[FFmpeg-devel] [PATCH] DES en-/decryption

[Michael Niedermayer]

Hi

On Mon, Oct 15, 2007 at 09:53:26AM +0200, Reimar D?ffinger wrote:
[...]
> > maybe
> > out |= P_shuffle2[ S_boxes2[i][tmp] ];
> > 
> > would be worth a try?
> > it would cut the needed table size down by 2 at the expense of one more
> > table lookup
> > (yes S_boxes2 would contain i so that P_shuffle2 could correctly reshuffle
> > it)
> 
> Well, I find it somewhat doubtful that adding a second table lookup to
> save 2kB (IIRC) makes sense without CONFIG_SMALL.

it could make sense if you consider that some CPUs have just a 8kb cache ...
anyway its just a random idea i dont know if its a good one ...


> 
> > [...]
> > 
> > > +    uint64_t CDn = shuffle(key, PC1_shuffle, sizeof(PC1_shuffle));
> > > +    // generate round keys
> > > +    for (i = 0; i < 16; i++) {
> > > +        CDn = key_shift_left(CDn);
> > > +        if (i > 1 && i != 8 && i != 15)
> > 
> > if((i&7) && i != 15)
> 
> This misses the i == 1 case, doesn't it?

yes ive missed that ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I do not agree with what you have to say, but I'll defend to the death your
right to say it. -- Voltaire
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