Re: [FFmpeg-devel] [PATCH 2/3] checkasm/svqenc: add ssd_int8_vs_int16 test

[James Almer <jamrial@gmail.com>]

On 12/29/2023 9:16 AM, Martin Storsjö wrote:
> On Fri, 29 Dec 2023, flow gg wrote:
> 
>> Tests on x86 might fail, possibly due to a 16-bit sub overflow
> 
> If this only happens in checkasm but not in real life use, it means that 
> the checkasm test input is out of range, and we should try to mimic the 
> real input data.
> 
> If the issue is off-by-one due to rounding, we could allow it by making 
> a comparison per element, and tolerate a certain diff (maybe only on x86).
> 
> But if it is an actual overflow on valid input data, the x86 asm 
> definitely needs to be fixed, by someone... Worst case, we might want to 
> disable that checkasm test on x86 temporarily.

The function subtracts an int16 from an int8, whose result may not fit 
on an int16. The x86 asm expects it to do, hence the failures.

I don't know if such cases exist in real world files, so like you said, 
if they don't then the test should generate in-range input. But if they 
do, i'll fix the x86 asm (sadly, this means sse4 will be required 
instead of sse2).
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