One-Pass Design of Reversible Circuits: Combining Embedding and Synthesis for Reversible Logic

Reversible computation is a heavily investigated emerging technology due to its promising characteristics in low-power design, its application in quantum computations, and several further application areas. The currently established functional synthesis flow for reversible circuits is composed of two distinct steps. First, an embedding process is conducted which makes nonunique output patterns distinguishable by adding further variables. Then, this function is passed to a synthesis method which eventually yields a reversible circuit. However, the separate consideration of the embedding and synthesis tasks leads to significant drawbacks. In fact, embedding is not necessarily conducted in a fashion which is suited for the following synthesis process. In addition, embedding adds further variables to the function to be synthesized which exponentially increases its corresponding representation in the worst case. In this paper, we propose one-pass design of reversible circuits, which combines embedding and synthesis. This allows for conducting synthesis with a high degree of freedom, since the embedding that suits best is inherently chosen during synthesis. We propose two solutions (an exact an a heuristic one) following this scheme that improve the currently established synthesis flow by magnitudes in terms of runtime-allowing to synthesize a reversible circuit with a minimum number of lines for some of the frequently considered benchmark functions for the first time. Furthermore, a significant reduction of the costs of the resulting circuits (up to several orders of magnitude) is achieved with this new design flow.