In
electronics, a
subtractor can be designed using the same approach as that of an
adder. The
binary subtraction process is summarized below. As with an adder, in the general case of calculations on multi-bit numbers, three
bits are involved in performing the subtraction for each bit of the
difference: the
minuend (
),
subtrahend (
), and a borrow in from the previous (less significant) bit order position (
). The outputs are the difference bit (
) and borrow bit
. The subtractor is best understood by considering that the subtrahend and both borrow bits have negative weights, whereas the X and D bits are positive. The operation performed by the subtractor is to rewrite
(which can take the values -2, -1, 0, or 1) as the sum
.