added cpu extension

cpu/fps.cpp

+#include <torch/extension.h>
+
+#include "utils.h"
+
+at::Tensor get_dist(at::Tensor x, ptrdiff_t index) {
+  return (x - x[index]).norm(2, 1);
+}
+
+at::Tensor fps(at::Tensor x, at::Tensor batch, float ratio, bool random) {
+  auto batch_size = batch[-1].data<int64_t>()[0] + 1;
+
+  auto deg = degree(batch, batch_size);
+  auto cum_deg = at::cat({at::zeros(1, deg.options()), deg.cumsum(0)}, 0);
+  auto k = (deg.toType(at::kFloat) * ratio).ceil().toType(at::kLong);
+  auto cum_k = at::cat({at::zeros(1, k.options()), k.cumsum(0)}, 0);
+
+  auto out = at::empty(cum_k[-1].data<int64_t>()[0], batch.options());
+
+  auto cum_deg_d = cum_deg.data<int64_t>();
+  auto k_d = k.data<int64_t>();
+  auto cum_k_d = cum_k.data<int64_t>();
+  auto out_d = out.data<int64_t>();
+
+  for (ptrdiff_t b = 0; b < batch_size; b++) {
+    auto index = at::range(cum_deg_d[b], cum_deg_d[b + 1] - 1, out.options());
+    auto y = x.index_select(0, index);
+
+    ptrdiff_t start = 0;
+    if (random) {
+      start = at::randperm(y.size(0), batch.options()).data<int64_t>()[0];
+    }
+
+    out_d[cum_k_d[b]] = cum_deg_d[b] + start;
+    auto dist = get_dist(y, start);
+
+    for (ptrdiff_t i = 1; i < k_d[b]; i++) {
+      ptrdiff_t argmax = dist.argmax().data<int64_t>()[0];
+      out_d[cum_k_d[b] + i] = cum_deg_d[b] + argmax;
+      dist = at::min(dist, get_dist(y, argmax));
+    }
+  }
+
+  return out;
+}
+
+PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
+  m.def("fps", &fps, "Farthest Point Sampling (CPU)");
+}

setup.py

@@ -5,6 +5,7 @@ from torch.utils.cpp_extension import CppExtension, CUDAExtension, CUDA_HOME
 ext_modules = [
     CppExtension('graclus_cpu', ['cpu/graclus.cpp']),
     CppExtension('grid_cpu', ['cpu/grid.cpp']),
+    CppExtension('fps_cpu', ['cpu/fps.cpp']),
 ]
 cmdclass = {'build_ext': torch.utils.cpp_extension.BuildExtension}