Trig Functions In PicBasic
This topic has been discussed at length on StackOverflow, it is fairly processor-independent and language-independent except for the relative costs of multiplication/addition/lookup, which will make certain implementations more attractive.


How do Trigonometric Functions work?
Fast transcendent / trigonometric functions for Java
Trigonometric functions on embedded systems
How should I tackle ARCTAN...


The atan2() function, or rectangular-to-polar conversion, is not completely implementable by lookup tables of reasonable size; CORDIC is one option.