Speeding up Pseudo-Boolean Propagation

Unit propagation is known to be one of the most time-consuming procedures inside CDCL-based SAT solvers. Not surprisingly, it has been studied in depth and the two-watched-literal scheme, enhanced with implementation details boosting its performance, has emerged as the dominant method. In pseudo-Boolean solvers, the importance of unit propagation is similar, but no dominant method exists: counter propagation and watched-based extensions are efficient for different types of constraints, which has opened the door to hybrid methods. However, probably due to the higher complexity of implementing pseudo-Boolean solvers, research efforts have not focused much on concrete implementation details for unit propagation but rather on higher-level aspects of other procedures, such as conflict analysis. In this paper, we present (i) a novel methodology to precisely assess the performance of propagation mechanisms, (ii) an evaluation of implementation variants of the propagation methods present in {RoundingSat} and (iii) a detailed analysis showing that hybrid methods outperform the ones based on a single technique. Our final contribution is to show that a carefully implemented hybrid propagation method is considerably faster than the preferred propagation mechanism in {RoundingSat}, and that this improvement leads to a better overall performance of the solver.

Authors

• Robert Nieuwenhuis
• Albert Oliveras
• Enric Rodríguez-Carbonell
• Rui Zhao

Keywords

• SAT
• Pseudo-Boolean Solving
• Implementation-level Details