TweetFollow Us on Twitter

Mar 95 Dialog Box
Volume Number:11
Issue Number:3
Column Tag:Dialog Box

Dialog Box

By Scott T Boyd, Editor

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Challenging Challenge Challenged

One of the Huffman challenge entrants, Allen Stenger, found a bug in Bob Boonstra’s winning published Huffman code. It’s minor (ushort should be ulong) but it’s a real bug. Fixing it doesn’t change Bob’s speed. Here’s some background on the problem.

- Mike Scanlin
progchallenge@xplain.com

Allen writes:

Subj: Huffman solution error?

I believe I’ve found an error in Bob Boonstra’s published solution to the Huffman challenge (MacTech, January 1995 issue). Look at p. 72, the definition of macro ProcessBitSlow. Observe that temp is declared as register ushort; contrast this with the immediately preceding macros ProcessBit and ProcessBitFast, where it is defined as register ulong. Actually all three should be ulong. The reason is that temp is the offset to the child node; since the node table could be as large as 256K bytes (64K nodes), temp can hold the offset in units of nodes but when ProcessBitSlow does the multiplication temp *= sizeof(DecodeNode), temp may overflow.

I was able to provoke this failure using the following example: The decoded numbers are either 3-bit numbers 0-7 or 16 bits numbers 8000-FFFF. The 3-bit numbers are encoded in 4 bits as 0-7 (i.e., a leading 0 bit followed by the number). The 16 bit numbers are encoded as themselves (they already have a leading 1 bit). Under this scheme A000 is decoded incorrectly.

- Allen Stenger.

Bob replies:

Allen Stenger is correct in pointing out an error in the published solution for the HuffmanDecode challenge. As Allen points out, the declaration of the variable temp in macro ProcessBitSlow should be register ulong.

The bug shows up when both of the following are true: (1) the private storage available exceeds 64K, AND (2) numSymElems is large, greater than ~8K to ~32K, depending on maxMemoryUsage.

The bug does not occur if maxMemoryUsage is <=64K. Condition (2) for the bug is really when the size of the decode table exceeds the available storage. Since each node in the decode table is 4 bytes, and since there are (roughly) 2 nodes in the decode table for each element of the symbol table, the bug shows up under the following conditions:

numSymElems  maxMemoryUsage
> ~8K      > 64K
>~16K           >128K
>~32K           >256K (beyond Challenge limits)
max (2**16-1)   >512K (beyond Challenge limits)

(The relationship to numSymElems is approximate because it depends on the degree of balance in the tree representing the Huffman encoding.)

In these cases, some symbols will be decoded incorrectly. In the case cited by Allen, numSymElems is >32K, and the error shows up if maxMemoryUsage is >64K.

Correcting the bug changes a few xxx.W instructions to xxx.L, but shortens the code generated by the macro in question by one instruction, and actually improves the run time by an almost imperceptible amount.

It just goes to show you can’t do enough testing. My testing used Huffman encodings that were generated from large text files, so I got encodings with a few thousand elements. Still, I should have caught this one by inspection. Congratulations to Allen for detecting the error, and good luck to him in future Challenges.

- Bob Boonstra

Anonymously Yours

I’ve heard that it’s possible to anonymously send e-mail to someone. I’ve also heard that in order for this to be really anonymous you need to send it through three or four anonymous re-mailers. Could you publish the addresses of these remailers and give an example of how to send e-mail that has a very high chance of remaining anonymous?

[name and address withheld]

Great Prograph Coverage

Your January ’95 issue looks like one of the best ever. Two CD-ROMs, who could ask for more? I was also very excited to see Kurt Schmucker’s article on Prograph Commands. I hope that these articles on Prograph become a regular feature. As a former member of the Software Frameworks Association, I’m glad to see MacTech really taking up the slack where Frameworks left off. I have been working with Prograph CPX for several months now and find it to be a great tool.

Please keep up your coverage of it, and other new OOP technologies.

- Steve Wilson , Emergent Behavior
emergent@aol.com

Do the Cobbler’s Children Always Go Barefoot?

I am inspired to write after reading the letter by Steve Weller, "A Trail of Good Intentions", printed in the December Dialog Box. Like Steve, I always thought that "C" stood for cryptic but C++ is much worse.

I can best describe myself as a classic Mac hacker, that is one who programs the Mac for the sheer joy of it and not

to make a living. As a programmer, my user interface is the editor I use. I have made a few dollars on shareware but mostly I program the Mac just because I love the Mac’s user interface.

You can judge the low quality of the editors that come with most C++ compilers by the number of third party editors being sold. I personally can’t stand to use any of the popular C++ environments (with or without third party editors) because they don’t just compare to the editor in THINK Pascal.

THINK Pascal’s editor automatically formats my source code. It finds syntax errors before I waste time trying to compile. Most of the Mac user interface is in the Runtime and Interface libraries so I seldom have to include other libraries or interfaces. The stops are easier and quicker to use than the ones in C++. Best of all, the compiler and linker are very fast for reasonable sized programs.

The only thing I have found that really slows THINK Pascal is when I play with MacApp, TCL or one of the other bloated object libraries. For my serious programs I use THINK Pascal with a non-object shell generated by Marksman. In spite of the fact that THINK Pascal hasn’t been updated for several years, I am still more productive using it than C++.

I wish the technical support engineers who write the Symantec Top Ten would answer these two questions.

#1 When is Symantec going to produce a new version of THINK Pascal that will generate both 680x0 and PowerPC code?

#2 Why don’t they transplant the advanced editor, compiler and linker technologies found in THINK Pascal to their slow user hostile C++?

- Fred Johnson
70651.3171@compuserve.com

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Firefox 37.0 - Fast, safe Web browser. (...
Firefox 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 and casual... Read more
Arq 4.11 - Online backup to Google Drive...
Arq is super-easy online backup for the Mac. Back up to your own Google Drive storage (15GB free storage), your own Amazon Glacier ($.01/GB per month storage) or S3, or any SFTP server. Arq backs up... Read more
MacFamilyTree 7.3.4 - Create and explore...
MacFamilyTree gives genealogy a facelift: it's modern, interactive, incredibly fast, and easy to use. We're convinced that generations of chroniclers would have loved to trade in their genealogy... Read more
Yummy FTP 1.10.2 - FTP/SFTP/FTPS client...
Yummy FTP is an FTP + SFTP + FTPS file transfer client which focuses on speed, reliability and productivity. Whether you need to transfer a few files or a few thousand, schedule automatic backups, or... Read more
VueScan 9.5.08 - 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
Iridient Developer 3.0.1 - Powerful imag...
Iridient Developer (was RAW Developer) is a powerful image conversion application designed specifically for OS X. Iridient Developer gives advanced photographers total control over every aspect of... Read more
Air Video Server HD 2.1.0 - Stream video...
Air Video Server HD streams videos instantly from your computer on your iPhone, iPad, iPod touch or Apple TV. No need to worry about converting or transferring files. We took everything that was... Read more
Duplicate Annihilator 5.7.5 - Find and d...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator... Read more
BusyContacts 1.0.2 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
Capture One Pro 8.2.0.82 - RAW workflow...
Capture One Pro 8 is a professional RAW converter offering you ultimate image quality with accurate colors and incredible detail from more than 300 high-end cameras -- straight out of the box. It... Read more

2K Announces WWE 2K, Mobile's First...
It seems like this month has been pretty big for wrestling. First Wrestlemania, then 2K has announces that they're releasing  WWE 2K for iOS. It's a simulation-based WWE game where you'll get to play with several WWE superstars such as John Cena, ... | Read more »
How the Apple Watch Could Change the Fac...
The Apple Watch is still a ways out, but my previous musings on the wearable’s various features got me thinking: what might it be like a year after launch? Two years? Five years? What if it becomes a symbiotic part of the iOS framework to the point... | Read more »
Pie In The Sky: A Pizza Odyssey (Games)
Pie In The Sky: A Pizza Odyssey 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: A game about delivering pizza. In space. | Read more »
Chosen Gives Hopeful Singers, Songwriter...
If YouTube videos and reality TV shows like The Voice have taught us one thing, it’s that there are a lot of people out there who are anxious to show the world their talents. And if they’ve taught us a second thing, it’s that there’s an almost... | Read more »
Android's Popular OfficeSuite Now A...
Once only available for Android devices, OfficeSuite has finally landed on the app store. The Mobile Systems app lets you view, edit, create, and share Word, Excel, and PowerPoint documents as well as convert them to/from PDFs. It's touted as being... | Read more »
Warhammer: Arcane Magic is Coming Soon,...
Turbo Tape Games has announced that they're joining forces with Games Workshop to bring the turn-based strategy board game, Warhammer: Arcane Magic, to life on the iOS. | Read more »
Fast & Furious: Legacy's Creati...
| Read more »
N-Fusion and 505's Ember is Totally...
| Read more »
These are All the Apple Watch Apps and G...
The Apple Watch is less than a month from hitting store shelves, and once you get your hands on it you're probably going to want some apps and games to install. Fear not! We've compiled a list of all the Apple Watch apps and games we've been able to... | Read more »
Appy to Have Known You - Lee Hamlet Look...
Being at 148Apps these past 2 years has been an awesome experience that has taught me a great deal, and working with such a great team has been a privilege. Thank you to Rob Rich, and to both Rob LeFebvre and Jeff Scott before him, for helping me... | Read more »

Price Scanner via MacPrices.net

Adobe Brings Powerful Layout-Design Capabilit...
Adobe today announced the availability of Adobe Comp CC, a free iPad app that enables rapid creation of layout concepts for mobile, Web and print projects. With Comp CC, designers can rough out and... Read more
Apple offering refurbished 27-inch 5K iMacs f...
The Apple Store is offering Apple Certified Refurbished 27″ 3.5GHz 5K iMacs for $2119 including free shipping. Their price is $380 off the price of new models, and it’s the lowest price available for... Read more
16GB iPad mini on sale for $199, save $50
Walmart has 16GB iPad minis (1st generation) available for $199.99 on their online store, including free shipping. Their price is $50 off MSRP. Online orders only. Read more
New 128GB MacBook Airs on sale for $50 off MS...
 B&H Photo has 128GB 11″ and 13″ 2015 MacBook Airs on sale today for $50 off MSRP including free shipping plus NY sales tax only: - 11″ 1.6GHz/128GB MacBook Air (Model #MJVM2LL/A): $849 $50 off... Read more
13-inch 2.6GHz Retina MacBook Pro (refurbishe...
The Apple Store has Apple Certified Refurbished 13″ 2.6GHz/128GB Retina MacBook Pros available for $979 including free shipping. Original MSRP for this model was $1299. Read more
Save up to $600 with Apple refurbished Mac Pr...
The Apple Store is offering Apple Certified Refurbished Mac Pros for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Samsung Galaxy S 6 and Galaxy S 6 edge U.S. P...
Samsung Electronics America, Inc. has announced the Galaxy S 6 and Galaxy S 6 edge will be available in the U.S. beginning April 10, with pre-orders being accepted now. “We have completely reimagined... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.... Read more
Save up to $80 on iPad Air 2s, NY tax only, f...
 B&H Photo has iPad Air 2s on sale for $80 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469.99 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
iMacs on sale for up to $205 off MSRP
B&H Photo has 21″ and 27″ iMacs on sale for up to $205 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $1019 $80 off - 21″ 2.7GHz iMac: $1189 $110 off - 21″ 2.9GHz... Read more

Jobs Board

DevOps Software Engineer - *Apple* Pay, iOS...
**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
*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
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional 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
*Apple* Pay - Site Reliability Engineer - Ap...
**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.