Clearly this bitwise stuff is harder than I originally thought! Good job the interwebs are full of people more brainy than me.

I'm going to have to sit down and have a long think about this stuff as my brain can't handle it right now, but I'm always like that first thing in the morning.

Thanks for your comment, and the time take to respond.

Thanks for the mention. Unfortunately, there's something fundamentally wrong with your article, and possibly with your understanding of how this works.

As I mention in my article, it's easy to get tricked into thinking binary OR (|) is equal to numerical addition (+), alas, it is not. The same goes for numerical subtraction (-), which is, well, &~ in bitwise operators, and a bit more advanced than simply doing OR and AND's.

Consider this:

F1 = 1<<1
F2 = 1<<2

mask = F1 # set the F1 flag

print mask + F1 # you get 4, which is, incorrect, F1 is already set.
print mask | F1 # you get 2, which is correct, F1 is already set.

You get the same results with subtraction:

mask = F1 | F2 # set both
print mask &~ F1 # 4, which is F2, correct.
print mask – F1 # 4, also “correct”, but,
print (mask – F1) – F1 # 2, oops.
print (mask &~ F1) &~ F1 # 4, correct, bit is already unset, second time has no effect.

You should revise your findings, as not understanding these things properly will cause significant flaws.

Hope this helps,