RFR: JDK-8216437 : PPC64: Add intrinsic for GHASH algorithm [v28]

[Suchismith Roy]

On Fri, 28 Feb 2025 16:30:16 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Suchismith Roy has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   use vsplitsb
>
> src/hotspot/cpu/ppc/stubGenerator_ppc.cpp line 574:
> 
>> 572:     masm->vsldoi(vLowProduct, vLowProduct, vLowProduct, 8);           // Swap
>> 573:     masm->vxor(vLowProduct, vLowProduct, vReducedLow);                // Reduction using constant
>> 574:     masm->vsldoi(vCombinedResult, vLowProduct, vLowProduct, 8);       // Swap
> 
> The part between the vpsumd instructions looks too complicated. Isn't it equivalent to the following?
> 
>     masm->vsldoi(vTmp8, vLowProduct, vHighProduct, 8);
>     masm->vsldoi(vTmp9, vReducedLow, vReducedLow, 8);
>     masm->vxor(vTmp8, vTmp8, vMidProduct);
>     masm->vxor(vCombinedResult, vTmp8, vTmp9);

@TheRealMDoerr can you explain how it can be equivalent to these 4 instructions ? 
we are  extracting the different parts of midProduct here ,64 bits each, for the cross product. 
I,e Xl * Hh +Hl*Xh , so the below 2 are required 
masm->vsldoi(vTmp8, vMidProduct, vZero, 8);                      
masm->vsldoi(vTmp9, vZero, vMidProduct, 8);     
    



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PR Review Comment: https://git.openjdk.org/jdk/pull/20235#discussion_r1976673259