An "open" BitSet implementation that allows direct access to the array of words storing the bits.
Unlike java.util.bitet, the fact that bits are packed into an array of longs is part of the interface. This allows efficient implementation of other algorithms by someone other than the author. It also allows one to efficiently implement alternate serialization or interchange formats.
OpenBitSet is faster than
java.util.BitSet in most operations and *much* faster at calculating cardinality of sets and results of set operations. It can also handle sets of larger cardinality (up to 64 * 2**32-1)
The goals of
OpenBitSet are the fastest implementation possible, and maximum code reuse. Extra safety and encapsulation may always be built on top, but if that's built in, the cost can never be removed (and hence people re-implement their own version in order to get better performance). If you want a "safe", totally encapsulated (and slower and limited) BitSet class, use
java.util.BitSet.
Performance Results
Test system: Pentium 4, Sun Java 1.5_06 -server -Xbatch -Xmx64M
BitSet size = 1,000,000
Results are java.util.BitSet time divided by OpenBitSet time.
| cardinality | intersect_count | union | nextSetBit | get | iterator |
| 50% full | 3.36 | 3.96 | 1.44 | 1.46 | 1.99 | 1.58 |
| 1% full | 3.31 | 3.90 | | 1.04 | | 0.99 |
Test system: AMD Opteron, 64 bit linux, Sun Java 1.5_06 -server -Xbatch -Xmx64M
BitSet size = 1,000,000
Results are java.util.BitSet time divided by OpenBitSet time.
| cardinality | intersect_count | union | nextSetBit | get | iterator |
| 50% full | 2.50 | 3.50 | 1.00 | 1.03 | 1.12 | 1.25 |
| 1% full | 2.51 | 3.49 | | 1.00 | | 1.02 |
@version $Id$