16. A computer readable medium including instructions which when processed by a computer, cause the computer to: receive an input value; determine a hash value for the input value according to a hash function, the hash function being operative to map distinct input values in a distinguished set of input values to distinct hash values in a set of hash values, and further operative to map all input values outside the distinguished set of input values to hash values outside the set of hash values; and compare the hash value for the input value to hash values previously determined for the distinguished set of input values according to the hash function, wherein the hash function includes a perfect hash function in combination with a second hash function, the second hash function being operative to map all input values included in the distinguished set of values to a first value, and further operative to map all input values outside the distinguished set of input values to one or more values different than the first value.
16. A computer readable medium including instructions which when processed by a computer, cause the computer to: receive an input value; determine a hash value for the input value according to a hash function, the hash function being operative to map distinct input values in a distinguished set of input values to distinct hash values in a set of hash values, and further operative to map all input values outside the distinguished set of input values to hash values outside the set of hash values; and compare the hash value for the input value to hash values previously determined for the distinguished set of input values according to the hash function, wherein the hash function includes a perfect hash function in combination with a second hash function, the second hash function being operative to map all input values included in the distinguished set of values to a first value, and further operative to map all input values outside the distinguished set of input values to one or more values different than the first value. 18. The computer readable medium of claim 16 , wherein the computer readable medium further includes instructions which when processed by a computer, cause the computer to determine each of the hash values by: encoding the input values as a binary decision diagram (BDD) created from a family of sets; associating positions of the BDD with bit positions of the hash values such that the input values are encoded into unique hash values dependent on the path of the BDD traversed by a particular input value.