RFR: 8282664: Unroll by hand StringUTF16 and StringLatin1 polynomial hash loops [v4]

[Ludovic Henry]

On Mon, 31 Oct 2022 22:06:20 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> 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.

@cl4es i can write the assembly and send it your way if you want

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PR: https://git.openjdk.org/jdk/pull/10847