Your mind is inventing the part about them doing it on a thursday afternoon before popping out to the pub.

This could have taken weeks of research and refinement. You can't tell from just looking at the final result.

Give yourself some credit. If you were tasked with producing a cosine implementation, you'd pull out some textbooks, read specs, research algorithms, try a few ideas, test, iterate. You could come up with this. The only reason you didn't is that you didn't need to make a cos function yet; you had other stuff to do.