RFC: inline assembly for alphablend functions

Hi,

xine's alphablend functions are terrible cpu hogs (in particular with hd
streams). I was wondering if it would be worthwile to improve things a
bit with simd instructions. I started with mem_blend32 because that's a
natural fit for mmx without touching anything else (and because this
itself uses a lot of time with yuy2 blending). Seems to work and reduce
executed instructions a lot though only on a K8 do I see any performance
improvement (the thing is once again heavily limited by memory
bandwidth). Of course it does exactly nothing unless you have
video.output.disable_exact_alphablend set. The code is also compiled and
executed unconditionally which obviously would need to change.
I guess there would be more of an improvement with the exact blend
function (looks a bit less limited by memory bandwidth) but that's
definitely much more work.
So what do you think?

Roland

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