[FFmpeg-devel] [PATCH] tests/fate/image: add a test for half-float dwab compressed stream

[James Almer]

On 5/6/2025 6:26 PM, Michael Niedermayer wrote:
> On Tue, May 06, 2025 at 06:10:22PM -0300, James Almer wrote:
>> On 5/6/2025 5:44 PM, Michael Niedermayer wrote:
>>> On Mon, May 05, 2025 at 04:44:06PM -0300, James Almer wrote:
>>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>>> ---
>>>>    tests/fate/image.mak                        | 3 +++
>>>>    tests/ref/fate/rgb-scanline-dwab-half-float | 6 ++++++
>>>>    2 files changed, 9 insertions(+)
>>>>    create mode 100644 tests/ref/fate/rgb-scanline-dwab-half-float
>>>>
>>>> diff --git a/tests/fate/image.mak b/tests/fate/image.mak
>>>> index 042cf6438f..abf204f69f 100644
>>>> --- a/tests/fate/image.mak
>>>> +++ b/tests/fate/image.mak
>>>> @@ -124,6 +124,9 @@ fate-exr-rgb-scanline-pxr24-float-12x8: CMD = framecrc -i $(TARGET_SAMPLES)/exr/
>>>>    FATE_EXR += fate-exr-rgba-multiscanline-half-b44
>>>>    fate-exr-rgba-multiscanline-half-b44: CMD = framecrc -i $(TARGET_SAMPLES)/exr/rgba_multiscanline_half_b44.exr -vf scale -pix_fmt gbrapf32le
>>>> +FATE_EXR += fate-rgb-scanline-dwab-half-float
>>>> +fate-rgb-scanline-dwab-half-float: CMD = framecrc -i $(TARGET_SAMPLES)/exr/rgb_scanline_dwab_half_float.exr -vf scale -pix_fmt gbrpf32le
>>>> +
>>>>    FATE_EXR += fate-exr-rgb-scanline-float-b44
>>>>    fate-exr-rgb-scanline-float-b44: CMD = framecrc -i $(TARGET_SAMPLES)/exr/rgb_scanline_float_b44.exr -vf scale -pix_fmt gbrpf32le
>>>> diff --git a/tests/ref/fate/rgb-scanline-dwab-half-float b/tests/ref/fate/rgb-scanline-dwab-half-float
>>>> new file mode 100644
>>>> index 0000000000..a5a1997785
>>>> --- /dev/null
>>>> +++ b/tests/ref/fate/rgb-scanline-dwab-half-float
>>>> @@ -0,0 +1,6 @@
>>>> +#tb 0: 1/25
>>>> +#media_type 0: video
>>>> +#codec_id 0: rawvideo
>>>> +#dimensions 0: 512x512
>>>> +#sar 0: 1/1
>>>> +0,          0,          0,        1,  3145728, 0xbb11b00a
>>>
>>> differnt result here: (on linux x86-64)
>>>
>>> --- ./tests/ref/fate/rgb-scanline-dwab-half-float	2025-05-06 22:40:40.017406113 +0200
>>> +++ tests/data/fate/rgb-scanline-dwab-half-float	2025-05-06 22:40:53.297513198 +0200
>>> @@ -3,4 +3,4 @@
>>>    #codec_id 0: rawvideo
>>>    #dimensions 0: 512x512
>>>    #sar 0: 1/1
>>> -0,          0,          0,        1,  3145728, 0xbb11b00a
>>> +0,          0,          0,        1,  3145728, 0x2a15f7aa
>>> Test rgb-scanline-dwab-half-float failed. Look at tests/data/fate/rgb-scanline-dwab-half-float.err for details.
>>
>> Yeah, I can reproduce it, and even if i add "sws_flags
>> +accurate_rnd+bitexact" i get the same results (0xbb11b00a on Win64,
>> 0x2a15f7aa on Linux x86-64). I also get a different hash in both targets if
>> i don't rescale to gbrpf32, so the problem is not in swscale.
>>
>> Neither Valgrind or gcc-usan complain, so I'm not sure what could be
>> producing this difference.
> 
> float is not bitexact in C, and float on x86 might use old x87 style while
> x86-64 might be SSE*/AVX, so if theres any float in the code slight differences
> can happen, no idea if half float in this case is affected by this or not
x87 float instructions are not used in x86_64, which is both these 
targets. For float16 it will either use CPU instructions if available, 
or the fallback we have using a lookup table (through float2half and 
half2float).

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