[FFmpeg-devel] [PATCH] force dnxhd encoder to be independent of qsort internals

[Michael Niedermayer]

On Sun, Sep 20, 2009 at 11:39:26AM +0200, Reimar D?ffinger wrote:
> On Sun, Sep 20, 2009 at 11:08:45AM +0200, Reimar D?ffinger wrote:
> > On Sat, Sep 19, 2009 at 01:16:51PM +0200, Reimar D?ffinger wrote:
> > > this change makes sure there are no equal elements in the data passed to
> > > qsort, thus making sure the result is independent of implementation
> > > internals.
> > 
> > Very slightly different, swapped the mb comparison so the original order
> > is kept by default. Seems nicer and might decreases needed memory
> > bandwidth if a lot of values are identical (very unlikely I think).
> 
> qsort itself is nearly 5% slower for the Linux implementation:
> 31596660 dezicycles in encode_fast, 1 runs, 0 skips
> 30286580 dezicycles in encode_fast, 2 runs, 0 skips
> 29324712 dezicycles in encode_fast, 4 runs, 0 skips
> 28957121 dezicycles in encode_fast, 8 runs, 0 skips
> 28722058 dezicycles in encode_fast, 16 runs, 0 skips
> 28665462 dezicycles in encode_fast, 32 runs, 0 skips
> 28597622 dezicycles in encode_fast, 64 runs, 0 skips
> 
> 32579940 dezicycles in encode_fast, 1 runs, 0 skips
> 31456890 dezicycles in encode_fast, 2 runs, 0 skips
> 30567462 dezicycles in encode_fast, 4 runs, 0 skips
> 30156817 dezicycles in encode_fast, 8 runs, 0 skips
> 30013356 dezicycles in encode_fast, 16 runs, 0 skips
> 29935421 dezicycles in encode_fast, 32 runs, 0 skips
> 29924871 dezicycles in encode_fast, 64 runs, 0 skips
> 
> But difference for the whole encode_fast function is within the
> variance, at most 0.2 % slower I'd say as in this case (again,

why dont you just do a radix sort? Should only be a few lines
of C, faster and portable

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Observe your enemies, for they first find out your faults. -- Antisthenes
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