rotating a bone slows down frame rate considerably

I have an update loop that slows down considerably --going from 30fps to about 9 if I add the lines below that are commented out. The project moves a character’s feet depending on the mouse position.

Is there anything inherently slow about any of the commented lines?

	if( ||{

var steprotation=.1*((mousevec.x-Screen.width/2)/(Screen.width/2));
var steprotation2=.1*((mousevec.x-Screen.width/2)/(Screen.width/2));

Well this may not help much but I’ve heard its more efficient to multiply by .5 than to / by