Restructuring logic representations with easily detectable simple disjunctive decompositions

Simple disjunctive decomposition is a special case of logic function decomposition, where variables are divided into two disjoint sets and there is only one newly introduced variable. This paper presents that many simple disjunctive decompositions can be found easily by detecting symmetric variables or checking variable cofactors. We also propose an algorithm that constructs a new logic representation for a simple disjunctive decomposition by assigning constant values to variables in the original representation. The algorithm enables us to apply the decomposition with keeping good structures of the original representation. We have performed experiments to restructure fanout free cones of multi-level logic circuits, and obtained better results than when not restructuring them.