGMA_UNROLL
    for (int s = 0; s < ThreadMap::Iterations::kStrided; ++s) {
      int offset_npq = (threadblock_offset.row() + thread_coord.strided() + s * ThreadMap::Delta::kStrided) % params_.tiled_rows_per_filter;

      // (STEP 1) [reorder NHW rows to start with same filter positions]
      offset_n_[s] = offset_npq / (P * Q);
      int residual = offset_npq % (P * Q);

      int p = (residual / Q);
      int q = (residual % Q);

      int mapped_h = (start_h + p * problem_size_.stride_h);
      int mapped_w = (start_w + q * problem_size_.stride_w);
      
      // Access (p, q) coordinates for Dy tensor and a filter position in gemm_k=0
      // note that (h + pad_h - filter_r) and (w + pad_w - filter_s) are divisible 
      // by stride_h and stride_w
      offset_p_[s] = (mapped_h + problem_size_.pad_h - filter_r) / problem_size_.stride_h;
      offset_q_[s] = (mapped_w + problem_size_.pad_w - filter_s) / problem_size_.stride_w;
    }
  }

  HYTLASS_HOST_DEVICE
  static Params getParams(Conv2dProblemSize const &problem_size, Layout const &layout) {
    return Params(problem_size, 
                  layout,
                  sizeof_bits<Element>::value,
                  {Shape::kRow, Shape::kColumn});
  }

  /// Overrides the internal iteration index
  HYTLASS_HOST_DEVICE
  void set_iteration_index(Index index) {
    iteration_vector_ = index % kAccessesPerVector;
    int residual_access = index / kAccessesPerVector;
    iteration_contiguous_ = residual_access % ThreadMap::Iterations::kContiguous;
    iteration_strided_ = residual_access / ThreadMap::Iterations::kContiguous;
  }

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

  HYTLASS_HOST_DEVICE
  void advance() {

    // Move filter_s by stride_w
    filter_s_ +=  problem_size_.stride_w;
    if (filter_s_ < problem_size_.S) {
      return;
    }

    // Restore filter_s 
    filter_s_ = start_s_;

    // Move filter_r by stride_h
    filter_r_ +=  problem_size_.stride_h;
    if (filter_r_ < problem_size_.R) {
      return;
    }

    // Restore filter_r 
    filter_r_ = start_r_;

    // Move filter_k
    filter_k_ += Shape_::kColumn * problem_size_.split_k_slices;
  }

  /// Returns the coordinate in the output tensor Dy that is currently pointed to
  /// by the iterator.
  HYTLASS_HOST_DEVICE
  TensorCoord at() const {
    int n = offset_n_[iteration_strided_];
    int p = offset_p_[iteration_strided_]; 
    int q = offset_q_[iteration_strided_];
    
    int conv_sign = (problem_size_.mode == Mode::kConvolution ? 1 : -1);

    p += (conv_sign * (filter_r_ / problem_size_.stride_h));
    q += (conv_sign * (filter_s_ / problem_size_.stride_w));

    int k = filter_k_ + iteration_vector_ * AccessType::kElements; 

    return TensorCoord(
      n, 
      p, 
      q, 
      k);
  }


  /// Returns true if the current coordinate is within the output tensor Dy
  HYTLASS_HOST_DEVICE
  bool valid() const {

    TensorCoord coord = at();

    return 
      coord.n() < problem_size_.N &&
      coord.h() >= 0 && coord.h() < problem_size_.P &&
      coord.w() >= 0 && coord.w() < problem_size_.Q &&
      coord.c() < problem_size_.K;
  }

  /// Returns a pointer to the vector starting at the current coordinate
  HYTLASS_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
  HYTLASS_HOST_DEVICE
  Conv2dDgradOutputGradientTileAccessIteratorAnalytic &operator++() {
    ++iteration_vector_;
    if (iteration_vector_ < kAccessesPerVector) {
      return *this;
    }
    iteration_vector_ = 0;

    ++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.
  HYTLASS_HOST_DEVICE
  static Status can_implement(Conv2dProblemSize const &problem_size) {

    // check alignment constraint on iterator's contiguous dimension
    if (problem_size.K % AccessType::kElements) {
      return Status::kErrorInvalidProblem;
    }

    return Status::kSuccess;
  }
};

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

// Conv2dDgradOutputGradientTileAccessIteratorAnalytic for unity strides can be optimized by 
// eliminating modulo arithmetic to compute unscaled coordinates 
template <
  typename Shape_,
  typename Element_,
  typename ThreadMap_,
  typename AccessType_
>
class Conv2dDgradOutputGradientTileAccessIteratorAnalytic < 
  Shape_,
  Element_,
  ThreadMap_,
  conv::StrideSupport::kUnity,
  AccessType_
> {
public:

  //
  // Types
  //
  using Shape = Shape_;
  using Element = Element_;
  using Layout = layout::TensorNHWC;
  using ThreadMap = ThreadMap_;
  using AccessType = AccessType_;
  using TensorRef = hytlass::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::kUnity;
  static int const kConvDim = 2;
  using ConvProblemSize = typename conv::Conv2dProblemSize;
 
  static int const kAccessesPerVector = ThreadMap::kElementsPerAccess / AccessType::kElements;
  
  static_assert(!(ThreadMap::kElementsPerAccess % AccessType::kElements), 
    "Vectors implied by the thread map must be divisible by the access type.");
 
  static_assert(sizeof_bits<Element>::value >= 8,
    "DGRAD requires elements of size 8b or greater.");
 
  //
  // Simpligying assertions
  //

  static_assert(ThreadMap::Iterations::kContiguous == 1,
    "Require Iterations::kContiguous == 1");

  //
  // Parameters structure
  //

  struct Params {

    Layout layout;

    //
    // Methods
    //
    HYTLASS_HOST_DEVICE
    Params() { }

    HYTLASS_HOST_DEVICE
    Params(
      Conv2dProblemSize const &problem_size, 
      Layout const &layout
    ): layout(layout) {

    }
  };

private:

  Params const &params_;
  Conv2dProblemSize const &problem_size_;
  LongIndex iteration_contiguous_;
  LongIndex iteration_strided_;
  LongIndex iteration_vector_;
  char const *pointer_;

  int filter_k_;
  int filter_r_;
  int filter_s_;

  int offset_n_[ThreadMap::Iterations::kStrided];
  int offset_w_[ThreadMap::Iterations::kStrided];
  int offset_h_[ThreadMap::Iterations::kStrided];

public:

  HYTLASS_HOST_DEVICE
  Conv2dDgradOutputGradientTileAccessIteratorAnalytic(
    Params const &params, 
    Conv2dProblemSize const &problem_size,
    Element const *ptr,
    int thread_idx,
    MatrixCoord const &threadblock_offset = MatrixCoord()     // threadblock offset - units are whole CTA tiles
  ):
    params_(params), 
    problem_size_(problem_size), 
    pointer_(reinterpret_cast<char const *>(ptr)), 
    filter_k_(0), 
    filter_r_(0), 
    filter_s_(0) {

    layout::PitchLinearCoord thread_coord = ThreadMap::initial_offset(thread_idx);

    filter_k_ = threadblock_offset.column() + thread_coord.contiguous();

    HYTLASS_PRAGMA_UNROLL
    for (int s = 0; s < ThreadMap::Iterations::kStrided; ++s) {
      int offset_nhw = threadblock_offset.row() + thread_coord.strided() + s * ThreadMap::Delta::kStrided;

      offset_n_[s] = offset_nhw / (problem_size_.H * problem_size_.W);
      int residual = offset_nhw % (problem_size_.H * problem_size_.W);

      offset_h_[s] = residual / problem_size_.W;
      offset_w_[s] = residual % problem_size_.W;
    }
  }

  HYTLASS_HOST_DEVICE
  static Params getParams(Conv2dProblemSize const &problem_size, Layout const &layout) {
    return Params(problem_size, layout);
  }

  /// Overrides the internal iteration index
  HYTLASS_HOST_DEVICE
  void set_iteration_index(Index index) {
    iteration_vector_ = index % kAccessesPerVector;
    int residual_access = index / kAccessesPerVector;
    iteration_contiguous_ = residual_access % ThreadMap::Iterations::kContiguous;
    iteration_strided_ = residual_access / ThreadMap::Iterations::kContiguous;
  }

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

  HYTLASS_HOST_DEVICE
  void advance() {
    // move to the next tile
    ++filter_s_;
    if (filter_s_ < problem_size_.S) {
      return;
    }
    filter_s_  = 0;
    ++filter_r_;
    if (filter_r_ < problem_size_.R) {
      return;
    }
    filter_r_ = 0;

    filter_k_ += Shape_::kColumn * problem_size_.split_k_slices;
  }

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

    int n = offset_n_[iteration_strided_];
    int h = offset_h_[iteration_strided_];
    int w = offset_w_[iteration_strided_];

    int r = filter_r_;
    int s = filter_s_;

    if (problem_size_.mode == Mode::kConvolution) {
      r = (problem_size_.R - 1 - r);
      s = (problem_size_.S - 1 - s);
    }

    int p = (h + problem_size_.pad_h - r * problem_size_.dilation_h) / problem_size_.stride_h;
    int q = (w + problem_size_.pad_w - s * problem_size_.dilation_w) / problem_size_.stride_w;

    int k = filter_k_ + iteration_vector_ * AccessType::kElements;

    return TensorCoord(n, p, q, k);
  }

  /// Returns true if the current coordinate is within the output tensor Dy
  HYTLASS_HOST_DEVICE
  bool valid() const {

    TensorCoord coord = at();

    return coord.n() < problem_size_.N &&
      coord.h() >= 0 && coord.h() < problem_size_.P &&
      coord.w() >= 0 && coord.w() < problem_size_.Q &&
      coord.c() < problem_size_.K;
  }

  /// Returns a pointer to the vector starting at the current coordinate
  HYTLASS_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
  HYTLASS_HOST_DEVICE
  Conv2dDgradOutputGradientTileAccessIteratorAnalytic &operator++() {
    ++iteration_vector_;
    if (iteration_vector_ < kAccessesPerVector) {
      return *this;
    }
    iteration_vector_ = 0;

    ++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.
  HYTLASS_HOST_DEVICE
  static Status can_implement(Conv2dProblemSize const &problem_size) {

    // Conv2dDgradFilterTileAccessIteratorAnalytic unity stride specialization 
    // only supports (stride_h, stride_w) = (1, 1)
    if (problem_size.stride() != MatrixCoord({1, 1})) {
      return Status::kErrorNotSupported;
    }

    // check alignment constraint on iterator's contiguous dimension
    if (problem_size.K % AccessType::kElements) {
      return Status::kErrorInvalidProblem;
    }

    return Status::kSuccess;
  }
  
};

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

} // namespace threadblock
} // namespace conv
} // namespace hytlass

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


