Re: [Discuss-gnuradio] phase accumulator in gr_frequency_modulator_fc

[Brian Padalino]

2009/11/9 fangming he <address@hidden>:
>  Hi, All,
>
> I cannot understand why the phase accumulator should be limited to
> [-16*pi,16*pi]. Please clarify it for me if you have some ideas on it.
>
> The following is the code in this class:
>  if (fabs (d_phase) > 16 * M_PI){
>     double ii = trunc (d_phase / (2 * M_PI));
>     d_phase = d_phase - (ii * 2 * M_PI);
>   }

My guess is that there is still only so much precision in a floating
point number.  Knowing you are going to reduce the phase down modulo
2*pi, when dealing with large numbers, the error really starts to
accumulate.

Try it out.  Take a phase value and add 2*pi, then reduce that large
number down by 2*pi.  How many iterations does it take before you have
a significant error?

This is only a guess and by no means anything else.  If someone more
knowledgeable would like to shed some light, please do so.

Brian