Dummond D. Slow (mental.delete@this.protozoa.us) on November 18, 2020 9:21 am wrote:
> Maynard Handley (name99.delete@this.name99.org) on November 18, 2020 9:13 am wrote:
> >
> > x264 in SPEC is not there to help you decide which PC to buy for ripping DVD content!
> > It is there as an exemplar of certain styles of code: various generic compression techniques
> > (so lots of bit by bit manipulation) and various image analysis techniques (so searches
> > over images and image comparisons at various frequency granularities).
> >
>
> You didn't read it? If x264 is example of a kind of code, it is an example of code
> heavily optimised with multimedia (integer) SIMD. It's a greeat example or maybe
> too great, other codebases like ffmpeg or x265 will be a bit less optimized.
>
> If you want to explore such code, run it with assembly. It has assembly for ARM too, and not that
> little of it. Without SIMD, it is the opposite of example of multimedia compression code.

You do realise that many of the key loops are autovectorized right? Yes it's probably not quite as fast as handwritten libraries, but it runs much faster with vectorization enabled.

Wilco