•Gi is called generate function and Pi is called propagate function.
•Gi and Pi are computed only from xi and yi and not ci, thus they can be computed in 1 gate delay after X and Y are applied to the inputs of an n-bit adder.
•All carries can be obtained 3 gate delays after X, Y and c0 are applied.
-One gate delay for Pi and Gi
-Two gate delays in the AND-OR circuit for ci+1
•All sums can be obtained 1 gate delay after the carries are computed.
•Independent of n, n-bit addition requires only 4 gate delays.
•This is called Carry-Lookahead adder.