Use box.grow_low and grow_high

Python/pywarpx/fields.py

@@ -350,26 +350,20 @@ def _get_intersect_slice(self, mfi, starts, stops, icstart, icstop, with_interna
             The slice of the intersection relative to the global array where the data from individual block will go
         """
         box = mfi.tilebox()
-        box_small_end = box.small_end
-        box_big_end = box.big_end
         if self.include_ghosts:
             nghosts = self.mf.n_grow_vect()
             if with_internal_ghosts:
-                box.grow(self.mf.n_grow_vect())
-                box_small_end = box.small_end
-                box_big_end = box.big_end
+                box.grow(nghosts)
             else:
-                # When available, this could be somewhat simplified by using box.grow_low and box.grow_high,
-                # which would remove the need of the temporary copies of small_end and big_end.
                 min_box = self.mf.box_array().minimal_box()
                 for i in range(self.dim):
-                    if box_small_end[i] == min_box.small_end[i]:
-                        box_small_end[i] -= nghosts[i]
-                    if box_big_end[i] == min_box.big_end[i]:
-                        box_big_end[i] += nghosts[i]
+                    if box.small_end[i] == min_box.small_end[i]:
+                        box.grow_low(i, nghosts[i])
+                    if box.big_end[i] == min_box.big_end[i]:
+                        box.grow_high(i, nghosts[i])
 
-        ilo = self._get_indices(box_small_end, 0)
-        ihi = self._get_indices(box_big_end, 0)
+        ilo = self._get_indices(box.small_end, 0)
+        ihi = self._get_indices(box.big_end, 0)
 
         # Add 1 to the upper end to be consistent with the slicing notation
         ihi_p1 = [i + 1 for i in ihi]