Dynamic evaluation and adaption of hardware hash functions
Creating hash values based on bit values of an input vector. An apparatus includes a first and a second hash table, a first and second hash function generator adapted to configure a respective hash function for a creation of a first and second hash value based on the bit values of the input vector. The hash values are stored in the respective hash tables. An evaluation unit includes a comparison unit to compare a respective effectiveness of the first hash function and the second hash function, and an exchanging unit responsive to the comparison unit adapted to replace the first hash function by the second hash function.
1. An apparatus for creating hash values based on bit values of an input vector, the apparatus comprising:
a first hash table;
a first hash function generator configured to configure a first hash function for creation of a first hash value based on the bit values of the input vector, the first hash value to be stored in the first hash table; and
an evaluation unit responsive to the bit values of the input vector to test a second hash function, the evaluation unit comprising:
a second hash table with fewer entries than the first hash table;
a second hash function generator configured to configure the second hash function for creation of a second hash value based on the bit values of the input vector, the second hash value to be stored in the second hash table;
a comparison unit to compare an effectiveness of the first hash function with an effectiveness of the second hash function; and
an exchanging unit responsive to the comparison unit configured to replace the first hash function with the second hash function; and
a hash function mask unit configured to be activated after the replacement of the first hash function with the second hash function, and configured to limit comparisons to those bits of a new hash value of the second hash function, which has replaced the first hash function, that are identically generated if compared to the first hash function.
2. The apparatus of claim 1 , wherein the input vector represents an address value readable by a processor.
3. The apparatus of claim 1 , wherein a subset of bits of the input vector is used as input values for a group of hash bit logic units of the first hash function and for a group of hash bit logic units of the second hash function, wherein each hash bit logic unit of the group of hash bit logic units of the first hash function is differently configurable, and wherein each hash bit logic unit of the group of hash bit logic units of the first hash function generates one bit (H( 0 ), H( 1 ), . . . , H(m- 1 )) of a hash function value generated by the first hash function.
4. The apparatus of claim 1 , wherein the replacement of the first hash function with the second hash function is performed without delaying an input stream of the bit values of the input vector.
5. The apparatus of claim 1 , wherein the hash function mask is a bit mask having a number of bits of the hash value of the first hash function.
6. The apparatus of claim 1 , wherein a new hash value based on the second hash function is compared to entries of the second hash table.
7. The apparatus of claim 1 , wherein based on the replacement of the first hash function with the second hash function and until a condition is met, a matching of new hash values to at least one hash table entry of the first hash table is assumed.
8. A computer program product for creating hash values based on bit values of an input vector, the computer program product comprising
a non-transitory computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising:
configuring a first hash function for creation of a first hash value based on the bit values of the input vector, the first hash value to be stored in a first hash table;
configuring a second hash function for creation of a second hash value based on the bit values of the input vector, the second hash value to be stored in a second hash table, the second hash table having fewer entries than the first hash table;
comparing an effectiveness of the first hash function with an effectiveness of the second hash function;
based on the comparing, replacing the first hash function with the second hash function; and
limiting, by a hash function mask unit configured to be activated after the replacement of the first hash function with the second hash function, comparisons to those bits of a new hash value of the second hash function, which has replaced the first hash function, that are identically generated if compared to the first hash function.
9. The computer program product of claim 8 , wherein the input vector represents an address value readable by a processor.
10. The computer program product of claim 8 , wherein a subset of bits of the input vector is used as input values for a group of hash bit logic units of the first hash function and for a group of hash bit logic units of the second hash function, wherein each hash bit logic unit of the group of hash bit logic units of the first hash function is differently configurable, and wherein each hash bit logic unit of the group of hash bit logic units of the first hash function generates one bit (H( 0 ), H( 1 ), . . . , H(m- 1 )) of a hash function value generated by the first hash function.
11. The computer program product of claim 8 , wherein the replacement of the first hash function with the second hash function is performed without delaying an input stream of the bit values of the input vector.
12. The computer program product of claim 8 , wherein the hash function mask is a bit mask having a number of bits of the hash value of the first hash function.
13. The computer program product of claim 10 , wherein a new hash value based on the second hash function is compared to entries of the second hash table.
14. A method of creating hash values based on bit values of an input vector, the method comprising:
configuring a first hash function for a creation of a first hash value based on the bit values of the input vector, the first hash value to be stored in a first hash table;
configuring a second hash function for a creation of a second hash value based on the bit values of the input vector, the second hash value to be stored in a second hash table, the second hash table having fewer entries than the first hash table;
comparing an effectiveness of the first hash function with an effectiveness of the second hash function;
based on the comparing, replacing the first hash function with the second hash function; and
limiting, by a hash function mask unit configured to be activated after the replacement of the first hash function with the second hash function, comparisons to those bits of a new hash value of the second hash function, which has replaced the first hash function, that are identically generated if compared to the first hash function.
15. The method of claim 14 , wherein the input vector represents an address value readable by a processor.
16. The method of claim 14 , wherein a subset of bits of the input vector is used as input values for a group of hash bit logic units of the first hash function and for a group of hash bit logic units of the second hash function, wherein each hash bit logic unit of the group of hash bit logic units of the first hash function is differently configurable, and wherein each hash bit logic unit of the group of hash bit logic units of the first hash function generates one bit (H( 0 ), H( 1 ), . . . , H(m- 1 )) of a hash function value generated by the first hash function.
17. The method of claim 14 , wherein the hash function mask is a bit mask having a number of bits of the hash value of the first hash function.