Patent US 4,218,751

An absolute difference generator comprises an adder, an Exclusive-OR, two inverters and a latch. One input number is inverted, then presented to one input of the adder while the other input number is presented to the other input of the adder. The carry out line of the adder sets a latch, the output of which is fed back to the carry in line of the adder. The latch output is also combined with the adder output in an Exclusive-OR to control inversion of the adder output and produce the absolute difference between the input data.