Scale based on mouse proximity

1

I would like to scale a movie clip based on how close the mouse gets to it, but flash slows when there are a ton of these. I’m looking for a new method – any ideas?

onMouseMove = function(){
var dx:Number = this._x - _parent._xmouse;
var dy:Number = this._y - _parent._ymouse;
var dist:Number = Math.round(Math.sqrt(dxdx + dydy));
if (dist<100){
this._xscale = this._yscale = 200 - dist;
this._alpha += 2;
} else if (dist>100){
this._xscale = this._yscale = 100;
this._alpha = 20;
}
}