It will always be correct, but you can't just assume that the compiler will optimize the shifts into a byteswap instructions. If you look at the article you will see that it tires to no-true-scotsman that concern away by talking about a "good modern compiler".
And what exactly is the problem there? Are you going to be writing code that a) is built with a weird enough compiler that it fails this optimisation but also b) does byte swapping in a performance critical section?
