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: jjt@naucse.cse.nau.edu

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:

{1}

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

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:

Oops!

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

Smultron 10.0.2 - 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
Capto 1.2.5 - $29.99
Capto (was Voila) is an easy-to-use app that takes capturing, recording, video and image editing to the next level. With an intelligent file manager and quick sharing options, Capto is perfect for... Read more
Cocktail 11.0.1 - General maintenance an...
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
Sketch 47.1 - Design app for UX/UI for i...
Sketch is an innovative and fresh look at vector drawing. Its intentionally minimalist design is based upon a drawing space of unlimited size and layers, free of palettes, panels, menus, windows, and... Read more
Slack 2.8.2 - Collaborative communicatio...
Slack is a collaborative communication app that simplifies real-time messaging, archiving, and search for modern working teams. Version 2.8.2: A small release containing nothing but another Electron... Read more
Path Finder 7.6.1 - Powerful, award-winn...
Path Finder makes you a master of file management. Take full control over your file system. Save your time: compare and synchronize folders, view hidden files, use Dual Pane and full keyboard... Read more
Sketch 47.1 - Design app for UX/UI for i...
Sketch is an innovative and fresh look at vector drawing. Its intentionally minimalist design is based upon a drawing space of unlimited size and layers, free of palettes, panels, menus, windows, and... Read more
Cocktail 11.0.1 - General maintenance an...
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
Path Finder 7.6.1 - Powerful, award-winn...
Path Finder makes you a master of file management. Take full control over your file system. Save your time: compare and synchronize folders, view hidden files, use Dual Pane and full keyboard... Read more
Slack 2.8.2 - Collaborative communicatio...
Slack is a collaborative communication app that simplifies real-time messaging, archiving, and search for modern working teams. Version 2.8.2: A small release containing nothing but another Electron... Read more

Dune! guide - how to toe the line and ge...
Publisher Voodoo is at it again with an all new high score chaser -- Dune! In this fast-paced arcade game, you have to propel yourself along sand dunes, gaining enough momentum to jump above the line to score points, while making sure you have... | Read more »
The best deals on the App Store this wee...
Happy Tuesday, dear readers. Your favorite part of the week as officially arrived. It's time to take a look at the best deals in games. Things are admittedly a bit sparse, but there are a few diamonds in the rough to see you through if you're... | Read more »
Be the last person standing in Legacy of...
Yoozoo Games’ popular action MMO Legacy of Discord is getting a huge new update to celebrate its first anniversary. Perhaps the biggest change is the addition of an exciting survival mode titled Last Guardian. This new survival mode will pit you... | Read more »
Home Street guide - how to make friends...
From the creators of Food Street comes Home Street, a new simulation game that tasks you with building a social network and designing a beautiful home. It's a bit like The Sims, but you won't have to worry about the daily chores involved (feeding,... | Read more »
Color Ballz guide - how to bounce to the...
Color Ballz is an addictive new arcade title from Ketchapp Studios. It takes old school mechanics from games like Brickles and puts a fun twist on it. Your job? To catch balls with a paddle and send them back into a chute to be carried back to... | Read more »
Q&A: A-33 Studio explains why Combat...
When it comes to mobile FPS, it’s often tricky to get the fundamentals right on a platform lacking a physical controller, large display and hefty RAM. With Combat Squad: Project Wednesday, A-33 Studio bravely took on the challenge of making a... | Read more »
Taichi Panda 3: Dragon Hunter guide - ti...
Taichi Panda 3: Dragon Hunter launched this week to players all over the world. It's a beautiful mobile MMORPG that blends elements of Eastern and Western fantasy. It reminds us of a mix between World of Warcraft and Jade Empire. MMO's can have a... | Read more »
The best new games we played this week -...
Phew. It has been a week, but now it's time to relax, put your feet up, and enjoy some brand new mobile games. It was a bit of slow week, but there's still plenty of new titles to add to your collection. Here are four of our favorites. [Read... | Read more »
Yoink - Improved Drag and Drop (Product...
Yoink - Improved Drag and Drop 1.0 Device: iOS Universal Category: Productivity Price: $2.99, Version: 1.0 (iTunes) Description: Yoink for iPad and iPhone lets you easily and quickly store items you drag, copy or share, for later use... | Read more »
Cottage Garden (Games)
Cottage Garden 1.11 Device: iOS Universal Category: Games Price: $4.99, Version: 1.11 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

13″ MacBook Pros on sale for up to $120 off M...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for up to $120 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
15″ MacBook Pros on sale for up to $200 off M...
B&H Photo has 15″ MacBook Pros on sale for up to $200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2249, $150... Read more
Roundup of Apple Certified Refurbished iMacs,...
Apple has a full line of Certified Refurbished 2017 21″ and 27″ iMacs available starting at $1019 and ranging up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free... Read more
Sale! 27″ 3.8GHz 5K iMac for $2098, save $201...
Amazon has the 27″ 3.8GHz 5K iMac (MNED2LL/A) on sale today for $2098 including free shipping. Their price is $201 off MSRP, and it’s the lowest price available for this model (Apple’s $1949... Read more
Sale! 10″ Apple WiFi iPad Pros for up to $100...
B&H Photo has 10.5″ WiFi iPad Pros in stock today and on sale for $50-$100 off MSRP. Each iPad includes free shipping, and B&H charges sales tax in NY & NJ only: – 10.5″ 64GB iPad Pro: $... Read more
Apple iMacs on sale for up to $130 off MSRP w...
B&H Photo has 21-inch and 27-inch iMacs in stock and on sale for up to $130 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2179 $... Read more
2017 3.5GHz 6-Core Mac Pro on sale for $2799,...
B&H Photo has the 2017 3.5GHz 6-Core Mac Pro (MD878LL/A) on sale today for $2799 including free shipping plus NY & NJ sales tax only . Their price is $200 off MSRP. Read more
12″ 1.2GHz Space Gray MacBook on sale for $11...
Amazon has the 2017 12″ 1.2GHz Space Gray Retina MacBook on sale for $100 off MSRP. Shipping is free: 12″ 1.2GHz Space Gray MacBook: $1199.99 $100 off MSRP Read more
Bare Bones Software Releases macOS High Sierr...
Bare Bones Software has announced the release and immediate availability of BBEdit 12.0, a significant upgrade to its professional strength text and code editor. BBEdit 12 introduces a new foundation... Read more
Yale Announces Availability of Apple HomeKit-...
Yale Locks & Hardware has announced that Apple HomeKit support for its Assure Lock family is available this month. The new Yale iM1 Network Module, which provides support for the Apple Home app... Read more

Jobs Board

Fraud Analyst, *Apple* Advertising Platform...
Job Summary Apple Ad Platforms has an opportunity to redefine advertising on mobile devices. Apple reaches hundreds of millions of iPhone, iPod touch, and iPad Read more
*Apple* Information Security - Security Data...
Job Summary This role is responsible for helping to strengthen Apple 's information security posture through the identification and curation of security event data. Read more
Lead *Apple* Solution Consultant - Apple In...
…develop a team of diverse partner employees focusing on excellence to deliver the Apple story. Even when you're not present, you will maintain a consistent influence Read more
watchOS Frameworks Engineering Manager, *App...
Job Summary Join the team that is shaping the future of software development for Apple Watch! Apple is looking for an exceptional software engineering leader to Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.