🚀 go-pugleaf

> What does the following line mean?
>
>     Wait(1 << Window->UserPort->mp_SigBit)
>
> I know it causes my program to wait for a response in the IDCMP port,
> but how exactly does this work?
>
> ->  means structure member notation for pointers
>
> <<  means shift left, a bitwise operator, which can also be enterpreted
>    as multiplication by 2
>
> So, why should shifting the mp_SigBit member of the window's UserPort
>  One bit position to the left magically cause my application to wake up 
> from a sleeping condition and recognize the presence of an incoming message?


It doesn't. The   << (and >>)  C operators mean 

	a << b

Shift a left by b bit positions.  (shift right for >> )

So  Wait(1 << Window->UserPort->mp_SigBit)

means shift a 1 left to the position corresponding to the signal number.
So for example
an  mp_SigBit of 3 coresponds to a bit mask of  binary  1000 (i.e. bit
position 3).

Wait needs a bit mask, while mp_SigBit is the signal number.

>                                 -Paul Castonguay


John Guineau