On Mon, 25 Nov 2024 15:27:13 GMT, Per Minborg <pminb...@openjdk.org> wrote:
> This PR proposes adding a _JDK-internal_ method for calculating hash codes > for content in a `MemorySegment`. > > The internal method uses a polynomial 32-bit hash function equivalent to > `Arrays::hashCode`. The new method is almost two times faster than naïvely > iterating over individual bytes for larger regions. Also, it is more lean on > inlining space compared to a naïve loop. > > > > Benchmark (ELEM_SIZE) Mode Cnt Score Error > Units > SegmentBulkHash.array 8 avgt 30 2.645 ? 0.078 > ns/op > SegmentBulkHash.array 64 avgt 30 6.062 ? 0.171 > ns/op > SegmentBulkHash.heapSegment 8 avgt 30 4.181 ? 0.145 > ns/op > SegmentBulkHash.heapSegment 64 avgt 30 25.716 ? 1.043 > ns/op > SegmentBulkHash.nativeSegment 8 avgt 30 3.939 ? 0.150 > ns/op > SegmentBulkHash.nativeSegment 64 avgt 30 23.262 ? 0.694 > ns/op > SegmentBulkHash.nativeSegmentJava 8 avgt 30 5.219 ? 0.183 > ns/op <- Naïve iteration > SegmentBulkHash.nativeSegmentJava 64 avgt 30 39.668 ? 1.040 > ns/op <- Naïve iteration > > >  > > > If internal JDK code uses this method, it will automatically benefit from > future performance improvements that can be implemented once the Vector API > becomes available. Nice work. Let's see how often this is used and then evaluate whether to promote to public API. Let's also investigate ways to make the autovectorizer kick in for such code shapes w/o having to manually unroll :-) ------------- Marked as reviewed by mcimadamore (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/22364#pullrequestreview-2464745357
