fix(mgb/opr): correct nvof out shape computation

GitOrigin-RevId: 16bf086e92125cba867d9b935bb487363602014e

imperative/python/megengine/functional/vision.py

@@ -633,7 +633,8 @@ def nvof(src: Tensor, precision: int = 1) -> Tensor:
     :src shape: input tensor with shape (n, t, h, w, c4).
     :src dtype: uint8.
     :param precision: 0:NV_OF_PERF_LEVEL_SLOW 1:NV_OF_PERF_LEVEL_MEDIUM 2:NV_OF_PERF_LEVEL_FAST.
-    :output shape: (n, t-1, h//4, w//4, c2).
+    :output shape: ``(n, t-1, (h+out_grid_size-1)//out_grid_size, (w+out_grid_size-1)//out_grid_size, c2)``.
+        By default, out_grid_size = 4.
     :output dtype: int16.
 
     .. code-block:: python

src/opr/impl/misc.cpp

@@ -224,6 +224,7 @@ void NvOf::scn_do_execute() {
 void NvOf::init_output_static_infer_desc() {
     using namespace cg::static_infer;
     auto infer_shape = [](TensorShape& dest, const InpVal& iv) {
+        auto out_grid_size = NV_OF_OUTPUT_VECTOR_GRID_SIZE_4;
         auto ishp = iv.val.at(0).shape();
         //! nvof input format: nthwc4
         mgb_assert(ishp.ndim == 5);
@@ -232,8 +233,8 @@ void NvOf::init_output_static_infer_desc() {
         SmallVector<size_t> tv;
         tv.push_back(ishp[0]);
         tv.push_back(ishp[1] - 1);
-        tv.push_back(ishp[2] / 4);
-        tv.push_back(ishp[3] / 4);
+        tv.push_back((ishp[2] + out_grid_size - 1) / out_grid_size);
+        tv.push_back((ishp[3] + out_grid_size - 1) / out_grid_size);
         tv.push_back(ishp[4] / 2);
         dest = tv;