TweetFollow Us on Twitter

AppleEvents 101 Bug
Volume Number:9
Issue Number:7
Column Tag:Article Rebuttal

Related Info: Notification Mgr Event Manager Apple Event Mgr

Apple Events 101 Bug

Bit Mask vs. Bit Number

By John Theisen, Flagstaff, Arizona

About the author

John Theisen, Macintosh Developer

1000 W. Forest Meadows #262, Flagstaff, AZ 86001 USA INTERNET:

Dear Sirs,

This letter is in response to the writer of AppleEvents 101 in your May 1993 Issue of MacTech Magazine.

While debugging the code that I had entered I came across a few problems with Dr. Kane's InitMac() routine. His painstaking use of the Gestalt Manager to determine the environment that the application is functioning in was done without a flaw, UNTIL he tests for the PPC attributes.

Dr Kane's code reads as follows:

 if (BitTest(&response, gestaltPPCSupportsRealTime) != 0)
 theErr = PPCInit();
 // if this bit is not set, we need to initialize

OK this looks to be correct given the previous calls to Gestalt() and then the testing of the attributes. Apple Inside Macintosh, Volume VI, Using the PPC Toolbox (page 7-10) specifical states that testing for the gestaltPPCSupportsRealTime should be conducted in the following manner:


 err := Gestalt(gestaltPPCToolboxAttr, PPCAttributes);
 IF err = noErr
 THEN {PPC Toolbox is present}
 IF BAND(PPCAttributes, gestaltPPCSupportsRealTime)=0
 {INIT PPC Toolbox HERE}

This shows that in order to test for the gestaltPPCSupportsRealTime we are using a Binary AND ... this is *NOT* the same as a BitTest operation.

I have substituted the following code which matches more closely with Apple's version:

/* 2 */

 if ((response & gestaltPPCSupportsRealTime) == 0)
 theErr = PPCInit();
 // if this bit is not set, we need to initialize

 if ((response & gestaltPPCSupportsOutGoing) == 0);
 // tell the user to turn on AppleTalk
 if ((response & gestaltPPCSupportsIncoming) == 0);
 // tell the user to activate file sharing or Appletalk

For clarification of the BTST operation in the BitTest() procedure provided by Dr. 
Kane I am quoting the Motorola M68000 Programmer's Reference Manual

 "BTST  Test a Bit
A bit in the destination operand is tested, and the state of the specified bit is reflected 
in the Z condition code.  If a data register is the destination, then the bit number is modulo 
32, allowing bit manipulation on all bits in a data register..."
The PPC constants are defined as:

/* 3 */

gestaltPPCToolboxPresent = 0x0000
/* PPC Toolbox is present. Requires PPCInit to be called */

gestaltPPCSupportsRealTime = 0x1000
/* PPC Supports real-time delivery */

gestaltPPCSupportsIncoming = 0x0001
/* PPC will deny incoming network requests */

gestaltPPCSupportsOutGoing = 0x0002
/* PPC will deny outgoing network requests */

[taken from GestaltEqu.h Copyright Apple Computer, Inc. 1988-1990]

In the code originally supplied, we would be testing BIT 4096 (and since 4096 MOD 32 = 0, the code would test BIT 0). This happens to be the bit indicating that the PPC Toolbox is present.

The cases for gestaltPPCSupportsIncoming and gestaltPPCSupportsOutGoing read much the same as the above case for gestaltPPCSupportsRealTime. If used with the BitTest() operation gestaltPPCSupportsIncoming will test BIT 1 instead of BIT 0 (0x0001 in binary has BIT 0 set not BIT 1) and gestaltPPCSupportsOutGoing is also off by 1, testing BIT 2 instead of BIT 1.

When testing for these PPC toolbox attributes, Apple requires that you use these as bit masks and NOT bit numbers. Although your code may check out fine in the testing phase, these lurking bugs will come back to haunt you.

I hope that some other Developers can find this information useful. As a side note, users who wish to notify the user of the AE101 application that they need to turn on Appletalk in the Chooser should notice that the initialization of the Dialog Manager as well as a few other key managers should take place before they try to place any dialogs on the screen.

John Theisen

Macintosh Developer

NOTE Published in Editorial, August 1993:


Jeff Kane wrote one of our most successful articles - AppleEvents 101 in the May ‘93 issue. We printed a rebuttal to his article that turned out not to be his bug. Evidently, Apple changed the header files and as a result, the definition of the gestaltPPC constants. Sorry Jeff.


Community Search:
MacTech Search:

Software Updates via MacUpdate

Cocktail 11.5 - General maintenance and...
Cocktail is a general purpose utility for macOS that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Backup and Sync 3.40.8921.5350 - File ba...
Backup and Sync (was Google Drive) is a place where you can create, share, collaborate, and keep all of your stuff. Whether you're working with a friend on a joint research project, planning a... Read more
Skype - Voice-over-internet pho...
Skype allows you to talk to friends, family, and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
Hazel 4.2.4 - Create rules for organizin...
Hazel is your personal housekeeper, organizing and cleaning folders based on rules you define. Hazel can also manage your trash and uninstall your applications. Organize your files using a familiar... Read more
ForkLift 3.2 - Powerful file manager: FT...
ForkLift is a powerful file manager and ferociously fast FTP client clothed in a clean and versatile UI that offers the combination of absolute simplicity and raw power expected from a well-executed... Read more
ScreenFlow 7.3 - Create screen recording...
ScreenFlow is powerful, easy-to-use screencasting software for the Mac. With ScreenFlow you can record the contents of your entire monitor while also capturing your video camera, microphone and your... Read more
Time Out 2.4 - Break reminder tool with...
Time Out helps remind you to take work breaks throughout the day. It has two kinds of breaks: a "Normal" break, typically for 10 minutes after 50 minutes of work, so you can move about and relax,... Read more
Smultron 10.1.3 - Easy-to-use, powerful...
Smultron 10 is an elegant and powerful text editor that is easy to use. You can use Smultron 10 to create or edit any text document. Everything from a web page, a note or a script to any single piece... Read more
Tor Browser Bundle 7.5.2 - Anonymize Web...
The Tor Browser Bundle is an easy-to-use portable package of Tor, Vidalia, Torbutton, and a Firefox fork preconfigured to work together out of the box. It contains a modified copy of Firefox that... Read more
Yummy FTP Pro 2.0.3 - $29.99
Yummy FTP Pro is an advanced Mac file transfer app which provides a full-featured professional toolkit combined with blazing speeds and impeccable reliability, so whether you want to transfer a few... Read more

Latest Forum Discussions

See All

How PUBG, Fortnite, and the battle royal...
The history of the battle royale genre isn't a long one. While the nascent parts of the experience have existed ever since players first started killing one another online, it's really only in the past six years that the genre has coalesced into... | Read more »
Around the Empire: What have you missed...
Oh hi nice reader, and thanks for popping in to check out our weekly round-up of all the stuff that you might have missed across the Steel Media network. Yeah, that's right, it's a big ol' network. Obviously 148Apps is the best, but there are some... | Read more »
All the best games on sale for iPhone an...
It might not have been the greatest week for new releases on the App Store, but don't let that get you down, because there are some truly incredible games on sale for iPhone and iPad right now. Seriously, you could buy anything on this list and I... | Read more »
Everything You Need to Know About The Fo...
In just over a week, Epic Games has made a flurry of announcements. First, they revealed that Fortnite—their ultra-popular PUBG competitor—is coming to mobile. This was followed by brief sign-up period for interested beta testers before sending out... | Read more »
The best games that came out for iPhone...
It's not been the best week for games on the App Store. There are a few decent ones here and there, but nothing that's really going to make you throw down what you're doing and run to the nearest WiFi hotspot in order to download it. That's not to... | Read more »
Death Coming (Games)
Death Coming Device: iOS Universal Category: Games Price: $1.99, Version: (iTunes) Description: --- Background Story ---You Died. Pure and simple, but death was not the end. You have become an agent of Death: a... | Read more »
Hints, tips, and tricks for Empires and...
Empires and Puzzles is a slick match-stuff RPG that mixes in a bunch of city-building aspects to keep things fresh. And it's currently the Game of the Day over on the App Store. So, if you're picking it up for the first time today, we thought it'd... | Read more »
What You Need to Know About Sam Barlow’s...
Sam Barlow’s follow up to Her Story is #WarGames, an interactive video series that reimagines the 1983 film WarGames in a more present day context. It’s not exactly a game, but it’s definitely still interesting. Here are the top things you should... | Read more »
Pixel Plex Guide - How to Build Better T...
Pixel Plex is the latest city builder that has come to the App Store, and it takes a pretty different tact than the ones that came before it. Instead of being in charge of your own city by yourself, you have to work together with other players to... | Read more »
Fortnite Will Be Better Than PUBG on Mob...
Before last week, if you asked me which game I prefer between Fortnite Battle Royale and PlayerUnknown’s Battlegrounds (PUBG), I’d choose the latter just about 100% of the time. Now that we know that both games are primed to hit our mobile screens... | Read more »

Price Scanner via

Back in stock: 13-inch 2.5GHz MacBook Pro (Ce...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros (MD101LL/A) available for $829, or $270 off original MSRP. Apple’s one-year warranty is standard, and shipping is free: – 13″ 2.5GHz MacBook... Read more
Apple restocks Certified Refurbished 2017 13″...
Apple has Certified Refurbished 2017 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.8GHz/8GB/128GB MacBook Air (... Read more
8-Core iMac Pro on sale for $4699, save $300
Amazon has the 8-core iMac Pro on sale for $4699 including free shipping. Their price is $300 off MSRP, and it’s the currently lowest price available for an iMac Pro. For the latest up-to-date prices... Read more
10″ 512GB WiFi iPad Pros on sale for $849, sa...
B&H Photo has Space Gray and Rose Gold 10.5″ 512GB WiFi iPad Pros on sale for $849. Their price is $150 off MSRP, and it’s the lowest price available for these models, new, from any Apple... Read more
MacBook Pro sale! B&H drops prices on new...
B&H Photo has dropped prices on new 2017 13″ MacBook Pros, with models now on sale for up to $200 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only. Their... Read more
13″ MacBook Airs on sale for $100-$150 off MS...
B&H Photo has 13″ MacBook Airs on sale for $100-$150 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 13″ 1.8GHz/128GB MacBook Air (MQD32LL/A): $899, $... Read more
Huge iMac sale! Apple reseller now offering 2...
B&H Photo has new 2017 21″ & 27″ iMacs on sale today for up to $300 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 27″ 3.8GHz iMac (MNED2LL/A): $... Read more
Sale! 1.4GHz Mac mini for $399, $100 off MSRP
B&H Photo has the 1.4GHz Mac mini on sale for $399 for a limited time. Their price is $100 off MSRP, and it’s the lowest price available for a mini from any Apple reseller: – 1.4GHz Mac mini (... Read more
Sale of the year continues as Apple resellers...
Adorama has new 2017 15″ MacBook Pros on sale for $250-$300 off MSRP. Shipping is free, and Adorama charges sales tax in NJ and NY only: – 15″ 2.8GHz Touch Bar MacBook Pro Space Gray (MPTR2LL/A): $... Read more
iPad sale continues! 9″ WiFi iPads for $50-$8...
Walmart has 9.7″ Apple iPads on sale for $50-$80 off MSRP for a limited time. Sale prices are for online orders only, in-store prices may vary: – 9″ 32GB iPad: $249.99 $80 off – 9″ 128GB iPad: $379 $... Read more

Jobs Board

*Apple* Genius - Technical Customer Service...
Job Description: Job Summary As a Genius at the Apple Store, you maintain customers' trust in Apple as the skilled technical customer service expert, Read more
*Apple* Genius - Technical Customer Service...
Job Description:Job SummaryAs a Genius at the Apple Store, you maintain customers' trust in Apple as the skilled technical customer service expert, Read more
*Apple* Retail Sales Associate / Service Wri...
Job Description iStore is the premier retailer of Apple products and solutions. We're looking for dedicated individuals with a passion to simplify and enhance the Read more
*Apple* Senior Manager - Multi Unit Manageme...
…and opportunities of a continuously evolving business is what makes leadership at the Apple Store a rewarding career. It's your job as a Senior Manager to lead Read more
*Apple* Technician - Visual Dynamics, Inc. (...
Job Description Visual Dynamics, Inc., Brevard's Apple Premier Partner, is looking for a dynamic individual to fill the Apple Technician position at our Viera Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.