Steve,
Yeah, that's Kahan summation (
https://en.wikipedia.org/wiki/Kahan_summation_algorithm ) to try and
minimize the floating point error. I'm not really sure it helps much there,
but I figured it can't hurt. I'm using kahan summation there specifically
because the fine timing estimate is summed over the entire processing
buffer instead of just over a symbol or two.
Thanks,
Brady OBrien
On Tue, Mar 22, 2016 at 3:06 AM, Steve <coupaydevi...@gmail.com> wrote:
> I had a question, maybe for Brady, on a calculation he does in fsk.c.
>
> In lines 1029 - 1036:
>
> https://sourceforge.net/p/freetel/code/HEAD/tree/codec2-dev/src/fsk.c#l1029
>
> you do a series of calculations.
>
> y.real = t1.real - c.real;
> y.imag = t1.imag - c.imag;
>
> t.real = t2.real + y.real;
> t.imag = t2.imag + y.imag;
>
> c.real = (t.real-t2.real) - y.real;
> c.imag = (t.imag-t2.imag) - y.imag;
>
> Rewriting 'c' (substituting 't') I get:
>
> c.real = ((t2.real + y.real) - t2.real) - y.real;
>
> I guess my question is, are you looking for floating point inaccuracy, and
> then subtracting any on the next loop?
>
> I was thinking, that otherwise 'c' would always be zero. I'm only on my
> first cup of joe though :-)
>
> 73,
> Steve
>
>
>
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