flac dev - Jan 2005 - A couple of points about flac 1.1.1 on ppc/linux/altivec

I tried to send this message via gmane a couple of weeks ago but it never got
through moderation. So maybe the moderator is on holiday, or there is some
other problem in the gmane->flac-dev connection?

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Newsgroups: gmane.comp.audio.compression.flac.devel
Subject: A couple of points about flac 1.1.1 on ppc/linux/altivec
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From: John Steele Scott <toojays@toojays.net>
Date: Thu, 06 Jan 2005 17:14:12 +1030
Message-ID: <87fz1ff45f.fsf@fuzz.toojays.net>
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--- John Steele Scott <toojays@toojays.net> wrote:
> Back in October 2004, I did a bit of work on FLAC to get version
> 1.1.1 to
> build correctly under GNU/Linux/PPC. Only now have I realised that
> somewhere
> along the way something broke in FLAC's decoding. On my machine,
> roughly 50%
> of FLAC files are being decoded incorrectly.
> 
> I presume that I broke the code somehow when translating Josh's
> original OS X
> assembler into GNU style.
are you the one who submitted the patch with a translated
version of lpc_asm.s?  I thought that was Luca.
> Is there any kind of test harness or test routine which I could use
> to track
> down exactly where the problem lies?
no, that's one of the hardest things to debug.  you pretty much
have to single-step through it and making sense of it requires
intimate knowledge of the decoder.  that's why it takes me so
long to qualify any patches to the core encoder/decoder.  there
is little forgiveness from users for bugs in those.

Josh



		
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Josh Coalson <xflac@yahoo.com> writes:
> --- John Steele Scott <toojays@toojays.net> wrote:
>> Back in October 2004, I did a bit of work on FLAC to get version
>> 1.1.1 to
>> build correctly under GNU/Linux/PPC. Only now have I realised that
>> somewhere
>> along the way something broke in FLAC's decoding. On my machine,
>> roughly 50%
>> of FLAC files are being decoded incorrectly.
>> 
>> I presume that I broke the code somehow when translating Josh's
>> original OS X
>> assembler into GNU style.
>
> are you the one who submitted the patch with a translated
> version of lpc_asm.s?  I thought that was Luca.
I'm not sure exactly what happened. What you have in CVS:
<http://cvs.sourceforge.net/viewcvs.py/flac/flac/src/libFLAC/ppc/gas/lpc_asm.s?rev=1.1&view=log>

is not the same as the patch applied by Gentoo:
<http://www.gentoo.org/cgi-bin/viewcvs.cgi/media-libs/flac/files/flac-1.1.1-altivec.patch.gz>

There is little difference between either version except for the comment
style, and the way constant addresses are specified. Also the Gentoo patch
patches cpu.c, otherwise the Altivec code path isn't taken.

I'm trying to get a handle on where I should be looking to fix the problem.
If
your saying that the gas version in FLAC CVS has been validated, the easiest
solution is to just use that one. Otherwise I need to go back to the Apple
version. Presumably that one has been thouroughly checked?

cheers,

John
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