TensorTransformations.cpp

#include <ATen/native/TensorTransformations.h>
#include <ATen/native/IndexKernel.h>  // for flip_stub

#include <ATen/NativeFunctions.h>
#include <ATen/Parallel.h>
#include <ATen/WrapDimUtilsMulti.h>
#include <ATen/core/DimVector.h>
#include <c10/util/Exception.h>
#include <c10/util/irange.h>

#include <algorithm>
#include <vector>

namespace at {
namespace native {

Tensor flip(const Tensor& self, IntArrayRef dims) {
  const int64_t total_dims = self.dim();
  // It wraps the dims and checks that there are no repeated dims
  auto flip_dims_b = at::dim_list_to_bitset(dims, total_dims);

  Tensor out_tensor = at::empty_like(self, MemoryFormat::Preserve);

  // Count dimensions in which we need to do work
  int n = 0;
  auto strides = DimVector(self.strides());
  for (const auto i : c10::irange(total_dims)) {
    if(flip_dims_b[i] && self.size(i) > 1 && self.stride(i) != 0) {
      n++;
      strides[i] = 0;
    }
  }

  // Nothing to do, we return fast
  if (n == 0 || self.numel() <=1) {
    out_tensor.copy_(self);
    return out_tensor;
  }

  //create dummy output with 0 strides at flipped dimension, to prevent tensorIterator from coalescing flipped dims
  const auto restrided_self = self.as_strided(self.sizes(), strides);
  auto iter = TensorIteratorConfig()
    .set_check_mem_overlap(false)
    .check_all_same_dtype(false)
    .declare_static_dtype_and_device(self.scalar_type(), self.device())
    .add_output(out_tensor)
    .add_input(self)
    .add_input(restrided_self)
    .build();

  auto* data = reinterpret_cast<char*>(iter.data_ptr(0));
  const auto sizes = iter.shape();
  // This is a SmallVector of _signed_ ints
  auto strides_bytes = DimVector(iter.strides(0));
  const auto strides_self = iter.strides(1);
  const auto strides_dummy = iter.strides(2);

  // To understand this transformation, think of a 3D cube.
  //   - The data ptr points to the lower-left most vertex of the cube
  //   - The strides tell us how to move in each dimension,
  //     that is, data + stride[i] advances one element in the dimension i
  // To flip a dimension:
  //   - We move the pointer to the opposite vertex of the cube
  //   - We iterate in the opposite direction (invert the strides)

  for (const auto i : c10::irange(iter.ndim())) {
    // We know that an dimension has a zero stride and self[i] does not, as we defined above
    // Note that it may be the case that strides_dummy[i] = 0 not because we set it, but because
    // strides_self[i] == 0. We do not want to do anything there
    if (strides_dummy[i] == 0 && strides_self[i] != 0) {
      data += strides_bytes[i] * (sizes[i]-1);
      strides_bytes[i] *= -1;
    }
  }
  iter._unsafe_set_arg_strides(0, strides_bytes);
  iter._unsafe_set_arg_data(0, reinterpret_cast<void*>(data));

  flip_stub(iter.device_type(), iter, self.is_quantized());

  return out_tensor;
}

Tensor roll_cpu(const Tensor& self, IntArrayRef shifts, IntArrayRef dims) {
  if (dims.size() != 1 || shifts.size() != 1) {
    return roll_common(self, shifts, dims);
  }
  // avoid a div zero error below.
  if (self.numel() == 0) {
    return self.clone(at::MemoryFormat::Preserve);
  }
  int64_t dim = dims[0];
  int64_t size = self.size(dim);
  int64_t start = (size - shifts[0]) % size;
  // Behavior of % is different in C++ vs Python for negative numbers. This
  // corrects the difference.
  if (start < 0) {
    start = start + size;
  }
  auto t0 = self.narrow(dim, start, size-start);
  auto t1 = self.narrow(dim, 0, start);
  return at::cat({t0, t1}, dim);
}

Tensor rot90(const Tensor& self, int64_t k, IntArrayRef dims) {
  const int64_t total_dims = self.dim(), total_rot_dims = dims.size();

  TORCH_CHECK(total_rot_dims == 2,
    "expected total rotation dims == 2, but got dims = ", total_rot_dims);

  TORCH_CHECK(total_dims >= 2,
    "expected total dims >= 2, but got total dims = ", total_dims);

  TORCH_CHECK(dims[0] != dims[1] && std::abs(dims[0] - dims[1]) != total_dims,
    "expected rotation dims to be different, but got dim0 = ", dims[0],
    " and dim1 = ", dims[1]);

  // check range of dims
  TORCH_CHECK(dims[0] < total_dims && dims[0] >= -total_dims,
    "Rotation dim0 out of range, dim0 = ", dims[0]);

  TORCH_CHECK(dims[1] < total_dims && dims[1] >= -total_dims,
    "Rotation dim1 out of range, dim1 = ", dims[1]);

  // handle modulo with negative k
  k = (4 + (k % 4)) % 4;

  switch(k) {
    case 1:
      return self.flip({dims[1]}).transpose_(dims[0], dims[1]);
    case 2:
      return self.flip(dims);
    case 3:
      return self.flip({dims[0]}).transpose_(dims[0], dims[1]);
    default:
      return self.clone(at::MemoryFormat::Contiguous);
  }
}

Tensor fliplr(const Tensor& self) {
  TORCH_CHECK(self.dim() >= 2, "Input must be >= 2-d.");

  return self.flip({1});
}

Tensor flipud(const Tensor& self) {
  TORCH_CHECK(self.dim() >= 1, "Input must be >= 1-d.");

  return self.flip({0});
}

Tensor atleast_1d(const Tensor& self) {
  switch (self.dim()) {
    case 0:
      return self.reshape({1});
    default:
      return self;
  }
}

std::vector<Tensor> atleast_1d(TensorList tensors) {
  std::vector<Tensor> result(tensors.size());
  auto transform_lambda = [](const Tensor& input) -> Tensor {
    return at::native::atleast_1d(input);
  };
  std::transform(tensors.cbegin(), tensors.cend(), result.begin(), transform_lambda);
  return result;
}

Tensor atleast_2d(const Tensor& self) {
  switch (self.dim()) {
    case 0:
      return self.reshape({1, 1});
    case 1: {
      return self.unsqueeze(0);
    }
    default:
      return self;
  }
}

std::vector<Tensor> atleast_2d(TensorList tensors) {
  std::vector<Tensor> result(tensors.size());
  auto transform_lambda = [](const Tensor& input) -> Tensor {
    return at::native::atleast_2d(input);
  };
  std::transform(tensors.cbegin(), tensors.cend(), result.begin(), transform_lambda);
  return result;
}

Tensor atleast_3d(const Tensor& self) {
  switch (self.dim()) {
    case 0:
      return self.reshape({1, 1, 1});
    case 1: {
      return self.unsqueeze(0).unsqueeze(-1);
    }
    case 2: {
      return self.unsqueeze(-1);
    }
    default:
      return self;
  }
}

std::vector<Tensor> atleast_3d(TensorList tensors) {
  std::vector<Tensor> result(tensors.size());
  auto transform_lambda = [](const Tensor& input) -> Tensor {
    return at::native::atleast_3d(input);
  };
  std::transform(tensors.cbegin(), tensors.cend(), result.begin(), transform_lambda);
  return result;
}

DEFINE_DISPATCH(flip_stub);

}} // namespace at::native