[PATCH] x86-64: memcmp-avx2-movbe.S needs saturating subtraction [BZ #21662]

[Florian Weimer]

On 06/23/2017 10:48 PM, Richard Henderson wrote:
> On 06/23/2017 06:51 AM, Florian Weimer wrote:
>> +    shll    $8, %eax
>> +    shll    $8, %ecx
>>       bswap    %eax
>>       bswap    %ecx
>> +    movzbl    -1(%rdi, %rdx), %edi
>> +    movzbl    -1(%rsi, %rdx), %esi
>> +    orl    %edi, %eax
>> +    orl    %esi, %ecx
> 
> Do you really need to re-load and merge the final byte?
> It would appear you could leave the low byte zero.

Sorry, I don't understand.  Is this the same issue as H.J. raised and
improved?

The final/third byte certainly can affect the outcome of the comparison.

Thanks,
Florian