Binary Decision Diagrams (BDDs) are the state-of-the-art data structure in VLSI CAD. since their size largely depends on the chosen variable ordering, dynamic variable reordering methods, like sifting, often have to be applied while the BDD for a given circuit is constructed. Usually sifting is called each time a given node limit is reached and it is therefire called frequently during the construction of large BDDs. Often most of the runtime is spent for sifting while the BDD is built.
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