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

["Martin Storsjö" <martin@martin.st>]

On Fri, 29 Dec 2023, James Almer wrote:

> 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).

I think it's probably best to limit the checkasm inputs that don't 
overflow, for now.

// Martin
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