Extracting Arducopter GNC

ArduCopter Copter 4.0
1

Hello,
I’m trying to understand Arducopter’s GNC (guidance navigation and control) algorithm, but i can’t find where it’s located in the code, nor where the current state of the drone is used.
Thanks for any help you can bring !

2

Here is a good starting point
https://ardupilot.org/dev/docs/apmcopter-code-overview.html