US Patent 7904842 Modifying a logic implementation by swapping inputs of fanout-free cones

An implementation of a logic description is improved. The implementation has two signals coupled to two inputs of a fanout-free cone. A swap function is determined of the inputs of the fanout-free cone. The swap function indicates whether there is a difference at an output of the fanout free cone between the fanout-free cone with and without swapping the two signals between the two inputs of the fanout-free cone. A do-not-care function of the inputs of the fanout-free cone is determined for the logic description. The do-not-care function indicates that a modification of the output of the fanout-free cone is not observable at the primary outputs of the logic description. A modified implementation of the logic description is output in response to the do-not-care function covering the swap function. The modified implementation of the logic description has the two signals swapped between the two inputs of the fanout-free cone.