The comments are informing the reader about the trick that turns npow2 into prevpow2. Your reply seems focused on npow2 itself, not the line npow2(x+1)/2 that I

The comments are informing the reader about the trick that turns npow2 into prevpow2. Your reply seems focused on npow2 itself, not the line npow2(x+1)/2 that I said deserves a comment. I agree that npow2 should have the tests and documentation that you say, but in my example I'm taking that function as given, eg. by a library.