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


On 06/23/2017 06:38 PM, Carlos O'Donell wrote:

> I assume that this catches the regression by ensuring the high values of
> the subtraction result in an underflow which results in a positive value
> of the subtraction and a wrong answer?

Yes, I thought I said so in the commit message.

> Was this comment ever accurate? mobzwl is not a BE load.

We used bswap, so the register contents before the comparison is in
big-endian format.

>> +	orl	%edi, %eax
>> +	orl	%esi, %ecx
>> +	/* Subtraction is okay because the upper 8 bits a zero.  */
> 
> s/a zero/are zero/g

Okay, I'll fix this typo in a follow-up commit.

I won't work on the error → printf cleanup for now.  HJ asked that they
should be put into a separate commit.

Thanks,
Florian


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