zChaff: Modifications and Extensions

The application of SAT solver in industrial verificationtools is mandatory for the successful analysis of prob-lems derived from hardware design, e.g. CombinationalEquivalence Checking (CEC) and Bounded Model Check-ing (BMC). In [8] Chaff, a new powerful SAT solver, waspresented that outperforms most of the existing publiclyavailable SAT solvers when applied to hard real-world prob-lems, e.g. from VLSI CAD. There are two versions avail-able of Chaff: mChaff and zChaff. Both are instancesof Chaff, but from the viewpoint of implementation they aretotally different since they were developped independentlyby M. Moskewicz (mChaff) and L. Zhang (zChaff). Inthis paper we concentrate on zChaff. We analyze the coreissues and propose modifications and extensions.