On Wed, Aug 10, 2022 at 2:53 PM Timo Rothenpieler <t...@rothenpieler.org> wrote:
> On 10.08.2022 23:43, Andreas Rheinhardt wrote: > > Timo Rothenpieler: > >> On 10.08.2022 23:24, Andreas Rheinhardt wrote: > >>> Timo Rothenpieler: > >>>> IEEE-754 differentiates two different kind of NaNs. > >>>> Quiet and Signaling ones. They are differentiated by the MSB of the > >>>> mantissa. > >>>> > >>>> For whatever reason, actual hardware conversion of half to single > always > >>>> sets the signaling bit to 1 if the mantissa is != 0, and to 0 if it's > 0. > >>>> So our code has to follow suite or fate-testing hardware float16 will > be > >>>> impossible. > >>> > >>> What does the exr spec say about quiet and signaling nans? > >> > >> Not sure how exr would be involved here. > > > > Your patch changes the output of an exr-test. The output of the exr > > decoder is presumably determined by the exr spec. There is after all the > > possibility that what hardware does in hardware and what this patch does > > in software is incompatible with what exr specifies. > > The exr spec just says something along the lines of analogous to > ieee-754 floats: > > https://openexr.readthedocs.io/en/latest/TechnicalIntroduction.html?highlight=ieee#the-half-data-type > It barely ever mentions NaNs, other than that they exist. Which makes > sense, given they don't typically appear in images. > > The only output changed is that for how NaNs are converted. > And given the cross-validation with multiple hardware implementations, > I'm confident that it's correct. > here is openexr implementation https://github.com/AcademySoftwareFoundation/Imath/blob/main/src/Imath/toFloat.cpp#L78 It has been a while since I check but I believe the current implementation matches this. The fate sample: rgb_scanline_zip_half_float_0x0_to_0xFFFF.exr was created to test this. it contains every possible float16 value > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
