Floating Point atan Megafunction

Not directly related to the atan() issue, but you could use the Goetzel generator to generate your sin (& cos) - uses the two previous values and a single multiply + add to get the next term. That would make it easier to change the frequency. Might just be a logic v memory tradeoff.

The atan() function will just be expanding one of the power series, if you have bounds on the input and desired accuracy it might be worth doing it yourself - when you can probably do it all as fixed point.