[vorbis-dev] OGG header

[Segher Boessenkool]

Keith Wright wrote:
> 
> > From: Segher Boessenkool <segher at chello.nl>
> >
> > Sorry for taking so long to answer this one...
> 
> Thank you for taking the time to answer at all.

You're welcome.

> 
> > Say your CRC polynomial P(X) has deg N (in our case, N is 32);
> > P(X) is irreducible over F_2[X], so there is a natural mapping
> 
> I haven't checked the algebra yet, but the end result seems to
> be that this is not a bug, it is deliberate and there is a theory

Mathematically, there's no big difference.  Practically, you want to
shift all bits fully through the "shift register" at least once.
Computationally, there's the question of what algo is faster.

> behind it.  If I can work through the details, I will write it
> up and post it somewhere.

There's textbooks full of this stuff, I think...

> 
> > p.s. Yes I know I'm off-topic :)
> 
> Oh, oh.  If the answer is off-topic then the question
> must have been off-topic, but unless I have misunderstood
> the purpose of vorbis-dev, I don't see how a discussion
> of an algorithm used in Vorbis and possible bug report
> could be off-topic (trival or wrong, yes, off-topic, no).
> 
> Or is it off-topic because it is an Ogg algorithm rather
> than a Vorbis algorithm?

It is off-topic because Ogg just uses some well-known results;
it never touches on any of the acctual theory behind it.

Things like "open your files with "rb" " are off-topic too,
in the same way, imho.

<p>Cheers,

Segher
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