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 XOR-AND-OR forms with XOR 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 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.