Slow animation of table view deceleration

Question

Trying to set targetContentOffset in scrollview delegate method to snap tableView to desired position(top,middle,bottom),but after snap action the tableView decelerate to the position but its not finishing animation very fast it gets slow down after few seconds.i tried to change the speed by putting some lower number (0.97,0.96…..) but still its is same,I have also tried putting the same content in UIView animation block but there is no change in speed? How Can I speed up deceleration Rate more than UIScrollViewDecelerationRateFast?

tableView.decelerationRate = UIScrollViewDecelerationRateFast
var scrollRect:CGRect = scrollView.frame;

func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {

    scrollRect.origin.y = self.getNextPosition(position, previousPosition: self.previousPosition, fastScroll: isFastScroll! , andScrollDirection: self.scrollDirection!,isFrameChanged:frameChanged)

    targetContentOffset.memory.y = scrollRect.origin.y
}