TweetFollow Us on Twitter

Apr 89 Letters
Volume Number:5
Issue Number:4
Column Tag:Letters


By David E. Smith, Editor & Publisher, MacTutor

Aztec C

Rich Heady

San Diego, CA

Aztec C is all I was told it would be, and I’m already pleased with the results. It is particularly gratifying to have access to “intermediate code” again after being locked inside Lightspeed C’s projects for the past 18 months, and more gratifying still to find the assembly code already optimized to the point where I may not need to go through cleaning up the little stupidities. There is nothing wrong with Lightspeed C; in fact, it remains a superior prototyping environment. But at the point where I began to look beyond the prototype to a shippable product, it was a relief to find Aztec C ready to finish the job. Aztec C might carve a bigger niche in the Macintosh world by appealing to the “1 Meg programmer” who wants to produce polished code without larding on RAM and without wading into the complexity of MPW.

Typos upon Typos

Ajay Nath

Oakland Gardens, NY

I’ve been writing a driver for my plotter, and I’ve been looking at the code you presented in MacTutor, Volume 3, Number 11 and 12. I’ve caught some errors in the code you presented on page 57 (#12). The code in the procedure DrvrStorage():


asm {
 MOVEQ  #8, D0
 MOVE.L UTableBase, A0
 MOVE.L (A0), OutDctlEntry

I wrote to you about this error before, but you printed my correction incorrectly! (You did print my explanation of why the author’s code was wrong correctly.) [Sorry, we will double our efforts. -ed]

On page 59 in the procedure MyPrDlgMain() at the end of this proc a pointer is freed and then accessed as follows:

/* 2 */

free(+p); /*ptr is being freed by a subroutine */
if (tp->fDolt) (void) MyPrValidate(hPrint);
 /*we accessed the ptr we freed */
return (tp->fDolt); /* you did it again! */

if (tp->fDolt) is true the subroutine “MyPrValidate” will be called, and it calls traps like GetResource and LoadResource which will move memory so that doing a subsequent “return(tp->fDolt)” may be pointing to garbage.

One way to fix this is to do the following:

/* 3 */

{ Boolean theResult; 
 /* a local variable to hold function result */
theResult = tp->fDolt; /*save the value of fDolt */
free (tp);
if (theResult) (void) MyPrValidate(hPrint);
return (theResult);

on page 58 in the procedure “MyPrintDefault(hPrint)” one of the lines:

**hPrint = **theDefault;

the same line appears on page 59 near the end of the procedure MyPrValidate(hPrint)

What the author is trying to do is to fill in the fields of the data structure that hPrint points to, what he actually does is mess up the hPrint handle. What he should do is something like this:

/* 4 */
BlockMove(*theDefault, *hPrint, sizeof(TPrint));

and probably:

/* 5 */

 /* unload resource now that we’re done */

It is a good article which provides information on how to write printer drivers, but some of the code is incorrect.

In MacTutor, Vol. 4, #11, the code presented by Donald Koscheka to do a string comparison uses the “DBRA” instruction incorrectly. When you loop using “DBRA” you use the word (16 bits) in the register you use as a loop counter; Mr. Koscheka uses register D1 as his loop counter and sets its value by doing:

 MOVE.B (A))+, D1; get length of string 1

This sets the lower 8 bits of D1, NOT the lower word. The correct way to load the value of the loop counter in this case is to:


            MoveQ #0, D0; set D0 = 0;
            Move.B(A0)+, D0      ; D0 = string length

Also when using the “DBRA” instruction, the register must actually have the loop count -1 in it, i.e. if you want to loop 10 times, put 9 in the register. Mr. Koscheka doesn’t do this. I realize that he was showing a code fragment, but the purpose of his article was to show how to use assembly language and allowing such errors to slip in does readers a disservice.

FORTRAN Math Libraries

Michael M. J. Tracy

Pittstown, NJ

I am writing in response to Tatsuhito Koya’s request (Feb 1989, Vol. 5 No. 2) for information on FORTRAN math libraries that will run on the Mac. There is an excellent book out called ‘Numerical Recipes: The Art of Scientific Computing’ by William H. Press, Brian P. Flannery, Saul A. Teukolsky & William T. Vetterling (Cambridge University Press, ISBN 0 521 30811 9). I refer to this book infinitely more often than ‘Inside Macintosh’ when writing scientific applications on the Mac (and it’s cheaper too, about $35 hard cover). The book provides the source code for over 200 subroutines. Its real value to the user, however, is in the eloquent and intelligent discussion of the principles underlying each algorithm, explaining the strengths and weaknesses, and usually providing alternative algorithms so that the cautious user can cross check results. I have learned a lot from this book. Listing from the contents page, the book covers; solution of linear algebraic equations; interpolation and extrapolation; integration of functions; evaluation of functions; special functions; random numbers; sorting; root finding and non-linear sets of equations; minimization and maximization of functions; eigensystems; fourier transform spectral methods; statistical description of data; modeling of data; integration of ordinary differential equations; two point boundary value problems; partial differential equations. There are two versions of the book. The original edition gave the subroutine listings in both FORTRAN and Pascal. By popular demand, a second version was released which presents the C source code listings (written somewhat from the perspective of a FORTRAN programmer who wishes to convert to C, and provides structures and functions for handling complex numbers). Macintosh compatible disks containing the source code are also available from the publishers.

All FORTRAN subroutines that I have used work well, and have compiled without any problems under both MacFortran and Language Systems Fortran. Some subroutines, however, need to have the ‘SAVE’ statement added at the beginning (as required by the ANSI 77 FORTRAN standard) if local variables need to be preserved between subroutine calls, such as in the random number generators.

Further Optimizations

John F. Reiser

Beaverton, OR

The code for optimized string comparisons (Letters, Jan. ’89, p. 106) is on the right track, but the listing contains a bug and the inner loop can be improved further. If the length of the first string is 128 or more, then the iteration count in register D1 gets an incorrect value via sign extension using EXT.W. The loop can be shortened by combining the break-out test with the iteration count control:


A0 -> Pascal string 1
A1 -> Pascal string 2
D0 <- 0 if not equal, 1 if equal

CompareString  Moveq #0,D0; clear high bits
 Move.B (A0), D0 ; length of first string
@10Cmp.B(A0)+, (A1)+ ; mismatch?
 Dbne D0, @10  ; stop when .ne., or at end
 Sne  D0; D0.B = -1 if .ne.; 0 if .eq.
 Addq.B #1, D0 ; D0.B = 0 if .ne.; 1 if .eq.
 Ext.W  D0; Dbne can set bits 7-15

VBL Animation Problems

David Oster

Berkeley, CA

I am appalled by Dick Chandler’s article, “VBL Task Animation” in the February 1989 issue of MacTutor. Yes, his program works, but only because it is a top. Any real program that tries the technique he describes will fail miserably.

Look, his VBL task calls GetIcon and PlotIcon at VBL interrupt time. In his application, the main loop just busy waits for the user to press the Button. A real application would be calling GetNextEvent(), or doing something. For example, each time the user looks at a menu. When the menu goes away, it slams those bits back and deallocates the handle.

GetIcon calls GetResource(). What if the VBL task calls it while the Memory Manager is shuffling the heap to allocate memory for the main loop. Crash city. PlotIcon calls CopyBits(), which clips against the clipRgn and visRgn of the underlying grafPort. What if the VBL task calls it while the Memory Manager is shuffling the heap to allocate memory for the main loop? Crash city.

Even if your program is clean, you do not know what trap patches the user has installed: Maybe he is using an INIT that overrides some trap your program needs, and the override will do memory allocation. For example, Dick’s program calls Button() from its main loop, and many INITs override button, so they will get called while the mouse is down.

So, you can only do animation at interrupt time if you can guarantee that no user or system task will allocate memory in the main loop.

Dick’s program doesn’t guarantee this, since it calls Button() from its main loop, and Button() may have been overriden by an INIT. Since there is so little the main loop can safely do, you might as well give up on VBL Task animation, and just do animation in your main loop, busy waiting until TickCount changes to pause between animation frames.

TWindow Manager Update

Thomas Fruin

Las Condes, Santiago, Chile

After a four month trek through the Latin American country of Peru (that left me penniless), I was delighted upon arrival at my fathers place in Santiago de Chile to find last December’s copy of MacTutor with my Tool Window Manager article. And the generous cheque that was included couldn’t have come at a better time!

Since the article was sent off to you, several programs have been written making use of TWindow. This caused a few small bugs to surface. I would like to take this opportunity to correct them.

The TWindow Manager incorrectly assumes that the calling application will always process every activate or deactivate event by calling TGetNextEvent. However, when multiple dialog boxes are put up, or dialogs following other dialogs without a call to TGetNextEvent in between, some activate or deactivate events may “linger”. This may cause the wrong (de)activation to occur when TGetNextEvent finally is called.

My solution is a utility function FlushActivateEvents(), with the following code:

/* 8 */

static void FlushActivateEvents()

 toBeActivated = toBeDeactivated = nil;
 result = GetNextEvent(activMask, &theEvent);
 result = GetNextEvent(activMask, &theEvent);

When called, this function effectively flushes (removes) every activate and deactivate event from the system: both official events and TWindow Manager internal events.

A call to FlushActivateEvents needs to be inserted in THideWindow and another call in TShowWindow. Both these calls should be made right after the very first if statement, where is checked if the window is still visible or invisible. That is all.

A minor oversight is that the WindowExists function is not defined static. It should be because it is internal to the TWindow Manager.

Finally, I can announce that I have written an MPW Pascal INTERFACE unit, that allows you to call the TWindow Manager from MPW pascal programs. This required more small modifications to the TWindow Manager source. As soon as I get someone to send me my disks from Holland, I will send the new versions of the software to MacTutor. By the way, this version of software also includes a TWaitNextEvent (although this is a trivial addition).

Publication of my article has definitely encouraged me to write more, so expect to see other stuff from me!

Absoft MacFortran to LS Fortran

Bert Waggoner

Riverside, CA

After over a year of reading your journal and programming the Macintosh things are beginning to make a little sense. Now I’d like to give a little back. Here are some notes on the new Language Systems Fortran compiler for MPW that you may wish to pass on to other readers:

I just received the Language Systems (LS) Fortran compiler v1.2 for MPW, and it looks very good. Now, using MPW, I can code in C and have access to the vast array of scientific subroutines written in Fortran (including those of my boss, who is reluctant to learn another language. We are developing chemical transport models for the Macintosh, and, until now, I have been translating his Fortran code to Think C. Microsoft C and Fortran for the IBM PC’s have been on speaking terms for some time - it’s about time the Mac caught up).

Here are some changes I had to make to get an Absoft MacFortran program to compile with LS Fortran:

- the preconnected file units for screen and printer I/O are reversed!

- any WHILE ( )/REPEAT loops must be replaced by DO WHILE ( )/END DO,

- LS Fortran doesn’t have a SELECT CASE statement (sigh),

- IF statements must have enclosing parentheses, i.e. use IF (X .EQ. Y) THEN, not IF X .EQ. Y Then,

- the ACCEPT statement must specify a format,

- there were several differences in filing handling, such as no POSITION or ACCESS key words for the OPEN statement IN LS Fortran.

There are, undoubtably, many other differences. As for toolbox access, LS Fortran’s implementation is different and cleaner, and the language allows for structures. Last, but not least, LS Fortran has a decent manual with lots of examples. Now my problem is converting my Think C code to MPW C. Would any readers like to share their experiences with this?

SysEnvirons From MacFortran

James Wishart

Long Island, NY

In the course of developing an instrument control and data acquisition application in Absoft MacFortran/020, I needed to call SysEnvirons to check for the 68881 floating point processor. Unfortunately, Absoft did not include the trap dispatch parameter for the call in their include files. With the help of additional documentation on the Toolbx.sub routine provided by Lee Rimar of Absoft, I found the correct parameter to be z’09014010'. The following program demonstrates how to call SysEnvirons in Absoft MacFortran.

c 9

program TestSysEnvirons
implicit none

integer*4 toolbx
integer*2 oserr, i
integer*4 version

integer*1 SysEnvRec(16)

integer*2 environsVersion
integer*2 machineType
integer*1 systemVersion(2)
integer*2 processor
logical*1 hasFPU
logical*1 hasColorQD
integer*2 keyBoardType
integer*2 atDrvrVersNum
integer*2 sysVRefNum

equivalence (SysEnvRec(1), environsVersion)
equivalence (SysEnvRec(3), machineType)
equivalence (SysEnvRec(5), systemVersion(1))
equivalence (SysEnvRec(7), processor)
equivalence (SysEnvRec(9), hasFPU)
equivalence (SysEnvRec(10), hasColorQD)
equivalence (SysEnvRec(11), keyBoardType)
equivalence (SysEnvRec(13), atDrvrVersNum)
equivalence (SysEnvRec(15), sysVRefNum)

Parameter (SYSENVIRONS = Z’09014010')
oserr = 0
version = 2
do (i=1,16)
 SysEnvRec(i) = 0

oserr=toolbx(SYENVIRONS, version, SysEnvRec)

if (oserr .ne. -5501) then
 write(9,*) ‘environsVersion = ‘, environsVersion
 write(9,*) ‘machineType = ‘, machineType
 write(9,1) systemVersion(1), systemVersion(2)
1format(‘systemVersion = ‘, z2, “.”, z2)
 write(9,*) ‘processor = ‘, processor
 write(9,*) ‘hasFPU = “, hasFPU
 write(9,*) ‘hasColorQD = ‘, hasColorQD
 write(9,*) ‘keyBoardType = ‘, keyBoardType
 write(9,*) ‘atDrvrVersNum = ‘, atDrvrVersNum
 write(9,*) ‘sysVRefNum = ‘,sysVRefNum
select case (oserr)
 case (0)
 case (-5500)
 write(9,*) ‘System version is less than 4.2’
 case (-5501)
 write(9,*) ‘Bad version selector - no data returned’
 case (-5502)
 write(9,*) ‘Version ‘, version,’ requested, version ‘,
+environsVersion, ‘ returned.’
 case default
 write(9,*) ‘Unspecified error #’, oserr
end select

write(9,*) ‘Hit RETURN to exit program’

A Usenet message from David Phillip Oster brought my attention to the fact that programs should watch for disk insertion events in their main loops and call DIBadMount if the inserted disk cannot be mounted. Implementing this feature requires two more undocumented trap dispatch parameter, DIBadMount (z’9E952200', routine #0) and DIUnload (z’9E908000', routine #4) from Pack2, Disk Initialization. The following code fragment uses the event manager variables defined in the example in the MacFortran manual. (Notice that the Pack2 routine selector must be added to the end of the argument list.) See Inside Macintosh Vol. 2 for the result codes returned in the two byte variable err.

c 10

select case (what)
 case(7)! 7 = Disk insertion
 if (shift(message, -16) .ne. 0) then
 call toolbx(INITCURSOR)
 err = toolbx(DIBADMOUNT, z’00640064', message, 0)
 call toolbx(DIUNLOAD, 4)

The remaining Pack2 parameters should be as follows, but I have not tested these: DILoad: z’9E908000', routine #2; DIFormat: z’9E949000', routine #6; DIVerify: z’9E949000', routine #8; DIZero: z’9E94E200' or z’9E94C200', routine #10.

I want to thank Jay Lieske for his “Fortran Printing Interface” article in August, 1988 issue as well as all of the people who contributed information about Classic Mac analog board failures. Every month I pace in front of my mailbox until MacTutor arrives.

Author Incentive Program Correction

Kirk Chase

Anaheim, CA

In the December ’89 MacTutor, we made a correction on the Author Incentive Program initiated by Apple. Additional reimbursement is ONLY FOR APPLE EMPLOYEES. Those not employed by Apple DO NOT QUALIFY. We are sorry for any confusion that may have resulted over this and hope this clears up any mistaken notions. If you are with Apple, and if you want more information, please contact Stacey Farmer in public relations, who is now in charge of the program, for more information.


Community Search:
MacTech Search:

Software Updates via MacUpdate

BlueStacks 4.140.13 - Run Android applic...
BlueStacks App Player lets you run your Android apps fast and fullscreen on your Mac. Feature comparison chart Version 4.140.13: Highlights/Bug Fixes: Feel free to use BlueStacks as your go to... Read more
Adobe Premiere Pro CC 2020 14.0.1 - Digi...
Premiere Pro CC 2020 is available as part of Adobe Creative Cloud for as little as $52.99/month. The price on display is a price for annual by-monthly plan for Adobe Premiere Pro only Adobe Premiere... Read more
VirtualBox 6.1.2 - x86 virtualization so...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
RoboForm 8.6.8 - Password manager; syncs...
RoboForm is a password manager that offers one-click login, mobile syncing, easy form filling, and reliable security. Password Manager. RoboForm remembers your passwords so you don't have to! Just... Read more
Postbox 7.0.11 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
calibre 4.9.0 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Notability 4.2 - Note-taking and annotat...
Notability is a powerful note-taker to annotate documents, sketch ideas, record lectures, take notes and more. It combines, typing, handwriting, audio recording, and photos so you can create notes... Read more
FoldersSynchronizer 5.0.1 - Synchronize...
FoldersSynchronizer is a popular and useful utility that synchronizes and backs-up files, folders, disks and boot disks. On each session you can apply special options like Timers, Multiple Folders,... Read more
Sketch 62 - Design app for UX/UI for iOS...
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
ScreenFlow 9.0.2 - Create screen recordi...
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

Latest Forum Discussions

See All

Slingsters is a physics-based puzzler fo...
Slingsters is a physics-based puzzle game where the aim is to collect various different monsters by flinging them from one side of a level to the other and into a box. It's also the first game from Nappy Cat and is available now for iOS and... | Read more »
Spiritwish's latest update sees the...
A sizeable update has hit Nexon's MMORPG Spiritwish today. It brings a new game mode, characters and there will also be a special event to celebrate the update with a firework display. [Read more] | Read more »
Maze Machina, a turn-based puzzler from...
The latest game from Arnold Rauers also known as Tiny Touch Tales is now available. You may be familiar with one of his many excellent titles such as Card Crawl, Enyo and Card Thief. His latest endeavour is called Maze Machina and you can grab it... | Read more »
Mario Kart Tour's Ice Tour races to...
Can you believe Mario Kart Tour is already on its 9th tour? The game only launched back in September, and since then it's become increasingly tricky to keep on top of the amount of new content Nintendo is pumping out. [Read more] | Read more »
Apple Arcade: Ranked - Top 50 [Updated 1...
In case you missed it, I am on a quest to rank every Apple Arcade game there is. [Read more] | Read more »
Marvel Future Fight's latest update...
Marvel Future Fight's latest update has added an all-new team of heroes to recruit and do battle with. The 'Warriors of the Sky' include Blue Dragon, War Tiger, Sun Bird, and Shadow Shell. As is the norm, each character comes with their own unique... | Read more »
Klee: Spacetime Cleaners is a fast-paced...
Klee: Spacetime Cleaners is a fast-paced auto-shooter that sports a cute retro aesthetic thathad racked up an impressive 100,000 pre-registers prior to its release. It's available now for both iOS and Android. [Read more] | Read more »
Hearthstone's latest solo adventure...
Blizzard has unveiled a plethora of details about its upcoming expansion for its popular card game Hearthstone. It's called Galakrond's Awakening and will bring the Year of the Dragon storyline to a close. It's available now for pre-purchase ahead... | Read more »
Cultist Simulator's Dancer DLC laun...
Cultist Simulator's Dancer DLC is set to launch for iOS and Android on January 22nd. It revolves around the occult cabaret known as the 'Ecdysis Club', where "the distinction between pleasure and pain is as delicate and essential as the human skin... | Read more »
Death Comes True releases a new characte...
Death Comes True is an FMV murder mystery from Kazutaka Kodaka, the creator of Danganronpa. It sees you playing as an amnesiac young man, called Makoto Karaki, who wakes up in a mysterious hotel to find that he's being hunted for a series of... | Read more »

Price Scanner via

New Verizon deal: Apple iPhone XR for $300 of...
Switch to Verizon and sign up with one of their Unlimited plans, and Verizon will take $300 off the price of an Apple iPhone XR (regularly $749), plus get a free $200 prepaid Mastercard. This is an... Read more
Amazon’s popular AirPods sale is back with mo...
Amazon has new 2019 Apple AirPods on sale today ranging up to $40 off MSRP, starting at $129, as part of their popular Apple AirPods sale. Shipping is free: – AirPods Pro: $234.98 $15 off MSRP –... Read more
Apple’s top of the line 10.5″ 256GB WiFi + Ce...
B&H Photo has the top of the line 10.5″ 256GB WiFi + Cellular iPad Air on sale for $599 shipped. That’s $180 off Apple’s MSRP for this model and the cheapest price available. Overnight shipping... Read more
Apple’s refurbished iPad Pros are the cheapes...
Apple has Certified Refurbished 11″ iPad Pros available on their online store for up to $220 off the cost of new models. Prices start at $679. Each iPad comes with a standard Apple one-year warranty... Read more
Just in: Take $100 off the price of the 3.0GH...
Apple resellers are offering new 2018 6-Core Mac minis for $100 off Apple’s MSRP today, only $999. B&H Photo has 6-Core Mac minis on sale for $100 off Apple’s standard MSRP. Overnight shipping is... Read more
Apple has 4-core and 6-core 2018 Mac minis av...
Apple has Certified Refurbished 2018 Mac minis available on their online store for $120-$170 off the cost of new models. Each mini comes with a new outer case plus a standard Apple one-year warranty... Read more
Amazon offers $200 discount on 13″ MacBook Ai...
Amazon has new 2019 13″ MacBook Airs with 256GB SSDs on sale for $200 off Apple’s MSRP, now only $1099, each including free shipping. Be sure to select Amazon as the seller during checkout, rather... Read more
Apple’s AirPods drop to $129 again at these r...
Apple resellers are offering $30 discounts on Apple AirPods with Charging Case, with prices at $129. These prices are the cheapest new AirPods prices currently available from any Apple reseller: (1)... Read more
Save up to $250 on an iPhone XS with these Ce...
Apple is now offering Certified Refurbished iPhone XS models for up to $350 off MSRP with prices starting at $699. Each iPhone is unlocked and comes with Apple’s standard one-year warranty and a new... Read more
B&H offers 13″ MacBook Airs for $150 off...
B&H Photo has 13″ 128GB MacBook Airs on sale for $150 off Apple’s MSRP, only $949. Overnight shipping is free to many locations in the US: – 13″ 1.6GHz/128GB MacBook Air Space Gray: $949.99 $150... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**745058BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 001080-Lake Charles-Store **Job Read more
Geek Squad *Apple* Consultation Professiona...
**756640BR** **Job Title:** Geek Squad Apple Consultation Professional **Job Category:** Store Associates **Store NUmber or Department:** 000484-Manchester-Store Read more
*Apple* Phenology Coordinator - Montana Stat...
…Rachel Leisso at ### or Classification Title Working Title Apple Phenology Coordinator Brief Position Overview This position provides support for Read more
Business Development Specialist - *Apple* -...
Responsible for driving sales growth specifically for the Apple product line within CDW's account base. Primarily working with CDW and Apple sales teams and Read more
Geek Squad *Apple* Consultation Professiona...
**757640BR** **Job Title:** Geek Squad Apple Consultation Professional **Job Category:** Store Associates **Store NUmber or Department:** 000802-Las Cruces-Store Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.