RFR 8203279 : Faster calculation of power of two (original) (raw)
David Holmes david.holmes at oracle.com
Thu May 17 01:12:11 UTC 2018
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Hi Ivan,
Surely you need to back this up with some performance numbers! And verify not assume that numberOfLeadingZeroes is intrinsified!
Cheers, David
On 17/05/2018 10:32 AM, Ivan Gerasimov 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.MINVALUE to Integer.MAXVALUE (including), to make sure the result is the same. For TimSort.ensureCapacity() I checked all positive values of minCapacity.
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