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

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

CrossOver 14.1.3 - Run Windows apps on y...
CrossOver can get your Windows productivity applications and PC games up and running on your Mac quickly and easily. CrossOver runs the Windows software that you need on Mac at home, in the office,... Read more
Little Snitch 3.5.3 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
OmniGraffle Pro 6.2.3 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniFocus 2.2 - GTD task manager with iO...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
Cocktail 8.4 - General maintenance and o...
Cocktail is a general purpose utility for OS X 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
PDFKey Pro 4.3 - Edit and print password...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Kodi 15.0.beta1 - Powerful media center...
Kodi (was XBMC) is an award-winning free and open-source (GPL) software media player and entertainment hub that can be installed on Linux, OS X, Windows, iOS, and Android, featuring a 10-foot user... Read more
DiskCatalogMaker 6.4.12 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more
Macs Fan Control 1.3.0.0 - Monitor and c...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more
Lyn 1.5.11 - Lightweight image browser a...
Lyn is a lightweight and fast image browser and viewer designed for photographers, graphic artists and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it... Read more

Battle of Gods: Ascension (Games)
Battle of Gods: Ascension 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: TURN-BASED TACTICAL COMBATFight tactical battles against the forces of Hades! In Battle of Gods: Ascension you play... | Read more »
Shadowmatic's Latest Update Adds a...
Shadowmatic's shadowy shadow-ness is getting a little shadowy-er thanks to a recent update that adds an Arcade Mode. [Read more] | Read more »
Sunrise Calendar and Slack Have Assimila...
Wunderlist is perhaps one of the most populat and beloved productivity apps on the App Store - and now it's gone and incorporated itself into other useful services like Sunrise Calendar and Slack. [Read more] | Read more »
Crossy Road Devs Hipster Whale are Bring...
Hipster Whale, the minds behind the rather popular (and rather great) Crossy Road, have teamed-up with Bandai Namco to create PAC-MAN 256: an absolutely bonkers looking maze runner chaser thing. | Read more »
Meet the New Spotify Music
Spotify Music  has a lot going on. They're introducing 3 new modes to serve all your musical needs, with the "Now" start page  gives you curated playlists based on your particular tastes. As you listen the app will learn more about your tastes and... | Read more »
What the Apple Watch Gets Right, and Wha...
| Read more »
Celebrate PAC-MAN's 35th Birthday W...
BANDAI NAMCO Entertainment America is celebrating PAC-MAN's 35th anniversary by releasing updates for PAC-MAN and PAC-MAN Lite for iOS. [Read more] | Read more »
Strike Wing Episode 2 has Landed on the...
Strike Wing: Raptor Rising is an exciting space combat simulator by Crescent Moon Games, which was recently updated to continue the story with Episode 2. [Read more] | Read more »
Kiqplan Expands its Interactive Coaching...
The makers of Fitbug have been hard at work on their Kiqplan lineup, and have added four new summer themed plans to help you get the most out of your workout. [Read more] | Read more »
Make a Photobook in Minutes with Pictyea...
What happens when you can't stop taking photos and have an urge to create a photobook? Pictyear saves the day. [Read more] | Read more »

Price Scanner via MacPrices.net

What Would the ideal Apple Productivity Platf...
For the past four years I’ve kept a foot in both the Mac and iPad camps respectively. my daily computing hours divided about 50/50 between the two devices with remarkable consistency. However, there’... Read more
PageMeUp 1.2.1 Ten Dollar Page Layout Applica...
Paris, France-based Softobe, an OS X software development company, has announced that their PageMeUp v. 1.2.1, is available on the Mac App Store for $9.99. The license can be installed on up to 5... Read more
Eight New Products For USB Type-C Application...
Fresco Logic, specialists in advanced connectivity technologies and ICs, has introduced two new product families targeting the Type-C connector recently introduced across a number of consumer... Read more
Scripps National Spelling Bee Launches Buzzwo...
Scripps National Spelling Bee fans can monitor the action at the 2015 Spelling Bee with the new Buzzworthy app for iOS, Android and Windows mobile devices. The free Buzzworthy app provides friendly... Read more
13-inch 2.5GHz MacBook Pro on sale for $120 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $979 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price for this model (except for Apple’... Read more
27-inch 3.3GHz 5K iMac on sale for $1899, $10...
B&H Photo has the new 27″ 3.3GHz 5K iMac on sale for $1899.99 including free shipping plus NY tax only. Their price is $100 off MSRP. Read more
Save up to $50 on iPad Air 2, NY tax only, fr...
B&H Photo has iPad Air 2s on sale for up to $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
New 13-inch 2.9GHz Retina MacBook Pro on sale...
B&H Photo has the 13″ 2.9GHz/512GB Retina MacBook Pro on sale for $1699.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price for this model from... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2014 MacBook Airs available starting at $679. An Apple one-year warranty is included with each MacBook, and shipping is free: - 11″ 1.4GHz/128GB... Read more

Jobs Board

Senior Software Engineer - *Apple* SIM - Ap...
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
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
Architect / Senior Software Engineer, *Apple...
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
*Apple* Pay Support Readiness Project Manage...
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
Hardware Design Validation Engineer - *Apple...
**Job Summary** The Apple Watch team is looking for a Hardware Design Validation Engineer. This person will be part of the Apple Watch hardware team with Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.