  Polymorphic circuits are a special kind of digital logic components, which
possess multiple build-in functions. In different environments, a polymorphic
circuit would perform different functions. Evolutionary Algorithms, Binary
Decision Diagrams (BDD) and the multiplex method have been adopted to design
polymorphic circuits. However, the evolutionary methods face the scalable
problem. The BDD method consumes too much gate resource. The polymorphic
circuit built by the multiplex method rarely contains polymorphic gates. In
this paper, based on the traditional Bi_Decomposition circuit design approach,
two methods, i.e. the Poly_Bi_Decomposition method and the
Transformation&Bi_Decomposition method, are proposed for designing polymorphic
circuits. The Poly_Bi_Decomposition method can design relatively large and
gate-efficient polymorphic circuits with a higher percentage of polymorphic
gates. The Transformation&Bi_Decomposition method can use the traditional
circuit design approaches and tools, e.g. Bi_Decomposition, to design
polymorphic circuits directly. The experimental results show the good
performance of the proposed methods.
