Comment by andrepd

> There are likely several other optimizations related to cache locality that you could find in less time than it would take to do this, and those other optimizations would probably give several orders of magnitude more improvement.

How is cache / memory access relevant in a subroutine that performs a check on a 16bit number?

> Not to mention that the final code is basically a giant WTF for anybody reading it. It will be an attractive nuisance that people will be drawn to, like moths to a flame, any time there is a bug around calendar operations.

1: comments are your friend

2: a unit test can assert that this function is equivalent to the naive one in about half a millisecond.