ATOI in Swift

atoi.swift

/*
* Converts ASCII string to an Int where plausible
* @param {String} str   the string passed to atoi
* return {Int?} the converted integer value
*/
func atoi(str: String) -> Int? {

	// Trim trailing whitespace
	var newStr:String = str.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())

	// Get length of string
	var newStrLen:Int = count(newStr)

	if (newStrLen < 1) {
		println("String is empty")
		return nil
	}

	var i:Int = 0
	var firstChar:Character = newStr[newStr.startIndex]
	var posNegMultiplier:Int = 1

	// Cater for negative numbers
	if (firstChar == "-") {
		posNegMultiplier = -1
		i++
	}

	// Init character array to iterate
	var characters:Array<Character> = Array(newStr)

	// Init cast variables
	var currLetter:String = ""

	// Prepare result
	var result:String = ""

	do {

		// Get string version of current character
		currLetter = String(characters[i])

		// Ensure it is not null
		if (!currLetter.isEmpty) {

			// Check if number
			if (currLetter >= "0" &&  currLetter <= "9") {
				result = "\(result)\(currInt)"
			}
		}

		++i;
	} while (i < newStrLen)

	// Return nil if no result from passed string
	if (result.isEmpty) {
		return nil
	}

	// Check for integer overflow
	var resultAsDouble:Double = Double((NSString(string: result).doubleValue * Double(posNegMultiplier)))
	if (resultAsDouble > Double(Int.max) || resultAsDouble < Double(Int.min)) {
		println("Error: Integer too large")
		return nil
	}

	// Pass the result back with multiplier
	return result.toInt()! * posNegMultiplier
}

This needs mucho improvementso, quick job