AC_WPNav: use fast_atan2 for bearing calcs

libraries/AC_WPNav/AC_WPNav.cpp

@@ -822,7 +822,7 @@ void AC_WPNav::advance_spline_target_along_track(float dt)
         _pos_control.set_pos_target(target_pos);
 
         // update the yaw
-        _yaw = RadiansToCentiDegrees(atan2f(target_vel.y,target_vel.x));
+        _yaw = RadiansToCentiDegrees(fast_atan2(target_vel.y,target_vel.x));
 
         // advance spline time to next step
         _spline_time += _spline_time_scale*dt;
@@ -861,7 +861,7 @@ void AC_WPNav::calc_spline_pos_vel(float spline_time, Vector3f& position, Vector
 // To-Do: move this to math library
 float AC_WPNav::get_bearing_cd(const Vector3f &origin, const Vector3f &destination) const
 {
-    float bearing = 9000 + atan2f(-(destination.x-origin.x), destination.y-origin.y) * 5729.57795f;
+    float bearing = 9000 + fast_atan2(-(destination.x-origin.x), destination.y-origin.y) * 5729.57795f;
     if (bearing < 0) {
         bearing += 36000;
     }