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

[Ivan Gerasimov]

Thanks, Mike!

Yes, I need a sponsor and would really appreciate your help.

Sincerely yours,
Ivan

On 30.07.2013 20:32, Mike Duigou wrote:
> 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?
>
> Mike
>
> 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
>
>