Patent ID: 7899860

Claim:
A method of generating an input carry using estimated propagated carries in a carry look-ahead (CLA) adder, the method comprising: using an estimator circuit to generate an estimate of a previous carry-in, the estimator circuit operating with binary signals for operands Ai and Bi that are used by the adder and are provided to the estimator circuit as well as the CLA adder, wherein an estimated carry in Ci (estimated) of operands Ai and Bi is equal to Ai+Bi, the estimator circuit using a logic function that is independent of previous carries and that covers every logical 1 generated by use of one from among a Karnaugh Map, a Quine-McClusky table, or a table that identifies with the logical 1 value all possible operand combinations that generate a propagated carry in the CLA adder; and when a recursive depth is 1, the method further including implementing the circuit to use the estimated previous carry-in to generate the input carry corresponding to Ci+1=Gi+Pi·Ci−1 (estimated), and when the recursive depth is 2, the input carry corresponds to Ci+1=Gi+Pi·Gi−1+Pi·Pi−1·Ci−2 (estimated).