BExIS.IO.Transform.Output.ExcelWriter.getColumnNumber C# (CSharp) Метод

        private static int getColumnNumber(string columnName)
        {
            char[] chars = columnName.ToCharArray();

            if (chars.Length == 1)
            {
                int colNr1 = (int)(chars[0] - 64);
                return colNr1;
            }
            else if (chars.Length == 2)
            {
                int colNr1 = (int)(chars[1] - 64);
                int colNr2 = (int)(chars[0] - 64);
                return colNr1 + (26 * colNr2);
            }
            else if (chars.Length == 3)
            {
                int colNr1 = (int)(chars[2] - 64);
                int colNr2 = (int)(chars[1] - 64);
                int colNr3 = (int)(chars[0] - 64);
                return colNr1 + (26 * colNr2) + (26 * 26 * colNr3);
            }
            else
            {
                return -1;
            }
        }