FRACTION_DENOM
tmp = ((value - fx(2)) * 256 * FRACTION_DENOM) / size;
mousedev->packet.dx = tmp / FRACTION_DENOM;
tmp - mousedev->packet.dx * FRACTION_DENOM;
tmp = -((value - fy(2)) * 256 * FRACTION_DENOM) / size;
mousedev->packet.dy = tmp / FRACTION_DENOM;
mousedev->packet.dy * FRACTION_DENOM;