Arg! I fell asleep in my chair thinking about it.
I'm tellin' ya... I wrote a complement of 32bit math routines for my 6809E back in the day on my CoCo2. There's probably one friggin thing I'm forgetting. And no I haven't google'd anything because I don't want to.
I'll remember it eventually... Make that jab to the back of the head. Maybe that shot will knock it forward.