code: private static int decode(final int hex) {
          if (hex >= CcHex.BACK.length) {
              throw new DecodingException(
                  String.format("invalid hex char: 0x%2x", hex)
              );
          }
          final int dec = CcHex.BACK[hex];
          if (dec < 0) {
              throw new DecodingException(
                  String.format("invalid hex character: 0x%2x", hex)
              );
          }
          return dec;
      }
docs: Convert hex to number.
  @param hex Hex number
  @return Decoded