5. Embedding of Irreversible Functions

Quite often reversible circuits should be synthesized for irreversible functions. Thus, the problem of embedding is an important aspect. For this purpose, additional lines are introduced resulting in constant inputs, garbage outputs, and don’t care conditions, which have to be assigned to concrete values. Further options exist how (i.e. in which order) to arrange the outputs in the circuit to be synthesized. Overall, functions can be embedded in different ways whereby the concrete don’t care assignments as well as the chosen output arrangement may have a significant impact on the resulting circuit size. In this chapter, the different aspects of embedding mentioned above are investigated in detail. First, strategies for the don’t care assignment. Afterwards, the order of outputs in the function to be synthesized is considered.