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

NetShade 6.3.1 - Browse privately using...
NetShade is an anonymous proxy and VPN app+service for Mac. Unblock your Internet through NetShade's high-speed proxy and VPN servers spanning seven countries. NetShade masks your IP address as you... Read more
Dragon Dictate 4.0.7 - Premium voice-rec...
With Dragon Dictate speech recognition software, you can use your voice to create and edit text or interact with your favorite Mac applications. Far more than just speech-to-text, Dragon Dictate lets... Read more
Persecond 1.0.2 - Timelapse video made e...
Persecond is the easy, fun way to create a beautiful timelapse video. Import an image sequence from any camera, trim the length of your video, adjust the speed and playback direction, and you’re done... Read more
GIMP 2.8.14p2 - Powerful, free image edi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more
Sandvox 2.10.2 - Easily build eye-catchi...
Sandvox is for Mac users who want to create a professional looking website quickly and easily. With Sandvox, you don't need to be a Web genius to build a stylish, feature-rich, standards-compliant... Read more
LibreOffice - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
f.lux 36.1 - Adjusts the color of your d...
f.lux makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day. Ever notice how people texting at night have that eerie blue glow? Or wake... Read more
VirtualBox 5.0.2 - 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
File Juicer 4.43 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. In computer... Read more
Apple MainStage 3.2 - Live performance t...
MainStage 3 makes it easy to bring to the stage all the same instruments and effects that you love in your recording. Everything from the Sound Library and Smart Controls you're familiar with from... Read more

ReBoard: Revolutionary Keyboard (Utilit...
ReBoard: Revolutionary Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: Do everything within the keyboard without switching apps! If you are in WhatsApp, how do you schedule a... | Read more »
Tiny Empire (Games)
Tiny Empire 1.1.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1.3 (iTunes) Description: Launch cannonballs and blow tiny orcs into thousands of pieces in this intuitive fantasy-themed puzzle shooter! Embark on an... | Read more »
Astropad Mini (Productivity)
Astropad Mini 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: *** 50% off introductory price! ​*** Get the high-end experience of a Wacom tablet at a fraction of the price with Astropad... | Read more »
Emo Chorus (Music)
Emo Chorus 1.0.0 Device: iOS Universal Category: Music Price: $1.99, Version: 1.0.0 (iTunes) Description: Realistic Choir simulator ranging from simple Chorus emulation to full ensemble Choir with 128 members. ### introductory offer... | Read more »
Forest Spirit (Games)
Forest Spirit 1.0.5 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.5 (iTunes) Description: | Read more »
Ski Safari 2 (Games)
Ski Safari 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: The world's most fantastical, fun, family-friendly skiing game is back and better than ever! Play as Sven's sister Evana, share... | Read more »
Lara Croft GO (Games)
Lara Croft GO 1.0.47768 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.47768 (iTunes) Description: Lara Croft GO is a turn based puzzle-adventure set in a long-forgotten world. Explore the ruins of an ancient... | Read more »
Whispering Willows (Games)
Whispering Willows 1.23 Device: iOS Universal Category: Games Price: $4.99, Version: 1.23 (iTunes) Description: **LAUNCH SALE 50% OFF** - Whispering Willows is on sale for 50% off ($4.99) until September 9th. | Read more »
Calvino Noir (Games)
Calvino Noir 1.1 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: The film noir stealth game. Calvino Noir is the exploratory, sneaking adventure through the 1930s European criminal underworld.... | Read more »
Angel Sword (Games)
Angel Sword 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: Prepare to adventure in the most epic full scale multiplayer 3D RPG for mobile! Experience amazing detailed graphics in full HD.... | Read more »

Price Scanner via

Big Grips Lift Handle For iPad Air and iPad A...
KEM Ventures, Inc. which pioneered the extra-large, super-protective iPad case market with the introduction of Big Grips Frame and Stand in 2011, is launching Big Grips Lift featuring a new super-... Read more
Samsung Launches Galaxy Tab S2, Its Most Powe...
Samsung Electronics America, Inc. has announced the U.S. release of the Galaxy Tab S2, its thinnest, lightest, ultra-fast tablet. Blending form and function, elegant design and multitasking power,... Read more
Tablet Screen Sizes Expanding as iPad Pro App...
Larger screen sizes are gaining favor as the tablet transforms into a productivity device, with shipments growing 185 percent year-over-year in 2015. According to a new Strategy Analytics’ Tablet... Read more
Today Only: Save US$50 on Adobe Elements 13;...
Keep the memories. lose the distractions. Summer’s winding down and it’s time to turn almost perfect shots into picture perfect memories with Elements 13. And get the power to edit both photos and... Read more
1.4GHz Mac mini on sale for $449, save $50
Best Buy has the 1.4GHz Mac mini on sale for $50 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Price for online orders only, in-store price may vary... Read more
12-inch 1.1GHz Gold MacBook on sale for $1149...
B&H Photo has the 12″ 1.1GHz Gold Retina MacBook on sale for $1149.99 including free shipping plus NY sales tax only. Their price is $150 off MSRP, and it’s the lowest price available for this... Read more
27-inch 3.3GHz 5K iMac on sale for $1849, sav...
Best Buy has the 27″ 3.3GHz 5K iMac on sale for $1849.99. Their price is $150 off MSRP, and it’s the lowest price available for this model. Choose free shipping or free local store pickup (if... Read more
Worldwide Tablet Shipments Expected to Declin...
Does Apple badly need a touchscreen convertible/hybrid laptop MacBook? Yes, judging from a new market forecast from the International Data Corporation (IDC) Worldwide Quarterly Tablet Tracker, which... Read more
Continued PC Shipment Shrinkage Expected Thro...
Worldwide PC shipments are expected to fall by -8.7 percent in 2015 and not stabilize until 2017, according to the latest International Data Corporation (IDC) Worldwide Quarterly PC Tracker data. The... Read more
Imminent iPhone 6s Announcement Leads To 103%...
NextWorth Solutions, with its online and in-store electronics trade-in programs including, reports that it has experienced a 103 percent surge in quoted trade-in values over the... Read more

Jobs Board

*Apple* Retail Online Store: Customer Insigh...
**Job Summary** Apple Retail (Online Store) is seeking an experienced e-commerce analytics professional to join the Customer Insights Team. The Web e-Commerce Analyst Read more
*Apple* Music, Business Operations - Apple I...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
WW *Apple* Retail Online Store: Customer In...
**Job Summary** The Apple Retail - Online Store is seeking an experienced web merchandising analytics professional to join the Customer Insights Team. The Web Read more
Senior Payments Security Manager - *Apple*...
**Job Summary** Apple , Inc. is looking for a highly motivated, innovative and hands-on senior payments security manager to join the Apple Pay security team. You will Read more
Software QA Engineer, *Apple* Pay Security...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.