Carry-select adder using single ripple-carry adder

Instead of using dual carry-ripple adders, a carry select adder scheme using an add-one circuit to replace one carry-ripple adder requires 29.2% fewer transistors with a speed penalty of 5.9% for bit length n=64. If speed is crucial for this 64 bit adder, then two of the original carry-select adder blocks can be substituted by the proposed scheme with a 6.3% area saving and the same speed