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// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
#include "cpu/vision.h"
// implementation taken from Caffe2
template <typename T>
struct PreCalc {
int pos1;
int pos2;
int pos3;
int pos4;
T w1;
T w2;
T w3;
T w4;
};
template <typename T>
void pre_calc_for_bilinear_interpolate(
const int height,
const int width,
const int pooled_height,
const int pooled_width,
const int iy_upper,
const int ix_upper,
T roi_start_h,
T roi_start_w,
T bin_size_h,
T bin_size_w,
int roi_bin_grid_h,
int roi_bin_grid_w,
std::vector<PreCalc<T>>& pre_calc) {
int pre_calc_index = 0;
for (int ph = 0; ph < pooled_height; ph++) {
for (int pw = 0; pw < pooled_width; pw++) {
for (int iy = 0; iy < iy_upper; iy++) {
const T yy = roi_start_h + ph * bin_size_h +
static_cast<T>(iy + .5f) * bin_size_h /
static_cast<T>(roi_bin_grid_h); // e.g., 0.5, 1.5
for (int ix = 0; ix < ix_upper; ix++) {
const T xx = roi_start_w + pw * bin_size_w +
static_cast<T>(ix + .5f) * bin_size_w /
static_cast<T>(roi_bin_grid_w);
T x = xx;
T y = yy;
// deal with: inverse elements are out of feature map boundary
if (y < -1.0 || y > height || x < -1.0 || x > width) {
// empty
PreCalc<T> pc;
pc.pos1 = 0;
pc.pos2 = 0;
pc.pos3 = 0;
pc.pos4 = 0;
pc.w1 = 0;
pc.w2 = 0;
pc.w3 = 0;
pc.w4 = 0;
pre_calc[pre_calc_index] = pc;
pre_calc_index += 1;
continue;
}
if (y <= 0) {
y = 0;
}
if (x <= 0) {
x = 0;
}
int y_low = (int)y;
int x_low = (int)x;
int y_high;
int x_high;
if (y_low >= height - 1) {
y_high = y_low = height - 1;
y = (T)y_low;
} else {
y_high = y_low + 1;
}
if (x_low >= width - 1) {
x_high = x_low = width - 1;
x = (T)x_low;
} else {
x_high = x_low + 1;
}
T ly = y - y_low;
T lx = x - x_low;
T hy = 1. - ly, hx = 1. - lx;
T w1 = hy * hx, w2 = hy * lx, w3 = ly * hx, w4 = ly * lx;
// save weights and indeces
PreCalc<T> pc;
pc.pos1 = y_low * width + x_low;
pc.pos2 = y_low * width + x_high;
pc.pos3 = y_high * width + x_low;
pc.pos4 = y_high * width + x_high;
pc.w1 = w1;
pc.w2 = w2;
pc.w3 = w3;
pc.w4 = w4;
pre_calc[pre_calc_index] = pc;
pre_calc_index += 1;
}
}
}
}
}
template <typename T>
void ROIAlignForward_cpu_kernel(
const int nthreads,
const T* bottom_data,
const T& spatial_scale,
const int channels,
const int height,
const int width,
const int pooled_height,
const int pooled_width,
const int sampling_ratio,
const T* bottom_rois,
//int roi_cols,
T* top_data) {
//AT_ASSERT(roi_cols == 4 || roi_cols == 5);
int roi_cols = 5;
int n_rois = nthreads / channels / pooled_width / pooled_height;
// (n, c, ph, pw) is an element in the pooled output
// can be parallelized using omp
// #pragma omp parallel for num_threads(32)
for (int n = 0; n < n_rois; n++) {
int index_n = n * channels * pooled_width * pooled_height;
// roi could have 4 or 5 columns
const T* offset_bottom_rois = bottom_rois + n * roi_cols;
int roi_batch_ind = 0;
if (roi_cols == 5) {
roi_batch_ind = offset_bottom_rois[0];
offset_bottom_rois++;
}
// Do not using rounding; this implementation detail is critical
T roi_start_w = offset_bottom_rois[0] * spatial_scale;
T roi_start_h = offset_bottom_rois[1] * spatial_scale;
T roi_end_w = offset_bottom_rois[2] * spatial_scale;
T roi_end_h = offset_bottom_rois[3] * spatial_scale;
// T roi_start_w = round(offset_bottom_rois[0] * spatial_scale);
// T roi_start_h = round(offset_bottom_rois[1] * spatial_scale);
// T roi_end_w = round(offset_bottom_rois[2] * spatial_scale);
// T roi_end_h = round(offset_bottom_rois[3] * spatial_scale);
// Force malformed ROIs to be 1x1
T roi_width = std::max(roi_end_w - roi_start_w, (T)1.);
T roi_height = std::max(roi_end_h - roi_start_h, (T)1.);
T bin_size_h = static_cast<T>(roi_height) / static_cast<T>(pooled_height);
T bin_size_w = static_cast<T>(roi_width) / static_cast<T>(pooled_width);
// We use roi_bin_grid to sample the grid and mimic integral
int roi_bin_grid_h = (sampling_ratio > 0)
? sampling_ratio
: ceil(roi_height / pooled_height); // e.g., = 2
int roi_bin_grid_w =
(sampling_ratio > 0) ? sampling_ratio : ceil(roi_width / pooled_width);
// We do average (integral) pooling inside a bin
const T count = roi_bin_grid_h * roi_bin_grid_w; // e.g. = 4
// we want to precalculate indeces and weights shared by all chanels,
// this is the key point of optimiation
std::vector<PreCalc<T>> pre_calc(
roi_bin_grid_h * roi_bin_grid_w * pooled_width * pooled_height);
pre_calc_for_bilinear_interpolate(
height,
width,
pooled_height,
pooled_width,
roi_bin_grid_h,
roi_bin_grid_w,
roi_start_h,
roi_start_w,
bin_size_h,
bin_size_w,
roi_bin_grid_h,
roi_bin_grid_w,
pre_calc);
for (int c = 0; c < channels; c++) {
int index_n_c = index_n + c * pooled_width * pooled_height;
const T* offset_bottom_data =
bottom_data + (roi_batch_ind * channels + c) * height * width;
int pre_calc_index = 0;
for (int ph = 0; ph < pooled_height; ph++) {
for (int pw = 0; pw < pooled_width; pw++) {
int index = index_n_c + ph * pooled_width + pw;
T output_val = 0.;
for (int iy = 0; iy < roi_bin_grid_h; iy++) {
for (int ix = 0; ix < roi_bin_grid_w; ix++) {
PreCalc<T> pc = pre_calc[pre_calc_index];
output_val += pc.w1 * offset_bottom_data[pc.pos1] +
pc.w2 * offset_bottom_data[pc.pos2] +
pc.w3 * offset_bottom_data[pc.pos3] +
pc.w4 * offset_bottom_data[pc.pos4];
pre_calc_index += 1;
}
}
output_val /= count;
top_data[index] = output_val;
} // for pw
} // for ph
} // for c
} // for n
}
at::Tensor ROIAlign_forward_cpu(const at::Tensor& input,
const at::Tensor& rois,
const float spatial_scale,
const int pooled_height,
const int pooled_width,
const int sampling_ratio) {
AT_ASSERTM(!input.device().is_cuda(), "input must be a CPU tensor");
AT_ASSERTM(!rois.device().is_cuda(), "rois must be a CPU tensor");
auto num_rois = rois.size(0);
auto channels = input.size(1);
auto height = input.size(2);
auto width = input.size(3);
auto output = at::empty({num_rois, channels, pooled_height, pooled_width}, input.options());
auto output_size = num_rois * pooled_height * pooled_width * channels;
if (output.numel() == 0) {
return output;
}
AT_DISPATCH_FLOATING_TYPES(input.scalar_type(), "ROIAlign_forward", [&] {
ROIAlignForward_cpu_kernel<scalar_t>(
output_size,
input.data_ptr<scalar_t>(),
spatial_scale,
channels,
height,
width,
pooled_height,
pooled_width,
sampling_ratio,
rois.data_ptr<scalar_t>(),
output.data_ptr<scalar_t>());
});
return output;
}
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