[FFmpeg-devel] [PATCH 2/3] Indeo 5 decoder: common DSP functions

Michael Niedermayer michaelni
Sun Jan 17 20:02:53 CET 2010


On Sun, Jan 17, 2010 at 08:25:39PM +0200, Kostya wrote:
> On Sun, Jan 17, 2010 at 06:58:51PM +0100, Michael Niedermayer wrote:
> > On Sun, Jan 17, 2010 at 04:58:23PM +0200, Kostya wrote:
> [...]
> > >  
> > > It's not avoidable - this scaling cannot modify input since it's used
> > > for further decoding and output is uint8_t, so it is simply not enough
> > > for holding intermediate values.
> > 
> > static void horizontal_compose53i(IDWTELEM *b, int width){
> >     IDWTELEM temp[width];
> >             ^^^^^^^^^^^^^
> > this is avoidable
> 
> and some people will definitely ask you to avoid it because
> variable-length arrays are a bit controversial
>  
> > > In theory it should be faster, but unfortunately is not straight
> > > applicable here.
> > 
> > If we cannot merge the 2 5/3 wavelets then then optimizations would also
> > be duplicated (assuming there are volunteers for both) this feels like
> > a bad thing to me
> 
> Don't worry about volunteers - up to now we have neither for both :(
> IIRC, those two transforms also have inverted signs in lifting step too,
> which compilcates things a bit too.
> 
> > But if its really not possible then its not a reason to hold up indeo
> 
> Not without unpredictably serious changes to both codecs.

ok
also if someone else wants to take over reviewing of this patchset, that
would be welcome as iam quite busy with h264 optim and many other patches
and things currently

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Its not that you shouldnt use gotos but rather that you should write
readable code and code with gotos often but not always is less readable
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