RFR [7192942] Optimizing calculation of power of 2 in HashMap

Mike Duigou mike.duigou at oracle.com
Tue Jul 30 16:32:04 UTC 2013

Hi Ivan;

This looks like a good improvement. My only disappointment is that I didn't notice it when adding the roundUpToPowerOf2 method!

Do you need a sponsor to push the fix?


On Jul 30 2013, at 08:35 , Ivan Gerasimov wrote:

> Hello everybody!
> HashTable needs to calculate the power of two that is not less that the given number.
> This calculation used to be implemented as a relatively inefficient loop (that's why the issue 7192942 was created).
> The implementation was improved with http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/2e3cc7f599ca
> However it can be improved even more. I reused 7192942 number for this propose.
> Would you please help with reviewing?
> Here's the webrev: http://cr.openjdk.java.net/~igerasim/7192942/0/webrev/ <http://cr.openjdk.java.net/%7Eigerasim/7192942/0/webrev/>
> I also created a benchmark test to make sure the improvement is observable.
> Here's the jmh benchmark I used:
> http://cr.openjdk.java.net/~igerasim/bench/powoftwo/src/main/java/org/benches/PowerOfTwoBench.java <http://cr.openjdk.java.net/%7Eigerasim/bench/powoftwo/src/main/java/org/benches/PowerOfTwoBench.java>
> Benchmark                                Mode Thr    Cnt Sec         Mean   Mean error    Units
> o.b.PowerOfTwoBench.benchPowerOfTwoA     avgt   1     20 5       60.697        0.850  msec/op
> o.b.PowerOfTwoBench.benchPowerOfTwoB     avgt   1     20 5       53.013        0.940  msec/op
> The first line is for the current implementation and the second one is for the proposed change.
> Thus, the time gets reduced by 12%.
> Sincerely yours,
> Ivan

More information about the core-libs-dev mailing list