Hybrid LZA: A near optimal implementation of the Leading Zero Anticipator

The Leading Zero Anticipator (LZA) is one of the main components used in floating point addition. It tends to be on the critical path, so it has attracted the attention of many researchers in the past. Most LZAs used today can be classified in two categories: exact and inexact. Inexact LZAs are normally preferred due to their shorter critical paths and reduced complexity; however, the inexact LZA requires an additional correct stage. In this paper we present a new LZA architecture that combines ideas taken from prior exact and inexact LZAs. Our new LZA improves the delay of floating point addition by 7-10% compared to state of art techniques as well as reduces hardware area in most cases. We also establish theoretical lower bounds on the delay of an LZA and we show that our LZA is very close to these bounds.