area_pixel_compute_source_index Class — pytorch Architecture

Source Code

aten/src/ATen/native/UpSample.h lines 287–313

template <typename scalar_t>
inline scalar_t area_pixel_compute_source_index(
    scalar_t scale,
    int64_t dst_index,
    bool align_corners,
    bool cubic) {
  if (align_corners) {
    return scale * dst_index;
  } else {
    scalar_t src_idx = scale * (dst_index + static_cast<scalar_t>(0.5)) -
        static_cast<scalar_t>(0.5);
    // [Note] Follow Opencv resize logic:
    // We allow negative src_idx here and later will use
    //   dx = src_idx - floorf(src_idx)
    // to compute the "distance"(which affects weights).
    // For linear modes, weight distribution doesn't matter
    // for negative indices as they use 2 pixels to interpolate.
    // For example, [-1, 0], they both use pixel 0 value so it
    // doesn't affect if we bound the src_idx to 0 or not.
    // TODO: Our current linear mode impls use unbound indices
    // where we should and then remove this cubic flag.
    // This matters in cubic mode, as we might need [-1, 0, 1, 2]
    // to interpolate and the weights can be affected.
    return (!cubic && src_idx < static_cast<scalar_t>(0)) ? scalar_t(0)
                                                          : src_idx;
  }
}