RFR: 8203352: Improve java implementation of Integer/Long.numberOfLeadingZeros

[Claes Redestad]

On 2018-05-18 20:23, Ivan Gerasimov wrote:
> Another approach may be to just delegate to 
> Integer.numberOfLeadingZeros() like this:
>
>     public static int numberOfLeadingZeros(long i) {
>         int x = (int)(i >>> 32);
>         return x == 0 ? 32 + Integer.numberOfLeadingZeros((int)i)
>                 : Integer.numberOfLeadingZeros(x);
>     }

I'm partial to the simplicity of this solution - whether or not there 
are platforms where 64-bit
lz instruction is missing. It's very slightly slower than baseline for 
-Xint, but markedly faster
when C1-compiled, which I think weighs heavier.

http://cr.openjdk.java.net/~redestad/8203352/open.01/

/Claes