iOS-Swift adjust font size to fit in rect

UILabel+FontSize.Swift

//
//  UILabel+FontSize.Swift
//
//  Created by Nutchaphon Rewik on 7/11/15.
//  Copyright (c) 2015 Nutchaphon Rewik. All rights reserved.
//

import UIKit

extension UILabel{
    
    func adjustFontSizeToFitRect(rect : CGRect){
        
        if text == nil{
            return
        }
        
        frame = rect
        
        var maxFontSize: CGFloat = 100.0
        let minFontSize: CGFloat = 5.0
        
        var q = Int(maxFontSize)
        var p = Int(minFontSize)
        
        let constraintSize = CGSize(width: rect.width, height: CGFloat.max)
        
        while(p <= q){
            let currentSize = (p + q) / 2
            font = font.fontWithSize( CGFloat(currentSize) )
            let text = NSAttributedString(string: self.text!, attributes: [NSFontAttributeName:font])
            let textRect = text.boundingRectWithSize(constraintSize, options: .UsesLineFragmentOrigin, context: nil)
            
            let labelSize = textRect.size
            
            if labelSize.height < frame.height &&
                labelSize.height >= frame.height-10 &&
                labelSize.width < frame.width &&
                labelSize.width >= frame.width-10 {
                break
            }else if labelSize.height > frame.height || labelSize.width > frame.width{
                q = currentSize - 1
            }else{
                p = currentSize + 1
            }
        }
        
    }
}

It doesn't work as I expected, just takes max fontSize. =(

Aug 8 2015... damn
I was at home, playing Battlefield 3 on Noshahr Canals, running around with knife and X-BOW