gistfile1.cpp

    for (i = BTN_MOUSE; i < BTN_JOYSTICK; i++)
      if (test_bit( i, keybit ))
        num_buttons++;
//...then some other stuff
//then this...
/* Mouse, Touchscreen or Smartpad ? */
  if ((test_bit( EV_KEY, evbit ) && (test_bit( BTN_TOUCH, keybit )
      || test_bit( BTN_TOOL_FINGER, keybit ))) || ((num_rels >= 2
      && num_buttons) || (num_abs == 2 && (num_buttons == 1))))
    m_deviceType |= LI_DEVICE_MOUSE;
  else if (num_abs && num_buttons) /* Or a Joystick? */
    m_deviceType |= LI_DEVICE_JOYSTICK;