On Wed, 18 Jan 2023 12:43:31 GMT, fabioromano1 <d...@openjdk.org> wrote:
>> The enanchment is useful for applications that make heavy use of BitSet >> objects as sets of integers, and therefore they need to make a lot of calls >> to cardinality() method, which actually require linear time in the number of >> words in use by the bit set. >> This optimization reduces the cost of calling cardinality() to constant >> time, as it simply returns the value of the field, and it also try to make >> as little effort as possible to update the field, when needed. >> >> Moreover, it has been implemented a new method for testing wheter a bit set >> includes another bit set (i.e., the set of true bits of the parameter is a >> subset of the true bits of the instance). > > fabioromano1 has updated the pull request incrementally with one additional > commit since the last revision: > > Added author and reverse the cicle order in includes(BitSet) I'll additionally note that there was a recent enhancement to enable vectorization of loops over `Long.bitCount(long)`, which should help `BitSet.cardinality()` calls by a large factor: https://bugs.openjdk.org/browse/JDK-8278868 - this can mean building up and then invoking an unchanged `cardinality()` is likely to be cheaper than the extra book-keeping to maintain a derived `cardinality` value. How does performance of `BitSet.cardinality()` compare before/after JDK 19? If there's a large improvement the need for this approach might have diminished. Perhaps caching the result of `cardinality()` is a less intrusive alternative, but as @JimLaskey is suggesting perhaps this would be better conceptualized as a subclass. ------------- PR: https://git.openjdk.org/jdk/pull/11837
