On Wed, 19 Feb 2003, Jaroslaw Sobierski wrote:
> Quoting Jaroslav Kysela <[EMAIL PROTECTED]>:
> >
> > I've implemented the whole transfer and mix loop in assembly and it works
> > without any drastic impact on CPU usage. I tried to optimize the assembler
> > part as much as I can, but if some assembler guru want to give a glance,
> > I'll appreciate it. The function is named mix_areas1() in
> > alsa-lib/src/pcm/pcm_dmix.c.
> >
>
> It seems to me it would make sens to code it for mmx (to use the saturation
> it offers for example). If you go for pure 386 there's little to win.
Yes and no. I don't think that there will be enough need for the
saturations, so the saturation code path mostly takes 4 instructions (two
compare, two skipped conditional jumps).
> Did you look at the assembly generated by gcc when compiling with
> optimiazations? I usually make this a start point when moving time-critical
Yes, my code is based on the code from GCC.
> code to assembly, and if it looks optimized enough - I leave it at that,
> unless I can use tricks not available to the compiler - like, again, mmx.
>
> I don't know how well gcc is optimized for intels, but I remember that you
> really had to work your ass of to beat inner loops optimized by Watcomm
> compilers (BTW I heard they're coming back with open source compilers :-).
> Not to mention proprietary Intel compilers which can take into
> account things like word alignment for data and code, cache hit / miss
> situations, branch preditiction and all kinds of magical stuff.
Yes, of course. I've not claimed that I wrote the best code in the world ;-)
But something we can start with.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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