[Bug 773073] audioconvert: endian conversion optimization

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=773073

--- Comment #15 from Petr Kulhavy <brain at jikos.cz> ---
(In reply to Sebastian Dröge (slomo) from comment #5)
> > There are still two issues I'm trying to resolve:
> > 1) 24-bit does not compile in very efficient code. With -O3 it is 25% slower
> > than 32-bit and 45% slower than 16-bit. With -O2 it is 60% slower than both
> > 16-bit and 32-bit. So I'm trying to find an algorithm that gcc can optimize
> > better.
> 
> You might be able to get something more optimal if you unroll the loop. 4 *
> 24 bits are 3 * 32 bits, so the pattern of operations repeats every 4
> samples if you handle them as if they were 32 bit integers. Worth
> experimenting with that.

The 3*32 bits algorithm for the 24-bit conversion is better at -O2, but worse
at -O3. With -O2 it is 10% slower than the 32-bit conversion, which is OK. With
-O3 it is 60% slower than the 32-bit conversion - that's bad :-( 

So I will stay with the naive algorithm.

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