Explain the working of carry look-ahead adder with the help of an example.

A carry look-ahead adder finds all carries at once. It uses $G_i = A_iB_i$ and $P_i = A_i \oplus B_i$, with $C_{i+1} = G_i + P_iC_i$ and $S_i = P_i \oplus C_i$.

Example: add $A = 1011$ and $B = 0110$ with $C_0 = 0$. Here $G = 0010$ and $P = 1101$ (bit 3 to bit 0). The look-ahead equations give $C_1 = 0$, $C_2 = G_1 = 1$, $C_3 = G_2 + P_2G_1 = 1$ and $C_4 = 1$. The sums $P_i \oplus C_i$ are $S_3S_2S_1S_0 = 0001$, so the result is $10001 = 17$, which equals $11 + 6$.