Mail Archives: pgcc/1999/07/06/06:18:04
On Mon, 5 Jul 1999, Marc Lehmann wrote:
> On Fri, Jul 02, 1999 at 07:51:22PM +0200, Niteshadow wrote:
> > I just downloaded the bladeenc 0.81 sources and tried to tweak it
> > to the max. Well... tried... for some reason when I changed the original
> > - -O1 in the make rule for codec.o to -O2, the bladeenc started to create
> > MP3s with DIFFERENT data (compared using md5sum). I tried it only at work
> > on a Celeron 300A/128MB Ram/PGCC 1.1.3/Linux Mandrake 6.0/kernel 2.2.10
> > Options like -mpentiumpro, -malign-double, -march=pentiumpro did
> > not cause this to happen. Could anyone give me a clue about what could
> > cause this kind of ``feature'' ???
>
> Dumb question: were the resulting streams correct? Rounding differences are
> something you might expect (doesn't bladeenc use -ffast-math by default?)
I do not know, whether the streams where correct. I was just trying to
find out, whether the documentation was correct (it said something about
gcc corrupting the output stream), since I thought this could not happen,
if you use the _right_ optimisations.
I am walking on thin ice here.. I do not think, that specifying -O2 should
introduce rounding errors, but I am not all-too familiar with the way
compiler does all optimisations. Yet I think that as long as one does NOT
specify -ffast-math (which bladeenc doesn't), there should not be any
round-ff errors introduced by any of the optimisation options.
The implicit compiler-options for bladeenc are:
for the codec engine:
-O1
for the rest of code:
-O2 -malign-loops=2 -malign-jumps=2 -funroll-all-loops
>
> --
> -----==- |
> ----==-- _ |
> ---==---(_)__ __ ____ __ Marc Lehmann +--
> --==---/ / _ \/ // /\ \/ / pcg AT goof DOT com |e|
> -=====/_/_//_/\_,_/ /_/\_\ XX11-RIPE --+
> The choice of a GNU generation |
> |
>
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From : Robert 'Niteshadow' Varga
email : niteshadow AT hq DOT alert DOT sk, varga AT ibl DOT sk
PGPkey: http://hq.alert.sk/~niteshadow/pgpkey.txt
phone : +421 903 511 985 (mobile, always), +421 863 432 49 75 (home, rarely)
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