I did something similar for a high speed (10k rpm) stepper motor driver. We were emulating a legacy system and needed to do a 24 bit/16 bit divide, which took a

I did something similar for a high speed (10k rpm) stepper motor driver. We were emulating a legacy system and needed to do a 24 bit/16 bit divide, which took a long time. Even worse was that when the speeds increased, we had less time to do the computation. I came up with a trick: when the denominator changed to above a certain value, I knew the output's MSB would be zero, so I switched to a more efficient division routine that computed fewer bits. It was enough to get us smooth performance without running out of time.