Variants of an improved carry look-ahead adder

An improved variation on the carry look-ahead adder has been proposed by H. Ling (IBM J. Res. Develop., vol.25, p.156, May 1981). Ling´s approach is based on the propagation of a composite term in place of the conventional look-ahead carry. This approach gives an adder that is faster and less expensive. In the present study, Ling´s adder is introduced and described in a general manner in order to expose the essence of his approach. From this reformulation, it is shown that there are many such variations on the carry look-ahead adder, a few of which share the desirable properties of Ling´s adder