The input must be a valid decimal number within the range [ -2^39, 2^39 - 1 ].
Excel internally represents Hexadecimal numbers in binary using 40 bits. The first bit indicates whether the number is positive or negative. The remaining bits indicate the magnitude of the number. Negative numbers are internally represented in binary using two's complement notation. Two's complement notation, when converted to hexadecimal, starts at the highest 10 digit hexadecimal number and goes backwards.