Bug 3738 - libjpeg SIMD computing things wrong
Summary: libjpeg SIMD computing things wrong
Alias: None
Product: ThinLinc
Classification: Unclassified
Component: VNC (show other bugs)
Version: pre-1.0
Hardware: PC Unknown
: P2 Normal
Target Milestone: 4.10.0
Assignee: Peter Åstrand
Keywords: prosaic
Depends on:
Reported: 2011-02-07 09:47 CET by Pierre Ossman
Modified: 2019-02-26 10:25 CET (History)
0 users

See Also:
Acceptance Criteria:


Description Pierre Ossman cendio 2011-02-07 09:47:40 CET
Reported by DRC:

A user reported, and I reproduced, a severe accuracy problem in the
libjpeg-turbo fast integer forward DCT SIMD code that occurs only when
the JPEG quality is >= 98.  For these JPEG qualities, the SIMD version
of the code ceases to produce identical results to the non-SIMD version
of the code, which I consider to be a bug.

More info:

Further information on this:  I've narrowed down the problem to the
jsimd_quantize_sse2() and jsimd_quantize_mmx() functions in
jcqnts2i[-64].asm and jcqntmmx.asm, although I can't see any obvious
mathematical errors in that code.

And SF tracker entry:

Comment 1 Peter Åstrand cendio 2018-12-10 11:01:26 CET
This bug has been fixed upstream, and will be solved if we upgrade libjpeg-turbo.
Comment 2 Peter Åstrand cendio 2018-12-10 11:10:49 CET
(In reply to comment #1)
> This bug has been fixed upstream, and will be solved if we upgrade
> libjpeg-turbo.

Correction: This was fixed in 1.1.0 (ref: https://github.com/libjpeg-turbo/libjpeg-turbo/releases/tag/1.1.0) and we are using 1.5.3.
Comment 3 Pierre Ossman cendio 2018-12-11 12:56:07 CET
Nothing specific to test here, and we already did general testing of libjpeg during the upgrades.

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