RFR  Optimizing calculation of power of 2 in HashMap
ivan.gerasimov at oracle.com
Tue Jul 30 15:35:10 UTC 2013
HashTable needs to calculate the power of two that is not less that the
This calculation used to be implemented as a relatively inefficient loop
(that's why the issue 7192942 was created).
The implementation was improved with
However it can be improved even more. I reused 7192942 number for this
Would you please help with reviewing?
Here's the webrev:
I also created a benchmark test to make sure the improvement is observable.
Here's the jmh benchmark I used:
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%.
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