On Mon, 31 Oct 2022 13:35:36 GMT, Quan Anh Mai <qa...@openjdk.org> wrote:
>> But doing it forward requires a `reduceLane` on each iteration. It's faster
>> to do it backward.
>
> No you don't need to, the vector loop can be calculated as:
>
> IntVector accumulation = IntVector.zero(INT_SPECIES);
> for (int i = 0; i < bound; i += INT_SPECIES.length()) {
> IntVector current = IntVector.load(INT_SPECIES, array, i);
> accumulation =
> accumulation.mul(31**(INT_SPECIES.length())).add(current);
> }
> return accumulation.mul(IntVector.of(31**INT_SPECIES.length() - 1, ...,
> 31**2, 31, 1).reduce(ADD);
>
> Each iteration only requires a multiplication and an addition. The weight of
> lanes can be calculated just before the reduction operation.
Ok, I can try rewriting as @merykitty suggests and compare. I'm running out of
time to spend on this right now, though, so I sort of hope we can do this
experiment as a follow-up RFE.
-------------
PR: https://git.openjdk.org/jdk/pull/10847
