Block-Restricted Reordering - Extended Experiments

Ordered Binary Decision Diagrams (OBDDs) are so far the most eecient representation scheme for manipulation of Boolean functions in computer-aided design and veriication of digital systems. The concise-ness of an OBDD representation depends on the choice of the variable ordering, and the minimization problem that can be formulated as the problem of nding an ordering that minimizse the OBDD size is known to be NP-hard. Hence, considerable eeorts are done to develop eecient ordering heuristics that nd an acceptable solution. One of the best heuristics is a Sifting algorithm. The main drawback of Sifting is that, often, it is too time consuming. An acceleration eeect can be achieved by a method proposed by Meinel and Slobodovv a in their previous work: Based on structural properties that reeect a communication ow, OBDDs are cut into smaller parts that can be minimized separately. This idea applied to Sifting yields a method called Block-restricted Sifting. Motivated by the rst encouraging experimental results with this method, we work on its further development. The new ideas are evaluated in a series of experiments and reported here for a sample of benchmark circuits.