Often we use microcontrollers to do things in our robots, but need to make some calculations in decimal. Using floating point variables is very slow, because a software floating point library is automatically included (unless you have a high-end microcontroller). Therefore, we generally use fixed point arithmetic.
Whenever I do this, I just use an integer, and remember where the decimal place is. However, it does take some care to ensure that everything is consistent, especially when calculations involve variables where the decimal point is in a different place.
I have implemented a fixed point atan2 function, but because I was trying to squeeze every last drop of limited precision (16 bits), I would often change the definition of where the decimal point is, and it would change as I tweaked it. In addition, I would have some constants, as a quasi look-up table, which themselves have an implied decimal point somewhere.
I want to know if there is a better way. Is there a library, or set of macros, that can simplify the use of fixed point variables, making multiplication and division between mixed variables easier, and allowing declaration of decimal numbers or constant expressions, but automatically converting to the desired fixed point representation at compile time?