RFR: 8222029: Optimize Math.floorMod

Claes Redestad claes.redestad at oracle.com
Tue Apr 9 19:06:38 UTC 2019

In my cursory analysis of the test the interesting corner cases are
covered and I have no reason to believe we'd see spurious errors
elsewhere. I ran an adhoc semi-exhaustive test comparing results
of the new version with the old and got an all-pass.


On 2019-04-09 18:02, Joe Darcy wrote:
> Basically I'm inquiring about whether the existing tests provide at 
> least as good code coverage on the new implementation as the old one. As 
> it is a relatively simple method, perhaps it there is full coverage 
> before and after. However, at times changing the implementation requires 
> updates to the tests to includes different cases to check and I wanted 
> to make sure that was looked at here.
> Thanks,
> -Joe
> On 4/9/2019 5:32 AM, Claes Redestad wrote:
>> I think those tests cover all interesting corner cases, so the only way
>> I see it can be improved is to make it more exhaustive (say generate a
>> large random sample of tests every run). Do you feel that is needed?
>> /Claes
>> On 2019-04-09 01:35, Joseph D. Darcy wrote:
>>> Should any additional cases be added to 
>>> test/jdk/java/lang/Math/DivModTests.java to cover the new 
>>> implementation?
>>> Thanks,
>>> -Joe
>>> On 4/5/2019 10:21 AM, Claes Redestad wrote:
>>>> On 2019-04-05 17:41, Andrew Haley wrote:
>>>>> On 4/5/19 2:44 PM, Claes Redestad wrote:
>>>>>> Testing: tier1-2, all Math tests run locally, -prof perfasm 
>>>>>> verification
>>>>>> on the provided microbenchmark.
>>>>> Looks good.
>>>> Thanks!
>>>>> I've kicked the tyres on AArch64, and it looks like a useful 
>>>>> optimization. The
>>>>> gains when the divisor is constant (a common case) are modest but 
>>>>> worthwhile.
>>>> Thanks for trying it out and glad to hear it helps on AArch64 as well.
>>>> /Claes

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