Sibling-substitution-based BDD minimization using don't cares

In many computer-aided design tools, binary decision diagrams (BDD's) are used to represent Boolean functions. To increase the efficiency and capability of these tools, many algorithms have been developed to reduce the size of the BDD's. This paper presents heuristic algorithms to minimize the size of the BDD's representing incompletely specified functions by intelligently assigning don't cares to binary values. Experimental results show that new algorithms yield significantly smaller BDD's compared with existing algorithms yet still require manageable run-times. These algorithms are particularly useful for synthesis application where the structure of the hardware/software is derived from the BDD representation of the function to implement because the minimization quality is more critical than the minimization speed in these applications.