Re: [Sub-sonic-development] Interpolation figured out

[Lourens V. <js...@dd...>]

> For some reason I got the idea that in the module code I had been examining
> interpolation was a post process which doesn't make sense really, seeing as
> interpolation is about creating points.
> 
> I decided to re-exam what was going on and figured it out well and truely
> this time. What it does mean is that we 100% must go over the integer based
> mixing now, we cannot stick with floating point, there is no advantage and
> if it stays floating point our code will be extremely slow, I can easily see
> losses of several hundread percent.

That article is a bit misleading indeed! Glad my instinct was right
about this anyway (:

> Also it doesn't take long before you realise how well this code could work
> in assembler. The potential benefits are immense.

Yep. Looks dandy!

>The only problem in the above example is that SamplePos is moved by
>floating-point step, as F2/F1 is a floating-point value. To solve this, we
>can do simple linear interpolation, that is, separately add integral step
>and fractional step, like this: 

Huh? That is fixed point, has nothing to do with lerping, right?
 
> One final point and this is what I need you guys to help me on, see this
> line of code:
> 
> IntSamplePos += IntStep + CY;
> 
> CY from what I can work out represents the carry flag, it would appear this
> is something that isn't present in Windows compilers yet I believe you would
> find it in Borland compilers. I could really do with finding or simulating
> the carry counter (or maybe even the overflow flag) for my ANSI C++ part of
> SUB-SONIC. Once this is done I can actually get on and write the asm code
> and watch the CPU usage go down dramatically.

Well, I don't think you're going to get direct access to the carry flag
from ANSI C, after all there may not even be a carry flag on a certain
platform. Anyway, I suggest doing it the way you're doing it already,
add FracStep, and check if FracSamplePos is now smaller. If so,
increment IntSamplePos.

> So I hope I've cleared those points up for you (and me) now. I will play
> around with my mixing code a little more, it looks extremely ugly having two
> sorts of mixing code in the same module with 50% of commented out.

What happened to #ifdef?

> Doug

#Lourens