multiplyHigh?

[Dmitrij]

Hi Andrew,

I support the idea of intrinsifying Math.multiplyHigh method: it seems 
like it will be very effective to implement at least on aarch64 and 
x86_64 using umulh and mulq instructions.

Vladimir, what do you think?


If there are no other volunteer I'd be happy to do this.

Enhancing java.lang.Math intrinsics situation for aarch64 port is on my 
todo list.

Thanks,
Dmitrij

On 08.09.2017 17:38, Andrew Haley wrote:
> I notice that Math.multiplyHigh(long, long) doesn't use a C2 intrinsic,
> even on machines with appropriate C2 patterns.  So it's rather slow.
>
> JDK-5100935, No way to access the 64-bit integer multiplication of
> 64-bit CPUs efficiently, is closed, even though there is still no
> efficient way to do this.  Is writing an intrinsic for multiplyHigh on
> someone's to-do list?  I see no bug for it.
>