Improved computational methods and lazy evaluation of the Ordered Ternary Decision Diagram

We investigate the properties of the Ordered Ternary Decision Diagram (OTDD) in order to develop an efficient general OTDD package. The OTDD is a three-branched three-terminal diagram based on Kleenean strong ternary logic. The OTDD can represent functions having nontrivial don't-care sets in a single diagram and is capable of provably correct evaluation in the presence of unknown input values. We propose a number of improvements to both OTDD computational methods and data structures. Furthermore we introduce the purged form OTDD which unifies the abbreviated and full form OTDD into a single diagram. A package exploiting these OTDD specific properties is presented and we show the computational advantages of this improved package for LGSynth93 standard benchmarks.