How can I reverse optimized integer division/modulo by constant operations?

First Unfortunately we don't seem to have MathJax turned on in this stackexchange so the math parts below are pretty horribly formatted. I'm also far from a mathematician so the notation may be off in some places. Understanding the magic number and code The goal of the code above is to rewrite a division into a multiplication because division takes more clock cycles than a multiplication. It's in

[fcicq]

x * CON >> 32. CON = 2^32 / div