[FFmpeg-devel] [PATCH] adpcm: Reset the ssd back to zero more often

Michael Niedermayer michaelni
Sat Nov 20 22:27:30 CET 2010

On Sat, Nov 20, 2010 at 08:59:25AM +0200, Martin Storsj? wrote:
> On Sat, 20 Nov 2010, Michael Niedermayer wrote:
> > On Thu, Nov 18, 2010 at 04:01:31PM +0200, Martin Storsjo wrote:
> > > If using very large trellis sizes (e.g. -trellis 15), the frontier
> > > is so large that the difference between the best and the worst
> > > trellis node in the frontier is large enough to cause wraparound.
> > > 
> > 
> > > Resetting at (1<<20) is enough to avoid the issue at -trellis 16
> > 
> > have you come to this conclusion by proof or by simply changing the
> > threshold and seeing no problems?
> By changing the threshold until there were no more problems with that 
> particular sample - sorry, I should have mentioned that.
> I think it can't be proven how often it needs to be reset. In the worst 
> pathological case, the best trellis node has ssd 0 while the worst one has 
> a ssd of 65535*65535 added in each generation, overflowing even if we'd 
> subtract the best node's ssd each round.
> The attached patch should avoid the issue properly regardless of how 
> pathologically bad case it is, giving a small but tolerable slowdown. Do 
> you think that is enough, or should that one be combined with this 
> previous patch, resetting it to 0 more often (or perhaps even every round) 
> to avoid this issue happening at all?

have you tried to change ssd to 64bit ?
maybe its faster

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