1. A carry-look ahead adder (CLA) or fast adder is a type of adder used in digital logic circuits. A carry-look ahead adder improves speed by reducing the amount of time required to determine carry bits.

2. To reduce the computation time, there are faster ways to add two binary numbers by using carry look ahead adders.

3. They work by creating two signals P and G known to be Carry Propagator and Carry Generator. The carry propagator is propagated to the next level whereas the carry generator is used to generate the output carry, regardless of input carry.

4. The block diagram of a 4-bit Carry Look ahead Adder is shown here below 

5. Carry lookahead depends on two things:

i) Calculating, for each digit position, whether that position is going to propagate a carry if one comes in from the right.

ii) Combining these calculated values to be able to deduce quickly whether, for each group of digits, that group is going to propagate a carry that comes in from the right.