Multilevel reverse most-significant carry computation
J.D. Bruguera, Thomas A. Lang · IEEE Transactions on Very Large Scale Integration (VLSI) Systems · 2001
A fast calculation of the most-significant carry in an addition is required in several applications. It has been proposed to calculate this carry by detecting the most-significant carry chain and collecting the carry after this chain. The detection can be implemented by a prefix tree of AND gates and the collecting by a multi-input OR. We propose a multilevel implementation, which allows the overlap of successive levels, thereby reducing the overall delay. For 64-bit operands we estimate a delay reduction of about 15% with respect to the traditional carry-lookahead-based method, with a similar hardware complexity.