Carry-lookahead Adder

A carry-lookahead adder (CLA) is a type of adder used in digital logic. A carry-lookahead adder improves speed by reducing the amount of time required to determine carry bits. It can be contrasted with the simpler, but usually slower, ripple carry adder for which the carry bit is calculated alongside the sum bit, and each bit must wait until the previous carry has been calculated to begin calculating its own result and carry bits (see adder for detail on ripple carry adders). The carry-lookahead adder calculates one or more carry bits before the sum, which reduces the wait time to calculate the result of the larger value bits. The Kogge-Stone adder and Brent-Kung adder are examples of this type of adder.

Charles Babbage recognized the performance penalty imposed by ripple carry and developed mechanisms for anticipating carriage in his computing engines. Gerald Rosenberger of IBM filed for a patent on a modern binary carry-lookahead adder in 1957.

Read more about Carry-lookahead Adder:  Theory of Operation, Carry Lookahead Method, Implementation Details, Manchester Carry Chain