Hello Ivan, I've wondered about this myself. Probably the performance is architecture dependent. Probably a new method should be added to Integer and Long with @HotspotIntrinsicCandidate. That gives David another chance to practice his blind aarch64 assembly language coding skills. It's hard to give a good name for this. Hacker's delight calls it dclp2 and we can probably do better than that. http://www.hackersdelight.org/hdcodetxt/clp2.c.txt But I approve either way.
On Wed, May 16, 2018 at 5:32 PM, Ivan Gerasimov <ivan.gerasi...@oracle.com> wrote: > Hello! > > In a few places we have code that rounds an integer up to the nearest > power of two. > > It is done with a series of RSHOTFs and ORs, but it can possibly be done > faster with the use of Integer.numberOfLeadingZeros (assuming it is > intrinsified). > > Would you please help review this trivial optimization: > > BUGURL: https://bugs.openjdk.java.net/browse/JDK-8203279 > WEBREV: http://cr.openjdk.java.net/~igerasim/8203279/00/webrev/ > > For HashMap.tableSizeFor() I created a simple test with a loop from > Integer.MIN_VALUE to Integer.MAX_VALUE (including), to make sure the result > is the same. > > For TimSort.ensureCapacity() I checked all positive values of minCapacity. > > -- > With kind regards, > Ivan Gerasimov > >
