Re: Announcing cdrskin-0.7.2
Hi,
> Why are the two logs added as integers (+) rather than
> as polynumials (^)? Why do you do % 255 rather than 256?
Interesting point.
The justification must be hidden in James S.
Plank's statement:
"This implementation makes use of the fact that
the inverse log of an integer is equal to the
inverse log of (i mod (2^w - 1))."
I'll try to find out why this is a fact and
why this causes the + in the multiplication
algorithm.
(Any hint appreciated. It is half a life ago
that i did sincere algebra.)
Nevertheless i think this open question does
not infringe the claim that ecma130ab.c
implements ECMA-130 Annex A by help of well
known mathematical methods.
> If you double the gfpow table's size you could
> elminate the % 255.
This is well worth a try.
I simplified the constant division by 3 but that
happens not often enough to have much effect.
One could also apply the division to the matrix
H which currently is an alter ego of the power
table.
The index computation of burn_rspc_q0q1()
can be done in part before the loop.
Maybe one would have to explore the route via
Fourier again for a really smart reformulation.
> Does ECMA provide any "test vectors" for you to test your code with?
> Unit tests might be very useful!
I test against the old implementation which was
once introduced by the founders of libburn.
Nevertheless i am not sure whether that one
really complies to ECMA-130.
A test would be to blow up some data sectors and
to burn them in raw mode. Then one would try to
read them as data blocks. The drive's decoder
would then deliver the original data if all went
right.
But for burning data sectors in raw mode there
are more things to learn. Some i find in the MMC
specs. Some are still obscure to me.
By the code replacement i just want to keep up
eventual old capabilities of libburn which i
had to remove after Joerg's intervention a few
weeks ago.
-------------------------------------------------
libburn does not stem from cdrtools.
It rather appears to have originated as academic
project which stalled when the semester was over.
When i began to beef it up, it became obvious
that its architecture was significantly more
elaborate than the implementation code in its
functions.
See also "Project history as far as known to me"
beginning in line 171 of
http://libburnia-project.org/browser/libburn/trunk/README
-------------------------------------------------
Have a nice day :)
Thomas
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