TweetFollow Us on Twitter

May 94 Cornfield
Volume Number:10
Issue Number:5
Column Tag:From The Corn Field

Thoughts From The Cornfield

Provocative, perhaps inflammatory, but just say no to assembly language on PowerPC

By Steve Kiene, MindVision Software, Lincoln, Nebraska

About the author

Steve, author of things like Stacker for Macintosh, cares about performance, code size, performance, portability, and performance as much as anyone we know (well, there’s always Mike Scanlin, too). Steve’s recently worked through a number of issues about porting to the PowerPC for performance, and along the way surprised himself with his conclusions. He’s curious about your reaction, so please let us know if they surprise you, too. I can just see our assistant Al holding up a placard with this in big letters: editorial@xplain.com

Writing code in assembly language instead of a high-level language to get performance is fast becoming an historic anachronism. The fierce competition in the 90’s leads to time-to-market battles that cannot be won by the company that insists on writing large chunks of their product in assembly language.

I’ve seen plenty of code whose authors have spent an inordinate amount of time tweaking assembly language instructions to get the most speed out of the code when the real problem was a slow algorithm. It’s the old problem of not seeing the forest for the trees. Careful examination of the algorithm offers more potential for improved performance than coding a bad algorithm in tightly-tuned assembly language. This generally holds true even when the improved algorithm is coded in C.

I took some code a friend had written; he had spent weeks hand-tuning assembly code. I re-examined the algorithms and found a better way to do it. I coded it up in C and the new C code ran fifty times faster on the 68K than the assembly solution had before. Now, it not only performs, it’s portable and more maintainable. After simply recompiling the code for Power Macintosh, its speed doubled. To convert the assembly code would have taken at least a couple of weeks for someone proficient not only in writing PowerPC assembly code, but also good at scheduling the assembly instructions to keep the chip as busy as possible.

Now, with all that said, there are reasons for writing PowerPC assembly language. So, if you have to write part of your program in assembly, make sure it’s the right part and be completely sure you cannot increase the speed by improving the algorithm. There’s little sense in writing assembly language for code that only amounted to 4% of the execution time, but it’s not that hard to find programs that do just that. What was gained by writing the code in assembly language rather than a high-level language?

The release of the Power Macintosh machines has sent many 68K assembly language programmers scrambling to learn the new architecture and its assembly language so that they can continue to performance-program the Macintosh. However, as they are finding out, programming in PowerPC assembly language is much harder than on the 68K Macintosh.

I’ve seen several examples of PowerPC assembly language code that at first glance looks fast but after careful examination the code turns out to run slower than expected. RISCprocessors require understanding the architecture of both the CPU and the memory bus to get good performance, and it’s simply difficult to keep all of the rules and constraints in your head while trying to be creative and write code. Compilers, on the other hand, just don’t care how many rules they have to remember.

Reasons to avoid assembly language

(1) Assembly language code is not easily ported to different instruction set architectures. There are tools which will port 68K assembly to PowerPC assembly, but you run the risk that the architectures are so different a port doesn’t get you the full potential of the new architecture.

(2) Code can be written in a shorter amount of time in a high level language than it can be in assembly. People want to argue this, claiming that bit manipulation routines are too hard to do in C, but it’s just not true. I suspect that if they knew C as well as they knew assembler there would be little or no argument.

(3) It is far easier to make mistakes in assembly than it is in a high level language. High level languages offer abstraction and structure which makes many common assembly language problems simply non-existent.

(4) Code written in assembly is harder to maintain both for the original programmer as well as a different programmer. Because of the fine-grain control you get with assembly language, it is not always easy to follow the flow of the code.

(5) The development tools available for writing assembly language are not advancing at the same rate as those for high level languages. In fact, there are many situations where the tools are getting worse. Apple’s PowerPC Assembler for MPW is not nearly as sophisticated as their 68K Assembler.

Reasons to use assembly language

(1) Highly time-critical code, such as software which interfaces with a piece of hardware which has very specific timing dependencies. Not very common.

(2) Code where space is at a minimum, such as embedded controllers. Generally not applicable to the Macintosh.

(3) Code that is proven to be an unacceptable bottleneck in a specific task.

(4) Places where parameters are passed in specific locations that are not easily accessible to a high level language. [Between the PowerPCruntime architecture, and the protocol conversion that Mixed Mode does for you, this problem essentially goes away on the Power Macintosh - Ed stb]

In all of these instances, there is a need for assembly only in specific places in the code. There is no need to code large parts in assembly.

How to speed up your code - the old way

The most common way to speed up existing code is to find the parts of the program that are slow and rewrite them in assembly. In the past that may have been a good way to gain more speed. Today, that model is not only outdated, it can backfire. I’ve seen people rewrite their code in PowerPC assembly language only to see it run SLOWER. Do not assume you know more about the processor architecture than the compiler. Unless you understand the instruction scheduling of the processor entirely, you probably can’t out-do a good compiler.

How to speed up your code - the new way

Determine which parts of your program are used the most. If a particular feature takes several minutes to run but is only used once a month, maybe it’s not as important as features which takes ten seconds but are used every five minutes. Watch your customers’ usage patterns. Ask them which parts of the program are annoyingly slow. Ask them why they think those parts are slow. Remember, slowness is subjective. What is slow to a power user may seem perfectly fine to a novice user. Who uses your product, the novice or the power user?

Once you have identified the areas of your software that seem slow, you may want to back up the results with scientific data. Run performance analysis tools to see exactly where in the code things are slow when you perform the tasks that users said were slow. THINK C and CodeWarrior have performance monitoring tools included that work well. MPW has its own performance tools which are adequate. If you are writing code that is not easily interfaced to these tools, I recommend you look at the source code provided for the performance tools in THINK C. It is very easy to adapt this code to monitor the performance of any piece of code.

One thing to remember is that the performance of your software may differ greatly when comparing Power Macintosh to the 68K Macintosh. Performance may also vary quite a bit between specific Macintosh models. Machines with a 32 bit data bus will perform memory intensive operations much faster than machines with a 16 bit data bus.

Now that you have figured out which parts of your program are slow, it is time to decide how to make them faster. The first thing to do is to examine the underlying algorithms of the code. Is there anything fundamental that you can do to speed things up? For example, if you are performing a text search, how do you search through the text? Do you use Munger? Perhaps something like a Boyer-Moore algorithm would be much faster. Remember, the key is to work smarter. Brute force is not the answer - it’s a matter of brains over brawn.

Sometimes simply a small change to your existing algorithm will make things much faster. I sped up a search algorithm I wrote years ago by a factor of three by simply adding two lines of code. Look at your algorithm and examine how it operates with common data that goes through it. Perhaps certain shortcuts can be taken when the most common data runs through it.

If you don’t have many books on fundamental computer algorithms, now is the time to stock up. I am a firm believer that you cannot have enough books on algorithms. At the end of this article I have listed several books that will help broaden and round out your algorithm skills. I highly recommend all of them.

Once you have analyzed the specific parts of your program that are bottlenecks, it is time to look at the architecture of your program as a whole. If your program is rather large you may want to look at it as several modules working together.

Is the underlying architecture of your program going to be a bottleneck? Are there time consuming tasks that can be done in the background at idle time rather than being done while the user must wait? Are you doing network communication synchronously when you could do it asynchronously and give the user their machine back? Are there tasks that need to be performed but don’t need to give immediate feedback to the user? These kinds of tasks are good candidates for idle time processing, additional user feedback, modeless dialog boxes, asynchronous programming, and other methods of helping the user feel as if they are not waiting on your program, or at least aren’t prevented from doing something else while you get your thing done. If you keep the user occupied or help them feel productive while your program is working, they’ll be more patient with whatever performance you have.

How to write the code in Assembly Language

If, after careful examination, you have determined a bottleneck in your program, analyzed the algorithms as best you can, rewritten them to be as efficient as possible, and still it is not fast enough, perhaps it is time to code a small part in assembly. The best place to start is to disassemble compiler- generated code for the routine you want to code in assembly. Look at the code. What is inefficient about it? Are registers constantly being reloaded? Are the registers being used efficiently? Are the instructions scheduled for maximum pipelining? Very often you can take the disassembled code, make a few minor modifications to it and see a very nice speed increase.

Perform accurate timing tests on the code you are optimizing. Unless you completely understand the PowerPC Architecture Manual and the PowerPC 601 User’s Guide, more often than not you will make PowerPC code slower than a good compiler. The bottom line is that it must run faster, not look faster.

Maintain an exact high-level equivalent of the assembly code, and keep it right there in the same file. This way if you port your code to a different architecture, you’ve got what you need to get up and running quickly. In many cases the bottleneck on one machine will not be a bottleneck on another.

In Conclusion

This article has discussed some alternate methods of speeding up your program execution that are in many ways better than traditional methods used by many programmers. The goal is to maximize your gain and minimize your effort. By working smarter rather than harder, you can have a faster program in less time.

Recommended Books

[1] Thomas H. Cormen, Charles E. Leiserson, and Ronald L. Rivest. Introduction to Algorithms. MIT Press, 1990.

[2] Alfred V. Aho, John E. Hopcroft, and Jeffrey D. Ullman. The Design and Analysis of Computer Algorithms. Addison-Wesley, 1974.

[3] Saumyendra Sengupta and Paul Edwards. Data Structures in ANSI C. Academic Press, 1991.

[4] Donald Knuth. The Art of Computer Programming, Volumes 1-3. Addison-Wesley, 1973

[5] Daniel H. Greene and Donald E. Knuth. Mathematics for the Analysis of Algorithms., Third Edition Birkhäuser, 1990.

[6] P. D. Eastman. Go, Dog, Go! Random House, 1961.

[7] Manoochehr Azmoodeh. Abstract Data Types and Algorithms, Second Edition. Macmillan, 1990.

 
AAPL
$102.50
Apple Inc.
+0.25
MSFT
$45.43
Microsoft Corpora
+0.55
GOOG
$571.60
Google Inc.
+2.40

MacTech Search:
Community Search:

Software Updates via MacUpdate

Skype 6.19.0.450 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
LibreOffice 4.3.1.2 - Free Open Source o...
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
SlingPlayer Plugin 3.3.20.505 - Browser...
SlingPlayer is the screen interface software that works hand-in-hand with the hardware inside the Slingbox to make your TV viewing experience just like that at home. It features an array of... Read more
Get Lyrical 3.8 - Auto-magically adds ly...
Get Lyrical auto-magically add lyrics to songs in iTunes. You can choose either a selection of tracks, or the current track. Or turn on "Active Tagging" to get lyrics for songs as you play them.... Read more
Viber 4.2.2 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device,... Read more
Cocktail 7.6 - 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
LaunchBar 6.1 - Powerful file/URL/email...
LaunchBar is an award-winning productivity utility that offers an amazingly intuitive and efficient way to search and access any kind of information stored on your computer or on the Web. It provides... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more

Latest Forum Discussions

See All

Rhonna Designs Magic (Photography)
Rhonna Designs Magic 1.0 Device: iOS Universal Category: Photography Price: $1.99, Version: 1.0 (iTunes) Description: Want to sprinkle *magic* on your photos? With RD Magic, you can add colors, filters, light leaks, bokeh, edges,... | Read more »
This Week at 148Apps: August 25-29, 2014
Shiny Happy App Reviews   | Read more »
Qube Kingdom – Tips, Tricks, Strategies,...
Qube Kingdom is a tower defense game from DeNA. You rally your troops – magicians, archers, knights, barbarians, and others – and fight against an evil menace looking to dominate your kingdom of tiny squares. Planning a war isn’t easy, so here are a... | Read more »
Qube Kingdom Review
Qube Kingdom Review By Nadia Oxford on August 29th, 2014 Our Rating: :: KIND OF A SQUARE KINGDOMUniversal App - Designed for iPhone and iPad Qube Kingdom has cute visuals, but it’s a pretty basic tower defense game at heart.   | Read more »
Fire in the Hole Review
Fire in the Hole Review By Rob Thomas on August 29th, 2014 Our Rating: :: WALK THE PLANKUniversal App - Designed for iPhone and iPad Seafoam’s Fire in the Hole looks like a bright, 8-bit throwback, but there’s not enough booty to... | Read more »
Alien Creeps TD is Now Available Worldwi...
Alien Creeps TD is Now Available Worldwide Posted by Ellis Spice on August 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Dodo Master Review
Dodo Master Review By Jordan Minor on August 29th, 2014 Our Rating: :: NEST EGGiPad Only App - Designed for the iPad Dodo Master is tough but fair, and that’s what makes it a joy to play.   | Read more »
Motorsport Manager Review
Motorsport Manager Review By Lee Hamlet on August 29th, 2014 Our Rating: :: MARVELOUS MANAGEMENTUniversal App - Designed for iPhone and iPad Despite its depth and sense of tactical freedom, Motorsport Manager is one of the most... | Read more »
Motorsport Manager – Beginner Tips, Tric...
The world of Motorsport management can be an unforgiving and merciless one, so to help with some of the stress that comes with running a successful race team, here are a few hints and tips to leave your opponents in the dust. | Read more »
CalPal Update Brings the App to 2.0, Add...
CalPal Update Brings the App to 2.0, Adds Lots of New Stuff Posted by Ellis Spice on August 29th, 2014 [ permalink ] | Read more »

Price Scanner via MacPrices.net

Save up to $300 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
The Rise of Phablets
Carlisle & Gallagher Consulting Group, a businesses and technology consulting firm focused solely on the financial services industry, has released an infographic depicting the convergence of... Read more
Eddy – Cloud Music Player for iPhone/iPad Fre...
Ukraine based CapableBits announces the release of Eddy, its tiny, but smart and powerful cloud music player for iPhone and iPad that allows users to stream or download music directly from cloud... Read more
A&D Medical Launches Its WellnessConnecte...
For consumers and the healthcare providers and loved ones who care for them, A&D Medical, a leader in connected health and biometric measurement devices and services, has launched its... Read more
Anand Lal Shimpi Retires From AnandTech
Anand Lal Shimpi, whose AnandTech Website is famous for its meticulously detailed and thoroughgoing reviews and analysis, is packing it in. Lal Shimpi, who founded the tech site at age 14 in 1997,... Read more
2.5GHz Mac mini, Apple refurbished, in stock...
The Apple Store has Apple Certified Refurbished 2.5GHz Mac minis available for $509, $90 off MSRP. Apple’s one-year warranty is included, and shipping is free. Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Labor Day Weekend MacBook Pro sale; 15-inch m...
B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP. Shipping is free, and B&H charges NY sales tax only. They’ll also include free copies of Parallels Desktop... Read more
Labor Day Weekend iPad mini sale; $50 to $100...
Best Buy has the iPad mini with Retina Display (WiFi models) on sale for $50 off MSRP on their online store for Labor Day Weekend. Choose free shipping or free local store pick up. Price is for... Read more
13-inch 1.4GHz MacBook Air on sale for $899,...
Adorama has the new 2014 13″ 1.4GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY & NJ tax only. Their price is $100 off MSRP. Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.