TweetFollow Us on Twitter

Nov 94 Dialog Box
Volume Number:10
Issue Number:11
Column Tag:Dialog Box

Dialog Box

By Scott T Boyd, Editor

Don’t Scream, Send ‘em The Article!

I’d like to applaud Eric Shapiro’s article entitled “Multiple Monitors vs. Your Application”. As a sometimes one, two, or three monitor user I routinely experience everything he griped about. Purchasing multiple monitors is the most cost effective solution for attaining a large on-screen workspace and developers would do well to support it better. (Having multiple monitors has also worked in the past to really freak out some of my IBM user/programmer friends!)

Even Apple has problems writing friendly windowing code. I can’t tell you how many times I’ve disconnected my second monitor to use somewhere else, restarted, launched AppleTalk Remote Access 1.0, and found one of its crucial windows to appear offscreen. I have to reconnect the second monitor, move the windows to the main monitor, and try again! At least when I encounter this bug in Excel I can “arrange” it back on...

I too was aghast to see that the “new version of one popular developer tool” creates the window and then snaps it into position. The first few times I brought up a window I was sure that two were appearing. How could something that obvious slip through, especially when the fix should be a single line of code? Anyway, thanks for the article. If I see one more window jump back to my main monitor when I try to enlarge it on my second monitor by clicking the zoom box, I’ll scream!

- Jeff Mallett, j.mallett@genie.geis.com

PPC Assembly Article Comments

When Bill Karsh repeated last month the worn-out advice originally promoted by the Apple folks last year (“You don’t need assembler, the compiler can do better than handwritten assembly” or words to that effect), it hit me with particular irony. You see, the lack of adequate compiler tools (Thanks, Apple, for your inimitable support here) has forced me to write more assembly code for the 601 in the last couple months than for all other computers combined over the previous decade. Anyway I read his article with great interest. Some comments:

1. Perhaps your readers should know that the sequence,

    addis  r3,0,0xABCD
    addi   r3,0,0xEF23

is unlikely to load the hex value ABCDEF23 into r3, for two reasons. First of all, the result of the addis instruction will be discarded by the second, since it sums ZERO + EF23, not the previous result. Better to use r3 as the second parameter. But it still won’t work, because addi takes a SIGNED immediate operand, and EF23 sign-extends to FFFFEF23, not 0000EF23, which adds -1 to the previously loaded upper half. The correct sequence for loading ABCDEF23 into r3 is:

    addis  r3,0,0xABCE
    addi   r3,r3,0xEF23 or alternatively,

    addi   r3,0,0xEF23
    addis  r3,r3,0xABCE

or still better, because it’s more understandable (ori takes an UNsigned operand):

    addis  r3,0,0xABCD
    ori    r3,r3,0xEF23

2. I’m not sure how Bill intends to use the -ze variants for add and subtract “as register-to-register move or negate and move mnemonics” but he’s likely to be surprised when he tries to do so and finds the previous contents of the carry flag (XER.CA) randomizing his results somewhat. Better to stick to ORI for move, and NEG for negate and move.

3. Bill tells us that “Divide operations treat rA as a 64-bit dividend...” Perhaps somebody should tell Motorola, because their manual reports the much more reasonable proposition that the dividend is 32 bits. If it’s 64, where do the other 32 bits come from?

4. It’s really too bad we are stuck with the IBM syntax for the rotate operators. Or I should say YOU are stuck with it: very early on I realized I was, like Bill, burning a lot of time on this stuff, and altered my assembler and disassembler to reflect what is REALLY going on. All three of the rotates have very simple semantics: they rotate the source operand left n bits, then replace some bits in the destination with the rotated bits under the control of a mask. The remaining bits are either zeroed or left unchanged (the fundamental difference between the rlwimi and rlwinm). The problem is specifying the mask. See how much simpler these two instructions are to read:

    rotm    r29,r27,#3,=0007FFF8  ; rotate left 3, replace indicated 
bits
    rotz    r6,r15,#1,=00000080   ; rotate left 1, pick out a single 
bit

when compared to:

    rlwimi  r29,r27,3,13,28
    rlwinm  r6,r15,1,24,24

5. The latency figures Bill gives for branch instructions are likely to be misleading - perhaps this is why everybody makes the case for compilers being better. Branches are free if you give them enough setup time, basically three integer instructions after the one that altered the CR or CTR or LR register the branch depends on, but a sequence of branches with no data dependencies has a different kind problem. After a sequence of integer operations, the fourth consecutive branch not taken will introduce a bubble in the pipeline, for an effective 1 cycle delay. Consecutive branches taken cost two cycles each; they become free only if two or more integer operations separate each pair of branches taken. Then there are boundary conditions, but these three rules make for pretty efficient code.

6. I think Bill temporarily forgot that IBM numbers the 601 bits Big-Endian when he illustrated the mtcrf instruction. If CRM = 0x08, then it’s cr4 (not cr3) that is replaced with bits 16-19 (not 12-15). He got the visual image correct, but he would be surprised when he went to use the bits by number. Another argument for the superiority of a visual mask over bit numbers. And yes, my assembler lets me use a visual mask syntax here as in the rotates. Perhaps somebody will come up with a macro preprocessor for the MPW assembler to parse the bit image syntax into something the assembler understands.

- Tom Pittman, Itty Bitty Computers

Bill Karsh responds I am grateful to Tom Pittman for scrutinizing my article in such detail, and pleased that the readers and I will benefit from the corrections. I agree with Tom on most of his points, but let me respond to each.

0) High Level vs. Assembly programming - To everybody (not just Tom who hates tired dogma) maybe I was not clear enough on my personal feelings about assembly. First of all, there is absolutely no question that just about anything coded in (good) PPC assembly can beat the pants off the best compiler yet available and probably ever likely to be available. I never could have intended otherwise. In fact, I code in assembly myself, but my particular work demands peak performance for a handful of core operations. It takes a great deal of effort to achieve this, and one can always improve the code by small changes here and there in a never ending process of refinement. If your particular job specification is to speed up existing and otherwise correct code, you can do much in C, but you can always do more in assembly by paying the price of being absolutely tied to machine-specific code. That’s fine if you think it’s worth the time that could be spent writing new, more portable and maintainable code. Yes, sometimes it is worth it. The optimization should be well targeted in any case.

What I wanted to argue about compilers was that the capability is there in the hardware to ease the compiler writer’s job of optimizing. It ought to be possible for compilers to do better than they do today at PPC code and better at PPC code than they have ever been at 68K code. Since there is so much for you to do just to get your project on its feet, personally optimizing things should be a lower priority than making them correct and meeting specs. You will gain (some) optimization implicitly as the compilers improve, and there is some reason to be optimistic about this happening. Don’t forget that as the machines get faster, the need for touch-ups keeps diminishing. There will always be a place for some killer assembly or some compiler hand-holding, but the genuine need should not arise as often as it used to. A blanket statement about assembly or optimization being evil would just be foolish.

1) Loading 0xABCDEF23 into a register - Tom is correct. My example is the result of hastily copying notes from place to place and incurring typos, for which I have no excuse. Each of his examples of loading a long literal constant is correct.

2) Clever uses of addze and subze as moves - Of course, the carry bit would have to be cleared for the moves to work as suggested by me. Tom is right again. If writing one’s own assembly, his are preferred methods for effecting the moves reliably. Otherwise, the ze instructions should really only be employed for extended arithmetic.

3) The sizes of divw rD, rA, rB operands and results - I have no argument with Tom here either. The numerator (N), denominator (d) and quotient (Q) are all 32-bit quantities. When I said what I did about N being treated as 64-bits, I was merely likening the division to that familiar in the 68K divs.w instruction, where N is exactly twice the width of the d or Q registers. I intended that you might consider N in your mind as extended in this way as a formal convenience, not that the hardware operates this way.

4) Shift and rotate semantics - I think Tom is saying that he has created some simplifying macros for himself, which can only be lauded. However, I was concerned in the article with interpreting what most users are likely to see in their standard disassembler’s output.

5) Branch timing - I agree only in spirit. There is much to say about branch timing. I reported a latency of one cycle for branch execution which is generally true - that’s how long a branch takes to execute (in vacuum, so to speak). This gives little hint that a variety of things can happen depending on the context of the branch. I take issue with Tom’s trying to characterize timing based on the language of branches taken or not taken. Those are the rules for 68K branch timing. On the PPC that is too simplistic. Branch timing is mainly governed by whether branches are correctly or incorrectly predicted. Incorrectly predicted branches hurt something awful, causing the IQ to be flushed, everything contingently executed to be flushed and new instructions to be fetched. This can cause a delay of more than one or two cycles. Further, the BPU handles one branch at a time, which is why stacking them up is a no-no. The rules for employing branching to best advantage are complicated - too much so to be meaningfully summarized in the space of a letter.

6) mtcrf mask bits - Yep, I mistakenly reversed the bit numbering in the CRM mask parameter. The left-most bit of CRM corresponds to the left-most CR field (cr0) and similarly the right-most bit <-> right-most field (cr7). Whoops!

Let me elaborate on one thing that can be confusing and that occurs frequently in code. The extsb (sign extend byte) instruction extends to a width of 32-bits, unlike the ext.b 68K instruction which extends a byte to 16 bits. This behavior is in keeping with the idea that PPC arithmetic instructions act in general on all the whole of a register.

If anything else is annoying or just plain wrong in the presentation, let me hear about it.

- billKarsh@aol.com

OpenDoc, OLE, and Real Developers

I have just received Microsoft’s OLE SDK (free of charge) and been browsing it. There is a lot of marketing (evangelizing?) stuff in it, including some “deep” technical comparations between OLE and OpenDoc. If you program the Macintosh, your future is OpenDoc - Apple says.

Well, Microsoft has different plans. If you program for OLE, which is available now, and it’s free of charge, you can port your components to Windows and you can work with Excel or Word now - B. Gates says. After much reading and studying I came to a conclusion. I will support OpenDoc because frankly I don’t care nor like Windows and I do vertical apps for Macs and UNIX, but if I was a mainstream developer I would go for OLE.

There are some technical differences. According to MS, OLE is a superior technology now and it will get better in the future. OpenDoc has several technical merits but, alas, it’s not yet available. OpenDoc has a HUGE advantage too: It’s open, and that means that source code is available and it’s going to be ported from PDAs to Mainframes. Microsoft says that OLE is cross-platform (Win-Mac) now and it’s true, and it says it will run under UNIX for free only if you licence (surprise) its Win32 API!!! And they call that Open. Please don’t make me laugh.

I would like to see some input about ISD future plans on this technologies and some technical comparisons too.

So, take a pick, because we are going to start coding “parts” and putting them together like chips in a computer.

- Daniel Nofal TecH S.A Buenos Aires, ARGENTINA

Dylan Takes A Load Off

Thanks for the Sept. Dylan article. I was disappointed, though, that the article didn’t use the example code to emphasize what makes Dylan different from C++ and other static languages. I’m not sure how many readers would wade through the code to discover the link between the interface definition of the OpenMovieFile function:

function “OpenMovieFile”, output-argument: resRefNum;

and its invocation in the open-movie-file method:

let (err,ref-num) = OpenMovieFile(spec, file.data-permission);

nor notice some of the pleasures of Dylan they illustrate. err and ref-num didn’t have to be declared prior to their use - Dylan figured it out from the context and created the properly-typed objects. OpenMovieFile() is returning multiple values. The developer didn’t have to concern herself whether arguments should be passed by value or by reference, nor worry about the intricacies of memory management because Dylan has automatic garbage collection.

- Steve Palmen, tshirt2b@halcyon.com

 
AAPL
$97.67
Apple Inc.
+0.64
MSFT
$44.50
Microsoft Corpora
+0.10
GOOG
$589.02
Google Inc.
-4.33

MacTech Search:
Community Search:

Software Updates via MacUpdate

TinkerTool 5.3 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more
Audio Hijack Pro 2.11.0 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Intermission 1.1.1 - Pause and rewind li...
Intermission allows you to pause and rewind live audio from any application on your Mac. Intermission will buffer up to 3 hours of audio, allowing users to skip through any assortment of audio... Read more
Autopano Giga 3.6 - Stitch multiple imag...
Autopano Giga allows you to stitch 2, 20, or 2,000 images. Version 3.0 integrates impressive new features that will definitely make you adopt Autopano Pro or Autopano Giga: Choose between 9... Read more
Airfoil 4.8.7 - Send audio from any app...
Airfoil allows you to send any audio to AirPort Express units, Apple TVs, and even other Macs and PCs, all in sync! It's your audio - everywhere. With Airfoil you can take audio from any... Read more
Microsoft Remote Desktop 8.0.8 - Connect...
With Microsoft Remote Desktop, you can connect to a remote PC and your work resources from almost anywhere. Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help... Read more
xACT 2.30 - Audio compression toolkit. (...
xACT stands for X Aaudio Compression Toolkit, an application that encodes and decodes FLAC, SHN, Monkey’s Audio, TTA, Wavpack, and Apple Lossless files. It also can encode these formats to MP3, AAC... Read more
Firefox 31.0 - Fast, safe Web browser. (...
Firefox for Mac offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals... Read more
Little Snitch 3.3.3 - Alerts you to outg...
Little Snitch gives you control over your private outgoing data. Track background activityAs soon as your computer connects to the Internet, applications often have permission to send any... Read more
Thunderbird 31.0 - Email client from Moz...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more

Latest Forum Discussions

See All

Reddme for iPhone - The Reddit Client (...
Reddme for iPhone - The Reddit Client 1.0 Device: iOS iPhone Category: News Price: $.99, Version: 1.0 (iTunes) Description: Reddme for iPhone is an iOS 7-optimized Reddit client that offers a refreshing new way to experience Reddit... | Read more »
Jacob Jones and the Bigfoot Mystery : Ep...
Jacob Jones and the Bigfoot Mystery : Episode 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Jacob Jones is back in Episode 2 of one of Apples 'Best of 2013' games and an App Store... | Read more »
New Trailer For Outcast Odyssey, A New K...
New Trailer For Outcast Odyssey, A New Kind of Card Battler Posted by Jennifer Allen on July 25th, 2014 [ permalink ] Out this Fall is a new kind of card battle game: Outcast Odyssey. | Read more »
Garfield: Survival of the Fattest Coming...
Garfield: Survival of the Fattest Coming to iOS this Fall Posted by Jennifer Allen on July 25th, 2014 [ permalink ] Who loves lasagna? Me. Also everyone’s favorite grumpy fat cat, Garfield. | Read more »
Happy Flock Review
Happy Flock Review By Andrew Fisher on July 25th, 2014 Our Rating: :: HERD IT ALL BEFOREUniversal App - Designed for iPhone and iPad Underneath the gloss of Happy Flock’s visuals is a game of very little substance. It’s cute, but... | Read more »
Square Register Updates Adds Offline Pay...
Square Register Updates Adds Offline Payments Posted by Ellis Spice on July 25th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Looking For Group – Hearthstone’s Curse...
For the first time since its release (which has thankfully been a much shorter window for iPad players than their PC counterparts), Blizzard’s wildly successful Hearthstone: Heroes of Warcraft CCG is sporting some brand new content: the single... | Read more »
Poptile Review
Poptile Review By Jennifer Allen on July 25th, 2014 Our Rating: :: SIMPLY FUNUniversal App - Designed for iPhone and iPad Simple yet a little bit glorious, Poptile is a satisfying entertaining puzzle game with oodles of the ‘one... | Read more »
Modern Combat 5: Blackout Review
Modern Combat 5: Blackout Review By Brittany Vincent on July 25th, 2014 Our Rating: :: LESS QQ, MORE PEW PEWUniversal App - Designed for iPhone and iPad The fifth entry into the blockbuster Modern Combat series is what mobile... | Read more »
Watch and Share Mobile Gameplay Videos W...
Watch and Share Mobile Gameplay Videos With Kamcord Posted by Jennifer Allen on July 25th, 2014 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »

Price Scanner via MacPrices.net

iMacs on sale for $150 off MSRP, $250 off for...
Best Buy has iMacs on sale for up to $160 off MSRP for a limited time. Choose free home shipping or free instant local store pickup (if available). Prices are valid for online orders only, in-store... Read more
Mac minis on sale for $100 off MSRP, starting...
Best Buy has Mac minis on sale for $100 off MSRP. Choose free shipping or free instant local store pickup. Prices are for online orders only, in-store prices may vary: 2.5GHz Mac mini: $499.99 2.3GHz... Read more
Global Tablet Market Grows 11% in Q2/14 Notwi...
Worldwide tablet sales grew 11.0 percent year over year in the second quarter of 2014, with shipments reaching 49.3 million units according to preliminary data from the International Data Corporation... Read more
New iPhone 6 Models to Have Staggered Release...
Digitimes’ Cage Chao and Steve Shen report that according to unnamed sources in Apple’s upstream iPhone supply chain, the new 5.5-inch iPhone will be released several months later than the new 4.7-... Read more
New iOS App Helps People Feel Good About thei...
Mobile shoppers looking for big savings at their favorite stores can turn to the Goodshop app, a new iOS app with the latest coupons and deals at more than 5,000 online stores. In addition to being a... Read more
Save on 5th generation refurbished iPod touch...
The Apple Store has Apple Certified Refurbished 5th generation iPod touches available starting at $149. Apple’s one-year warranty is included with each model, and shipping is free. Many, but not all... Read more
What Should Apple’s Next MacBook Priority Be;...
Stabley Times’ Phil Moore says that after expanding its iMac lineup with a new low end model, Apple’s next Mac hardware decision will be how it wants to approach expanding its MacBook lineup as well... Read more
ArtRage For iPhone Painting App Free During C...
ArtRage for iPhone is currently being offered for free (regularly $1.99) during Comic-Con San Diego #SDCC, July 24-27, in celebration of the upcoming ArtRage 4.5 and other 64-bit versions of the... Read more
With The Apple/IBM Alliance, Is The iPad Now...
Almost since the iPad was rolled out in 2010, and especially after Apple made a 128 GB storage configuration available in 2012, there’s been debate over whether the iPad is a serious tool for... Read more
MacBook Airs on sale starting at $799, free s...
B&H Photo has the new 2014 MacBook Airs on sale for up to $100 off MSRP for a limited time. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.