If you specify n, it is the length of the final result in characters; after conversion the input string is sign-extended to the required length. If the number is too big to fit into n characters, it is truncated on the left. The n must be a positive whole number or zero.
If you omit n, wholenumber must be a positive whole number or zero, and the returned result has no leading zeros.
D2X(9) -> '9'
D2X(129) -> '81'
D2X(129,1) -> '1'
D2X(129,2) -> '81'
D2X(129,4) -> '0081'
D2X(257,2) -> '01'
D2X(-127,2) -> '81'
D2X(-127,4) -> 'FF81'
D2X(12,0) -> ''
Implementation maximum: The output string may not have more than 500 significant hexadecimal characters, though a longer result is possible if it has additional leading sign characters (0 and F).