I'm currently using Microchip's Fixed Point Library, but I think this applies to most fixed point libraries. It supports Q15 and Q15.16 types, respectively 16-bit and 32-bit data.
One thing I noticed is that it does not include add, subtract, multiply or divide functions.
How am I supposed to do these? Is it as simple as just adding/subtracting/multiplying/dividing them together using integer math? I can see addition and subtraction working, but multiplying or dividing wouldn't take care of the fractional part...?
It turns out that all basic arithmetic functions are performed by using the native operators due to how the numbers are represented. e.g. divide uses the / operator and multiply the * operator, and these compile to simple 32-bit divides and multiplies.