Better way to get line ranges in a UITextView

Question

Right now, I am able to get the text ranges of each line in a UITextView containing n lines by using cycling through the tokenizer with paragraph granularity. Unfortunately, that means my search algorithm for the m-th line in the text is of order n. Is there any easier way for me to find the range other than making my algorithm log n? The following is how I find my text range for now:

- (UITextRange *)textRangeOfLineAtIndex:(NSUInteger)index {

    UITextPosition *position = self.beginningOfDocument;

    NSUInteger lineCount = 0;
    while([self comparePosition:self.endOfDocument toPosition:position] == NSOrderedDescending && lineCount < index) {
        position = [self.tokenizer positionFromPosition:position toBoundary:UITextGranularityParagraph inDirection:UITextStorageDirectionForward];
        ++lineCount;
    }

    return [self rangeEnclosingPosition:position withGranularity:UITextGranularityParagraph inDirection:UITextStorageDirectionForward];

}