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From: castong@bucsb.UUCP (Paul Castonguay)
Newsgroups: comp.sys.amiga.tech
Subject: Re: A bug in ARP 1.3?
Message-ID: <148@bucsb.UUCP>
Date: 12 Dec 89 23:02:06 GMT
References: <14752@boulder.Colorado.EDU> <3598@jhunix.HCF.JHU.EDU>
Reply-To: castong@bucsb.bu.edu (paul castonguay)
Followup-To: comp.sys.amiga.tech
Distribution: na
Organization: Boston Univ Comp. Sci.
Lines: 17

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?

                                  -Paul Castonguay