Complex Rotating Turret (AS2)

I'm trying to make a turret that points towards the cursor, but lags when the cursor is moved. I can get this to work, however I am running into problems when the cursor crosses from quadrant 4 to 3 (and vice versa). The problem is that the function I am using to control the turret's rotation rotates the turret around the opposite direction almost 360 degrees to get to the new position, instead of moving the few degrees it needs to. Here is a picture to help explain.
http://img293.imageshack.us/img293/1707/helpmeeee.jpg

So what is your current code?

see this thread here

gparis

My code looks like so:

Actionscript Code:

onClipEvent (enterFrame) {
    xdiff = this._x-_root.cursor._x;
    ydiff = this._y-_root.cursor._y;
    hyp = Math.sqrt(Math.pow(xdiff, 2)+Math.pow(ydiff, 2));
    phi = (180/Math.PI)*Math.asin(ydiff/hyp);
    if (xdiff>0) {
        phi = 90-phi;
        this._rotation -= (0.1)*(this._rotation+phi);
    } else if (xdiff<0) {
        phi = phi-90;
        this._rotation -= (0.1)*(this._rotation+phi);
    }
}

It has some more bells and whistles to it but this is the important part.