RFR: 8314124: RISC-V: implement Base64 intrinsic - decoding [v4]

[Hamlin Li]

On Tue, 27 Aug 2024 02:40:45 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> `(b1 | b2 | b3 | b4) < 0`, this java code is to tell if any of b1-b4 is < 0.
>> On the other side, `bltz(combined32Bits, Exit)` is doing the similar thing (same effect, but different way), as when loading byte1-4, `lb` will sign-extend it, if any of byte1-4 < 0, then the top bit will be 1, and after shift left, top bit will still be 1, so as a result, we can use combined32Bits to tell if any of byte1-4 < 0, and at the same time, we can use combined32Bits to decode the final data (from 4 bytes to 3 bytes). Or to put it another way, combined32Bits is constructed for 2 purposes at the same time.
>> Hope this answers your question?
>
> Yeah. Interesting. Could you please add a small code comment for this? Thanks.

Sure, added. Thanks!

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PR Review Comment: https://git.openjdk.org/jdk/pull/20026#discussion_r1732308194