[FFmpeg-devel] [PATCH v2 2/2] random_seed: Improve behaviour with small timer increments with high precision timers

[Michael Niedermayer]

Hi Martin

On Wed, Feb 12, 2025 at 11:25:03AM +0200, Martin Storsjö wrote:
[...]
> > Heres an example where the SWAP is needed:
> >     noswap swap
> > 5 -> [x 5]  [x 5]
> > 4 -> [5 4]  [5 4]
> > 5 -> [5 4]  [4 5]
> > 6 -> [4 6]  [5 6]
> > 5 -> [6 5]  [6 5]
> > 
> > In the last case the 5 is in the old* when the swap was used but not
> > when it was not used
> 
> Sorry, but your examples do not make sense or do not contain enough context
> (it does not include the initial states of the two old values, and it
> requires guesswork which ones of the two [x y] values is old and which one
> is old2).
> 
> But to be clear:
> 
> Please specify the initial values of the variables new, old and old2, for a
> case where
> 
> > > if (old2 == new) {
> > >     FFSWAP(old,old2);
> > > } else if (old != new) {
> > >     old2 = old;
> > >     old = new;
> > > }
> 
> produces a different end result than
> 
> > > if (old != new) {
> > >     old2 = old;
> > >     old = new;
> > > }
> 
> I claim that for any values of these variables, the end result is the same.

yes, you are correct, i thought you intended to run the old2/old update only if
new differs from both old and old2.

The actual code you wrote is fine and nicely optimizes the swap out

thx

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

The worst form of inequality is to try to make unequal things equal.
-- Aristotle
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