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

[Ivan Gerasimov]

On 30.07.2013 20:47, Aleksey Shipilev wrote:
> On 07/30/2013 07:35 PM, Ivan Gerasimov wrote:
>> 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>
> The nit: volatile writes are probably offset the results too much, it's
> better to use the explicit idiom to feed the values:
>
>      @GenerateMicroBenchmark
>      public void benchPowerOfTwoA(BlackHole bh) {
>          for (i = 0; i != MAX_I; ++i) {
>              bh.consume(roundUpToPowerOf2A(i));
>          }
>      }

Thanks, Aleksey!
Yes, this is much clearer. And shows much better improvement too :-)
Now it becomes ~45%.

Benchmark                                Mode Thr    Cnt Sec         
Mean   Mean error    Units
o.b.PowerOfTwoBench.benchPowerOfTwoA     avgt   1     20 5       
16.872        0.276  msec/op
o.b.PowerOfTwoBench.benchPowerOfTwoB     avgt   1     20 5        
9.304        0.378  msec/op

Sincerely yours,
Ivan

> -Aleksey.
>
>