RFR: 8316592: RISC-V: implement poly1305 intrinsic [v9]

[Hamlin Li]

On Fri, 10 Nov 2023 15:39:28 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> ArsenyBochkarev has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Rename poly1305-specific functions
>>  - Add final conditional reduce
>
> src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 4474:
> 
>> 4472: 
>> 4473:     __ srli(tmp1, U_2, 2);
>> 4474:     __ shadd(tmp1, tmp1, tmp1, tmp2, 2);
> 
> I'm afraid there might be an overflow issue here. 
> Consider a smplifed case(8 bits per U): U_2==0b11111111, tmp1 will be 0b111111, tmp1*5 will overflow, and there is carry for it.
> If I'm right, then the fix is to use 2 steps rather than one to reduce, please check the aarch64 version for details.

If the above issue is not a false one, and the implemention was tested with existing jdk test suite, then I'm afraid we need to add more test to catch this issue.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16417#discussion_r1389566035