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. src/java.base/share/classes/jdk/internal/foreign/SegmentBulkOperations.java line 210: > 208: long val = > SCOPED_MEMORY_ACCESS.getLongUnaligned(segment.sessionImpl(), > segment.unsafeGetBase(), segment.unsafeGetOffset() + fromOffset, > !Architecture.isLittleEndian()); > 209: result = result * POWERS_OF_31[7] > 210: + ((byte) (val >>> 56)) * POWERS_OF_31[6] I've manually checked the unrolling, and it seems correct test/jdk/java/foreign/TestSegmentBulkOperationsContentHash.java line 49: > 47: import static org.junit.jupiter.api.Assertions.*; > 48: > 49: final class TestSegmentBulkOperationsContentHash { Should we add a test which checks that the result of the content hash is the same as the polynomial described in the javadoc? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/22364#discussion_r1860486592 PR Review Comment: https://git.openjdk.org/jdk/pull/22364#discussion_r1860485622
