MotionFusion algorithms how is work?

Hy,
I m using MPU9150. I wonder how is work the MotionFusion algorithms , how is compute a euler angles, or quaternions. This is computed inside the chip ? This algorithm is hidden from users? so we can not know which filters,etc use this chip ?

I m using this library:
https://github.com/mlaurijsse/linux-mpu9150

thank you