iphone - cocos2d-iphoneでスプライトを180度回転させるには?

Question

-(void) ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event
    {
        CGPoint location = [touch locationInView:[touch view]];
        location = [[CCDirector sharedDirector] convertToGL:location];

        shootVector = ccpSub(location, cannon.position);
        CGFloat shootAngle = ccpToAngle(shootVector);
        cocosAngle = CC_RADIANS_TO_DEGREES(-1 * shootAngle);

        CGFloat rotateDiff = cocosAngle;    
        if (rotateDiff > 180)
            rotateDiff -= 360;
        if (rotateDiff < -180)
            rotateDiff += 360;    

        CGFloat rotateSpeed = 360; 
        rotateDuration = fabs(rotateDiff / rotateSpeed);

        [cannon runAction:[CCSequence actions:
                           [CCRotateTo actionWithDuration:rotateDuration angle:cocosAngle],
                           [CCCallFunc actionWithTarget:nil selector:nil],
                           nil]];

        top.rotation = cannon.rotation;
    }

上記のコードでは、360 度移動したタッチで回転が発生します。代わりに、大砲を 180 度以下で回転させたい..

どんな助けでも大歓迎です。