    public static String addSeparators(
        String orig, char separator, int between)
    {
        StringBuffer buf = new StringBuffer(orig);
        int len = orig.length();
        buf.ensureCapacity(len + (len - 1) / between);

        for (int pos = len - between; pos > 0; pos -= between)
            buf.insert(pos, separator);
        return buf.toString();
    }
