RFR: 8339992: RISC-V: some minor improvements of base64_vector_decode_round

[Hamlin Li]

On Wed, 18 Sep 2024 12:57:41 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Hi,
> Can you help to review this simple improvement?
> Thanks.

@RealFYang As we discussed previously, we're supposed to do following change too,
* `vsetvli(x0, failedIdx, Assembler::e8, lmul, Assembler::mu, Assembler::tu);` => remove mu/tu (i.e. change to ma/ta)

But after study the spec again, I can not find out the exact word supporting this change (maybe I missed it), so for safety consideration I will leave it as is.

If someone can find out the exact evidence in the spec that changing from mu/tu => mu/tu is absolutely safe on all devices, please kindly share your information, I'll add the change.

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PR Comment: https://git.openjdk.org/jdk/pull/21059#issuecomment-2358407204