[TribulationStaff]

In the case I have in mind, I want to do something by a method of halving, which means I need to work in iterations, and I don't want to overwrite the old steps, so I have configured my for loops such that with a gcd I could do that easily.

Other uses include finding the relative primacy, another way to determine parity, and there are countless recursive formulae which include a gcd.