From: justliketomsthumbsblues@gmail.com   
      
   On Thursday, June 8, 2023 at 8:59:21 PM UTC-4, Tom Thumb wrote:   
   > On Thursday, June 8, 2023 at 7:17:06 AM UTC-4, Dirk Froehling wrote:    
   > > Am 02.06.23 um 19:15 schrieb Tom Thumb:    
   > > > On Thursday, June 1, 2023 at 8:33:08 PM UTC-4, Tom Thumb wrote:    
   > > >> On Thursday, June 1, 2023 at 2:05:06 PM UTC-4, stephen...@gmail.com   
   wrote:    
   > > >>> On Thursday, June 1, 2023 at 11:25:59 AM UTC-5, Tom Thumb wrote:    
   > > >>>> On Wednesday, May 31, 2023 at 3:17:30 PM UTC-4, Tom Thumb wrote:    
   > > >>>>> Mike Westerfield's "Toolbox Programming in C" contains a routine:    
   > > >>>>>    
   > > >>>>> void HandleControl (void)    
   > > >>>>> {    
   > > >>>>> if ((myEvent.wmTaskData4 & 0xFFFF8000) == 0)    
   > > >>>>> switch (myEvent.wmTaskData4) {    
   > > >>>>>    
   > > >>>>> ...    
   > > >>>>>    
   > > >>>>> I can find no explanation for doing this. I believe it's just   
   testing if any of the bits 17 - 31 have been set to one?    
   > > >>>>>    
   > > >>>>> I'd be grateful if someone would explain why this is being done. I   
   imagine I've missed something there or the IIgs Reference Manuals.    
   > > >>>> Oh, it's checking to see if wmTaskData4 is less than 32768    
   > > >>> Yes, that's correct. In this case wmTaskData4 holds a control ID   
   value, and all the control IDs that the code wants to check for are less than   
   32768. The "if" check is OK, but it's not really necessary, since the code   
   could just check for the    
   control IDs of interest via the "switch".    
   > > >>>    
   > > >>> I suspect the "if" check is there because the code was originally   
   written in Pascal for the Toolbox Programming in Pascal course and then later   
   translated to C. The "case" statement in ORCA/Pascal can only handle values up   
   to 32767, making a    
   check like this necessary, but the "switch" statement in C does not have the   
   same limitation.    
   > > >>>    
   > > >>> --    
   > > >>> Stephen Heumann    
   > > >> Ahh, thank you very much.    
   > > >    
   > > > May I ask though; why go about it this way: if ((myEvent.wmTaskData4 &   
   0xFFFF8000) == 0) rather than: if(myEvent.wmTaskData4 <= 32767) ?    
   > > >    
   > > > is there a reason? or just a choice?    
   > > >    
   > > It is easier to read. :)    
   > >    
   > > No, really. 32767 is meaningless in that context. wmTaskData4 contains a    
   > > bunch of seperate settings coded as bits, not a single number.    
   > >    
   > > 0xFFFF8000 is 1111 1111 1111 1111 1000 0000 0000 0000 in binary form,    
   > > and by ANDing wmTaskData4 with this number, you say "I am only    
   > > interested in the upper 17 bits, ignore the lower bits."    
   > > The IF condition then means "If none of the settings in the upper 17    
   > > bits is set, do the following."    
   > >    
   > > Dirk   
   > I get the ANDing to test if bits are set and that's what I thought first too   
   but as far as I've read the only thing wmTaskData4 ever contains is a zero or   
   a control id; it, wmTaskData4, isn't flags bits. Only after playing ANDing   
   that I stumbled upon    
   00000000000000001111111111111111, 0x7FFF, 32768 triggers that condition   
       
   >    
   > Was just wondering why.   
      
   He has a sense of humor. I think he was just messing with me.   
      
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