Subtraction by Minuend Complementation

In performing the operation of subtraction in additive systems, a popular practice is to complement the subtrahend and add. A second method of performing subtraction, which seems to have been overlooked, is to complement the minuend, add it to the subtrahend, and complement the result. In many cases, this second method is more awkward; however, in two instances it seems to be worthy of consideration. The first instance, surprisingly enough, concerns BCD systems, where minuend complementation can compare favorably with more conventional methods of BCD subtraction. The second instance concerns negative radix numbers where the technique of minuend complementation seems to offer definite advantages.