Efficient minimization of fully testable 2-SPP networks

The paper presents a heuristic algorithm for the minimization of 2-SPP networks, i.e., three-level EXOR-AND-OR forms with EXOR gates restricted to fan-in 2. Previous works had presented exact algorithms for the minimization of unrestricted SPP networks and of 2-SPP networks. The exact minimization procedures were formulated as covering problems as in the minimization of SOP forms and had worst-case exponential complexity. Extending the expand-irredundant-reduce paradigm of the ESPRESSO heuristic, we propose a minimization algorithm for 2-SPP networks that iterates local minimization and reshape of a solution until further improvement. We introduce also the notion of EXOR-irredundant to prove that OR-AND-EXOR irredundant networks are fully testable and guarantee that our algorithm yields OR-AND-EXOR irredundant solutions. We report a large set of experiments showing impressive high-quality results with affordable run times, handling also examples whose exact solutions could not be computed.