RFR 8203279 : Faster calculation of power of two

[David Holmes]

On 17/05/2018 1:01 PM, Ivan Gerasimov wrote:
> 
> 
> On 5/16/18 7:44 PM, David Holmes wrote:
>> On 17/05/2018 12:30 PM, Ivan Gerasimov wrote:
>>> Hi David!
>>>
>>>
>>> On 5/16/18 6:12 PM, David Holmes wrote:
>>>> Hi Ivan,
>>>>
>>>> Surely you need to back this up with some performance numbers! And 
>>>> verify not assume that numberOfLeadingZeroes is intrinsified!
>>>>
>>> Yes, good point.
>>> Please find the benchmark with the results here:
>>> http://cr.openjdk.java.net/~igerasim/8203279/00/MyBenchmark.java
>>>
>>> It shows that the new version of HashMap. tableSizeFor() was 
>>> (approximately) two times faster.
>>
>> Impressive. :)
>>
> Thanks :)
> Of course it's not performance critical code, but why not optimize it by 
> a tiny bit if possible?
> 
> Do you think it's good to go?

I think I'd rather defer to a more performance oriented reviewer - 
paging Claes! ;-)

David
-----

> 
> With kind regards,
> Ivan
> 
>> Thanks,
>> David
>>
>>> With kind regards,
>>> Ivan
>>>
>>>> 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.MIN_VALUE to Integer.MAX_VALUE (including), to make sure 
>>>>> the result is the same.
>>>>>
>>>>> For TimSort.ensureCapacity() I checked all positive values of 
>>>>> minCapacity.
>>>>>
>>>>
>>>
>>
>