Reversible Logic Synthesis with Output Permutation

Synthesis of reversible logic has become a very important research area. In recent years several algorithms--heuristic as well as exact ones--have been introduced in this area. Typically, they use the specification of a reversible function in terms of a truth table as input. Here, the position of the outputs are fixed. However, in general it is irrelevant, how the respective outputs are ordered. Thus, a synthesis methodology is proposed that determines for a given reversible function an equivalent circuit realization modulo output permutation. More precisely, the result of the synthesis process is a circuit realization whose output functions have been permuted in comparison to the original specification and the respective permutation vector. We show that this synthesis methodology may lead to significant smaller realizations. We apply Synthesis with Output Permutation (SWOP) to both, an exact and a heuristic synthesis algorithm. As our experiments show using the new synthesis paradigm leads to multiple control Toffoli networks that are smaller than the currently best known realizations.