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

TrailRunner 3.8.1840 - Route planning fo...
TrailRunner is the perfect companion for runners, bikers, hikers, and all people wandering under the sky. Plan routes on a geographical map. Import GPS or workout recordings and journalize your... Read more
NetShade 7.1 - Browse privately using an...
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
1Password 6.8.2 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
ClamXav 2.15.1 - Virus checker based on...
ClamXav is a popular virus checker for OS X. I have been working on ClamXav for more than 10 years now, and over those years, I have invested a huge amount of my own time and energy into bringing... Read more
NetShade 7.1 - Browse privately using an...
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
1Password 6.8.2 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
TrailRunner 3.8.1840 - Route planning fo...
TrailRunner is the perfect companion for runners, bikers, hikers, and all people wandering under the sky. Plan routes on a geographical map. Import GPS or workout recordings and journalize your... Read more
ClamXav 2.15.1 - Virus checker based on...
ClamXav is a popular virus checker for OS X. I have been working on ClamXav for more than 10 years now, and over those years, I have invested a huge amount of my own time and energy into bringing... Read more
Vienna 3.1.15 :9729aef5: - RSS and Atom...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more
Vienna 3.1.15 :9729aef5: - RSS and Atom...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more

Thimbleweed Park (Games)
Thimbleweed Park 1.0.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.0 (iTunes) Description: A brand new adventure game from Ron Gilbert and Gary Winnick, creators of the classics Monkey Island and Maniac Mansion!... | Read more »
The best simulation games on mobile
There's nothing like a good sim -- from the seemingly ridiculous to the incredibly mundane, you can be there's a simulation game out there for your every whim. [Read more] | Read more »
INKS guide - how to create works of pinb...
INKS puts a clever new spin on everyone's favorite classic arcade game, pinball. The core mechanics are the same -- keep a little ball pinging around the board for as long as possible without letting it fall into the precarious holes in the board.... | Read more »
Warbands: Bushido (Games)
Warbands: Bushido 1.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: Warbands:Bushido is a miniatures board game with cards, miniatures, dice and beautiful terrains to fight on, with both... | Read more »
The best mobile games like Divinity: Ori...
Divinity: Original Sin 2 launched this week to the excitement of RPG fans everywhere. The game, which derives a lot of of its story and mechanics from old-school isometric RPGs and Dungeons & Dragons, has unseated PlayerUnknown's... | Read more »
Iron Marines guide - beginner tips and t...
Iron Marines is a brilliant RTS title that feels a bit like Starcraft. It's got a sci-fi setting and some of the most spectacular strategy mechanics we've seen in mobile games to date. With that said, the RTS genre can be a bit tricky to break... | Read more »
The best new games we played this week -...
The work week can be tough, but on the bright side, it's almost overandthere are bunches of brand new games to try out this weekend. This week definitely makes up for last week's sleepiness ten-fold. We've got one of the finest RTS game on mobile... | Read more »
Through the Ages (Games)
Through the Ages 1.0.60 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.60 (iTunes) Description: The offical adaptation of Vlaada Chvátil’s strategy classic, the second best board game ever by Board Game Geek website... | Read more »
The best RTS games like Iron Marines
Iron Marines launched today, and it's definitely taking the mobile gaming world by storm. In fact, our reviews editor Campbell says it's "quite possibly the best real-time strategy game on the App Store." If you're looking for more real-time... | Read more »
Uri: The Sprout of Lotus Creek (Games)
Uri: The Sprout of Lotus Creek 1.0.5 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.5 (iTunes) Description: Published by Fantastic Games IntroductionDesigned by DreamTree Games(An indie games studio in Malaysia ) | Read more »

Price Scanner via MacPrices.net

Apple refurbished 128GB iPhone 6s and 6s Plus...
Apple has Certified Refurbished 128GB iPhone 6s and 6s Plus’ available for up to $100 off the price of new models. Space Gray, Silver, Gold, and Rose Gold models are available. Each phone comes... Read more
13-inch 2.3GHz Silver MacBook Pros on sale fo...
B&H Photo has 2017 13″ 2.3GHz Silver MacBook Pros in stock today and on sale for $100 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Silver... Read more
12-inch 64GB iPad Pros available for $749, $5...
MacMall has 12″ 64GB iPad Pros on sale for $749 including free shipping. Their price is $50 off MSRP. Read more
Sunday deal: 10-inch 256GB iPad Pros for $699...
MacMall has 10.5″ 256GB WiFi iPad Pros on sale today for $699 including free shipping. That’s $100 off MSRP. Read more
2017 12-inch 1.2GHz Retina MacBooks on sale f...
Amazon has 2017 12″ 1.2GHz Retina MacBooks on sale for $100 off MSRP. Shipping is free: 12″ 1.2GHz Space Gray MacBook: $1199 $100 off MSRP 12″ 1.2GHz Silver MacBook: $1199 $100 off MSRP 12″ 1.2GHz... Read more
Apple Certified Refurbished 21-inch and 27-in...
Apple is now offering a full line of Certified Refurbished 2017 21″ and 27″ iMacs. Models start at $1019 and range up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is... Read more
Apple now offering Certified Refurbished 2017...
Apple is now offering Certified Refurbished 2017 12″ Retina MacBooks for up to $240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free... Read more
Steve Jobs’ Democratization Of The Smartphone...
Can it be only ten years since Steve Jobs introduced the world to the iPhone and changed everything? Jobs and Apple didn’t invent the smartphone. IBM designed a primitive one called SIMON in 1992,... Read more
Save up to $200 on 2017 Apple iMacs
B&H Photo has 2017 21-inch and 27-inch iMacs in stock and on sale for $100-$200 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $... Read more
AnyTrans 6.0 Lets Android Users Switch to New...
iMobie has announced the release of their flagship product AnyTrans V6.0 with free iOS Mover. Available for both Mac and Windows, now users are completely free to transfer most types of Android data... Read more

Jobs Board

*Apple* Data Center Site Selection and Strat...
Job Summary As Apple 's products and services scale the globe, the Data Center Affairs team works behind the scenes to secure infrastructure for Apple 's data Read more
*Apple* Professional Learning Specialist - A...
Job Summary The Apple Professional Learning Specialist is a full-time position for one year with Apple in the Yuma, AZ area. This position requires a high Read more
Lead *Apple* Solution Consultant - Apple In...
…develop a team of diverse partner employees focusing on excellence to deliver the Apple story. Even when you're not present, you will maintain a consistent influence Read more
Product Manager, *Apple* News - Apple Inc....
Job Summary The Product Manager, Apple News will assist in defining and marketing new features, media types, products, and services as part of the Apple News Read more
watchOS Frameworks Engineering Manager, *App...
Job Summary Join the team that is shaping the future of software development for Apple Watch! Apple is looking for an exceptional software engineering leader to Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.