RFR 8209171 : Simplify Java implementation of Integer/Long.numberOfTrailingZeros()

[Ivan Gerasimov]

Hi Joe!


On 8/9/18 4:20 PM, Joseph D. Darcy wrote:
> Hi Ivan,
>
> On which platforms were the benchmark numbers collected?
>
Ah, yes, should have mentioned that.
macOS 10.13.5 High Sierra, processor 3.1 GHz Intel Core i7

With kind regards,
Ivan

> Thanks,
>
> -Joe
>
> On 8/9/2018 4:15 PM, Ivan Gerasimov wrote:
>> Hello!
>>
>> Integer.numberOfTrailingZeros() and Long.numberOfTrailingZeros() are 
>> intrinsified by Hotspot, so the Java implementation of these is not 
>> too important.
>> However, they still can be improved by a tiny bit :)
>>
>> Could you please help review the fix?
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8209171
>> Webrev: http://cr.openjdk.java.net/~igerasim/8209171/00/webrev/
>> Benchmark for Integer: 
>> http://cr.openjdk.java.net/~igerasim/8209171/00/bench/int/MyBenchmark.java
>> Benchmark for Long: 
>> http://cr.openjdk.java.net/~igerasim/8209171/00/bench/long/MyBenchmark.java
>>
>> The resulting code is both smaller and faster.  It may also help to 
>> warm up Integer.numberOfLeadingZeros() quicker.
>>
>> On average, the new Integer.numberOfTrailingZeros() has got +11% to 
>> performance for -client and +1% for -server.
>> Long.numberOfTrailingZeros() is faster on 17% for -client and +20% 
>> for -server.
>>
>
>

-- 
With kind regards,
Ivan Gerasimov