I already posted these in my ongoing thread about oldskool graphics programming, but I think these particular two parts are more at home here:
http://scalibq.wordpress.com/2013/03/20/just-keeping-it-real-part-10/
http://scalibq.wordpress.com/2013/03/24/just-keeping-it-real-part-10-1/

If you want to perform advanced arithmetic on an early 8-bit machine, these articles will teach you how to implement mul and div in software, and how to extend the precision of arithmetic operations from 8-bit to arbitrary precision.
Or if you're just interested in reading about the maths involved, that's fine as well :)
Posted on 2013-03-25 10:28:55 by Scali