[FFmpeg-trac] #7124(swscale:reopened): Unexpected results from YUV-RGB color space conversion optimization on POWER8/LE

[FFmpeg]

#7124: Unexpected results from YUV-RGB color space conversion optimization on
POWER8/LE
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             Reporter:  seiko        |                    Owner:
                 Type:  defect       |                   Status:  reopened
             Priority:  normal       |                Component:  swscale
              Version:  git-master   |               Resolution:
             Keywords:  ppc altivec  |               Blocked By:
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  0            |
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Comment (by seiko):

 > Sorry, I realized that by now. Allow me to repeat that the original
 report was just invalid, post all necessary information including the
 command line you tested together with the complete, uncut console output
 here in the ticket, do not use external resources except for large source
 files.

 Sorry again, I just rushed into it and I thought that provide an external
 URL for the original report will be just enough since I only investigated
 on it just to clear OpenCV side, Thanks goes to Haitao Yue who actually
 discover it.
 ----


 >this is indeed a specific issue in libswscale.

 Yes, this how the frame looks like before disable optimization.
 [[Image(before.png, 100%)]]

 And here's after I disable PPC/yuv2rgb by using the patch in attachment.

 [[Image(after.png, 100%)]]

 I did a quick look into Altivec code on libswscale and I didn't realize
 any special cases for le or be and also you can easily realize many
 deprecated intrinsics on it, that why I said "current implementation of
 Altivec doesn't support little-endian".

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Ticket URL: <https://trac.ffmpeg.org/ticket/7124#comment:6>
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