Re: Re: dmix plugin

[Abramo Bagnara <abramo.bagnara@libero.it>]

Jaroslaw Sobierski wrote:
> 
> Quoting Abramo Bagnara <abramo.bagnara@libero.it>:
> >
> > The results are amazing and I'd say Jaroslav has done some mistakes in
> > his handmade asm.
> >
> 
> This may be true, but I think you're trying to be a little too quick yourself.

No doubts about that, I was in a hurry.

> Did you *test* your code? I only had time to take a short glance at it, but
> too me it seems that this is not the correct check for overflow on signed
> numbers:
> 
> >                       if (unlikely(sample & 0xffff0000))
> >                                s = sample > 0 ? 0x7fff : -0x8000;
> >                        else
> >                                s = sample;
> 
> I noticed it because this is the first thought I had, but it only works
> for unsgined. Notice that -1 will be 0xffffffff in a 32 bit sample. So
> your code will "saturate" all negative samples to -8000 effectively
> killing half of the wave, the way a diode does. I'm pretty sure this
> would not sound good ;-). Still, even if you change this to two normal
> ifs I assume the speed will not be affected by an order of magnitude.
> 
> Secondly, the test code is hardly a good representation of our "working"
> environment because we're expecting multiple processes to write
> concurrently to the buffer. I think you sholud have a "verification"
> procedure which carefully mixes the waves one by one and then the
> n test mixes should be run in m processes concurrently. And the result
> compared to the "verification" table.

This is best tested with an SMP machine and I've not an easy access to
it.

That's apart you're perfectly right and this was exactly my intentions.

-- 
Abramo Bagnara                       mailto:abramo.bagnara@libero.it

Opera Unica                          Phone: +39.546.656023
Via Emilia Interna, 140
48014 Castel Bolognese (RA) - Italy


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