Carry-skip adder

A carry-skip adder (also known as a carry-bypass adder) is an adder implementation that improves on the delay of a ripple-carry adder with little effort compared to other adders. The improvement of the worst-case delay is achieved by using several carry-skip adders to form a block-carry-skip adder.

The worst case for a simple one level carry-ripple-adder occurs, when the propagate-condition is true for each digit pair ${\displaystyle (a_{i},b_{i})}$. Then the carry-in ripples through the ${\displaystyle n}$-bit adder and appears as the carry-out after ${\displaystyle \tau _{CRA}(n)\approx n\cdot \tau _{VA}}$.

...
Wikipedia