[Ffmpeg-devel] Re: [Ffmpeg-cvslog] r7570 - trunk/libavutil/fifo.c

[Michael Niedermayer]

Hi

On Thu, Jan 18, 2007 at 07:19:23PM -0800, Roman Shaposhnik wrote:
> Hi
> 
> On Fri, 2007-01-19 at 03:48 +0100, Michael Niedermayer wrote:
> > Hi
> > 
> > On Thu, Jan 18, 2007 at 04:41:21PM -0800, Roman Shaposhnik wrote:
> > [...]
> > > 
> > > > the extra if() also should disapear for av_fifo_read() if its inlined
> > > > and the body of the while loop will be executed just once normally
> > > > and rarely twice, but never more often then twice
> > > > 
> > > > do you know of any specific places in libav* where there are so many
> > > > calls to av_fifo_*read() that this could matter?
> > > 
> > >   Nope. All I care about is av_fifo_peek() ;-)
> > 
> > attached patch removes it and makes your code about 35% faster ;)
> 
>   Well, I had it coming ;-)

i knew you would like my suggestion ;)


> 
>   Now, the only problem I have with your approach is that you're
> exposing the guts of a Fifo implementation and that doesn't seem
> right to my OO-self. After all, that's what av_fifo_peek()
> was introduced for anyway. 

the problem i have (and had) with av_fifo_peek() is that it doesnt
solve the fifo-guts dependance it just hides it which IMHO is worse
people could use av_fifo_peek() and expect to have no dependance on the
fifo guts but they do, at the ABI level


> 
> > and i suspect it can be made even faster, of course this is not possible
> > with a av_fifo_peek like system
> 
>   You're right. However, I suspect that the most dramatic way of
> speeding it up would be to iterate over the fifo itself and shuffle
> at the frame level. We might also benefit from a precomputed reversed
> shuffling table (but most probably it wouldn't really matter since 
> it all fits into the cache anyway). I think it'll be the best
> of both worlds -- one wouldn't have to expose the guts yet the speed
> up will be there as well.
> 
>   Thoughts ?

iam happy with every solution which gets rid of fifo implementation
dependant code in fifo.h (and of course i strongly prefer solutions
implemented by others then myself as iam lazy ...)

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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