Comment by dmccarty

Great point, I wish I'd mentioned it. The expense of the printf dwarfs the log / log (double divided by a double then cast to an int), which itself is greater than some repeated comparisons in a for loop.

It's key to be able to recognize this when thinking about performant code.

In other words, the entire exercise is silliness because the eventual printf is going to blow away any nanoseconds of savings by a smarter/shorter routine.