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

[Joseph D. Darcy]

Hi Ivan,

On which platforms were the benchmark numbers collected?

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.
>