TweetFollow Us on Twitter

Jan 94 Tips
Volume Number:10
Issue Number:1
Column Tag:Tips & Tidbits

Tips & Tidbits

By Neil Ticktin, Editor-in-Chief

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Tip Of The Month

The 6-byte Code Resource Stub Trick

Many Macintosh programmers who have debugged a CDEF, LDEF, MDEF, or WDEF know “the 6-byte code resource stub trick.” Its been covered in MacTech Magazine, and the wisdom is often passed along online.

To briefly summarize, instead of burying all the code inside a separate code resource where it can't see the structure of the main program (global variables and functions), the programmer creates a 6-byte code stub. In that stub is one MC68000 jump-absolute instruction (as hex in a resource: 4EF9 0000 0000). The programmer replaces the jump destination address (the trailing 32 bits of 0) at runtime with a function address, then informs the relevant Toolbox manager that it should use the resource to define a control, list, or window. (Using this trick with a menu is similar.) Since code is modified, it's always safest to flush the CPU's instruction cache to avoid confusing (read: crashing) it. Refer to the Apple DSC Technical Note "Cache As Cache Can" for the long story.

Now, instead of reading and understanding the tech note and including relevant compensations in your code, you can use a different code resource stub. This stub still includes the function address, but it uses MC68000 instructions to retrieve the address as data, avoiding the code modification problem. In hex: 2F3A 0004 4E75 0000 0000. The 32 bits of zero are again the address you replace with a function address. A disassembly might read:

/* 1 */
MOVE.L  *+$0006,-(A7); push the DC.L onto the stack for RTS
RTS; jump to the definition function
DC.L  0 ; placeholder for addr of defn function

Since the DC.L never actually runs as code, there's no risk of confusing the cache in the CPU. You can use the following C structure declaration to access the address:

/* 2 */
typedef struct
 short  push [2], rts;
 void *addr;
tCodeStub, *tCodeStubP, **tCodeStubH;

- Pete Gontier

Berkeley, CA

This column is your opportunity to spread the word about little bits of information that you find out about. These tidbits can be programming related or they can be user tips that are particularly useful to programmers.

MacTech Magazine will pay $25 for every tip used, and $50 for the Tip of the Month. Or you can take your award in orders or subscriptions.

To submit a tip, send in a letter to the magazine. E-mail is our preferred method, but feel free to send something via the US Mail. See page two for all addresses. If you do send snail mail, enclose a printed copy and a disk copy of the letter so that it does not have to be retyped.

Precomputing Static value in constants

The compiler is not always smart enough to precompute static values in your code. Static values are values that stay constant throughout the program and cannot be changed. By use of constants you can help to compile precomputed values. This saves time and space in your program.

For example, the compiler will generate code to compute the value of the next expression at runtime. The code will be larger and slower.

  someValue := 5 * 4 + anotherValue + 90;

But, if you use a constant to compute the static value in the above expression, the compiler will precompute the value and place it in your compiled object code. The code will be smaller and faster as a result. Change the above expression like this:

  kPrecomputedStaticValue = 5 * 4 + 90;

someValue := kPrecomputedStaticValue + 
(* Other code *)

- Marek Hajek

Incline Village, Nevada

Toggle Invisibles Part 2

I read Lee Rimar’s tip "Toggle Invisibles in MPW" in November, 1993 Tips & Tidbits column. I found Mr. Rimar's script useful, and I've modified it to avoid making assumptions about the auto-indent and lock-scroll options. The trick is to use "=~" to match a regular expression against the three-character result of Format, and extract the second character into the ®1 variable (see "help patterns" in MPW). (If you're running out of sensible Command-key combinations, you can use SetKey instead, in MPW 3.3, to set up a function key, keypad key, control key, or whatever.)

AddMenu Edit "Toggle Invisibles/¥" 
  '(evaluate "`Format "{active}" -x a`" =~ /?(?)®1?/ ) > Dev:Null ; 
  if {®1}=="i" ; 
    Format "{Active}" -a I ; 
  else ; 
    Format "{Active}" -a i ; 

- Dave Lyons

Apple Computer, Inc.

International system Tip

Attention all single-byte developers!! Your software is ugly on double-byte machines! (see screen shot) Why? Because any resource that contains an odd number of text characters has an extra character added to the end (the second byte). Here in Japan, quality is very important and having funky looking characters on every menu and dialog box certainly doesn't convey quality. So what to do?

1. Startup your Mac with a double-byte system disk (check any CD-ROMS you have from Apple for a Japanese "Disk Tools" image.) Don't worry if you can't read Japanese because the menu items and short-cut keys are the same.

2. Launch ResEdit and open your application's resources (also notice ResEdit has the extra characters too! A little sloppy for Apple.)

3. Simply open each of you application's resources and find the foreign characters and backspace over them. Be sure to check everything!! Buttons, dialogs, text strings, etc. If it has text, it is possible there is problems.

4. When your finished, launch your application (while still in Japanese mode) and verify that it looks and runs correctly.

5. Restart your system and you're back to where you were! (Warning: depending upon the version you use, your desktop may be rebuilt on restart)

Even if you don't officially sell your software in Japan, most titles are available as gray market imports (even though the package says in big letters "For Sale in The USA Only".) So take a few minutes to improve your reputation for quality!

- Brett Bibby

Tokyo, Japan


Community Search:
MacTech Search:

Software Updates via MacUpdate

The best games like Animal Crossing on m...
Animal Crossing amiibo Festival is out right now for the Wii U, reminding us of just how much fun that world can be. Or at least to go back and check in on our villages once in a while. [Read more] | Read more »
Between 2 Taps - Tap for Tap interview M...
Hello, and welcome back to Between 2 Taps, Tap for Tap’s Indie Dev interview series. [Read more] | Read more »
Facility 47 (Games)
Facility 47 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: You wake up alone and freezing in an icy cell. You try the cell door but it’s locked, it seems that you are stuck with no... | Read more »
The best Photoshop alternative on iPad
Instagram and Lightroom are great and all, but sometimes people need to get extra creative with their image editing.Like, Photoshop creative. If you're one of these people, take a look at our pick for the best mobile Photoshop experience on iPad... | Read more »
The Walking Dead: No Man’s Land guide -...
A new update for The Walking Dead: No Man’s Land was released last week, making it the perfect time for you to head back to your base and take out some walkers. Here’s the lowdown on what’s new to the game, and how to take advantage. [Read more] | Read more »
Goat Rider guide - Tips and tricks to st...
We've all been there. One second, we're riding high on a crazed goat, and the next, we've been tossed off it like someone who's no good at goat ridin'. [Read more] | Read more »
Real Boxing 2 CREED: How to become a gre...
Just in time for Rocky fans who can’t wait to see CREED, the latest movie, we have the official tie-in game,Real Boxing 2 CREED. It builds on the success of its predecessor and there’s lots to take in so we at 148apps thought we’d run you through... | Read more »
CoinOp Heroes 2 guide - How to build an...
CoinOp Heroes 2 justlaunched and, like all clickers, it's dangerously addictive stuff. You have to furiously tap your screen to defeat wave after wave of foes and earn an insane amount of cash to spend on character upgrades and an army of minions... | Read more »
Dr. Panda Firefighters (Education)
Dr. Panda Firefighters 1.0.1 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0.1 (iTunes) Description: FIGHT FIRES AND SAVE THE DAY!Work together with Dr. Panda and his firefighting team to rescue his trapped... | Read more »
Puddle + (Games)
Puddle + 1.0 Device: iOS iPhone Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Puddle is back in a new "+" edition featuring enhanced graphics, new videos and Apple TV support ! No IAP and No Ads. Dive into Puddle... | Read more »

Price Scanner via

Save $30-$40 on new Apple TVs after rebate
Adorama has new Apple TVs on sale for up to $40 off MSRP after mail-in rebate, good through December 15th. Shipping is free, and Adorama charges NY & NJ sales tax only: - 32GB Apple TV: $119.99... Read more
13-Inch Haswell MacBook Air At Two Years – Th...
The 13-inch mid-2013 “Haswell” MacBook Air I ordered in Apple’s November 2013 Black Friday sale was my first new Mac in four and a half years — the longest interval I’ve gone between system upgrades... Read more
Target Black Friday Early Access deals: $100...
Target is offering early access to their Black Friday deals on Apple products on their online store for today, the 25th, only. Choose free shipping or free local store pickup (if available): - Apple... Read more
BlackBerry Q3 Mobility Index Report Finds iOS...
BlackBerry has announced results of its thirteenth Good Mobility Index Report, showing that organizations are increasingly building custom secure apps. Among Good Powered by BlackBerry (formerly Good... Read more
Wednesday roundup of early Black Friday Mac s...
Save up to $500 on a new Mac with these early Black Friday deals from Apple resellers, currently the lowest prices available for these models: (1) B&H Photo has all new Macs on sale for up to $... Read more
iPod nano on sale for $119, $30 off MSRP
Walmart has the 16GB iPod nano (various colors) on sale for $119.20 on their online store for a limited time. That’s $30 off MSRP. Choose free shipping or free local store pickup (if available). Sale... Read more
Adorama Black Friday deals: Up to $400 off Ma...
Adorama has released their Black Friday deals for 2015. Save up to $400 on MacBook Pros, $200 on MacBooks and MacBook Airs, and $270 on iMacs. Use code RYBFDEAL during checkout to see these prices.... Read more
B&H Photo Deals: $200 off 12-inch 1.2GHz...
In addition to the B&H Photo Black Friday week sales we posted yesterday, B&H has lowered their price on two products to $200 off MSRP: - 12″ 1.2GHz Gray Retina MacBook: $1399 save $200 - 13... Read more
Best Buy Early Access: Today only, Up to $125...
Best Buy has iPad Air 2s on sale for up to $125 off MSRP and Apple Watch models on sale on their online store for up to $100 off MSRP with special codes through midnight CT tonight. Choose free... Read more
UPPERCASE DESIGNS Premium Ultra Thin Keyboard...
UPPERCASE Designs today announced its new Premium Ultra Thin Keyboard Protector and its Palm Rest Protector Set for the 12-inch MacBook. The accessories provide durable protection for the 12-inch... Read more

Jobs Board

Hardware Systems Integration Engineer - *App...
# Hardware Systems Integration Engineer - Apple Watch Job Number: 39380139 Santa Clara Valley, Califo ia, United States Posted: Apr. 23, 2015 Weekly Hours: **Job Read more
Sr. Technical/Project Manager, *Apple* Educ...
# Sr. Technical/Project Manager, Apple Education Job Number: 36588557 New York City, New York, United States Posted: Jul. 30, 2015 Weekly Hours: 40.00 **Job Summary** Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Merchant Operations Manager: *Apple* Pay -...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more than Read more
*Apple* Pay QA Manager - Apple Inc. (United...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more than Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.