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

Deeper 2.2.1 - Enable hidden features in...
Deeper is a personalization utility for macOS which allows you to enable and disable the hidden functions of the Finder, Dock, QuickTime, Safari, iTunes, login window, Spotlight, and many of Apple's... Read more
Spotify 1.0.59.395. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
FileZilla 3.27.0.1 - Fast and reliable F...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.27.0.1: MSW: Add misssing file to .zip binary package... Read more
Sierra Cache Cleaner 11.0.6 - Clear cach...
Sierra Cache Cleaner is an award-winning general purpose tool for macOS X. SCC makes system maintenance simple with an easy point-and-click interface to many macOS X functions. Novice and expert... Read more
Live Home 3D Pro 3.1.2 - $69.99
Live Home 3D Pro, a successor of Live Interior 3D, is the powerful yet intuitive home design software that lets you build the house of your dreams right on your Mac. It has every feature of Live Home... Read more
Pinegrow 3.04 - Mockup and design webpag...
Pinegrow (was Pinegrow Web Designer) is desktop app that lets you mockup and design webpages faster with multi-page editing, CSS and LESS styling, and smart components for Bootstrap, Foundation,... Read more
DiskCatalogMaker 7.1.2 - Catalog your di...
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 for... Read more
Apple iTunes 12.6.2 - Play Apple Music a...
Apple iTunes lets you organize and stream Apple Music, download and watch video and listen to Podcasts. It can automatically download new music, app, and book purchases across all your devices and... Read more
Transmit 5.0 - Excellent FTP/SFTP client...
Transmit is an excellent FTP (file transfer protocol), SFTP, S3 (Amazon.com file hosting) and iDisk/WebDAV client that allows you to upload, download, and delete files over the internet. With the... Read more
Adobe Lightroom 6.12 - Import, develop,...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more

Latest Forum Discussions

See All

The best deals on the App Store this wee...
There are quite a few truly superb games on sale on the App Store this week. If you haven't played some of these, many of which are true classics, now's the time to jump on the bandwagon. Here are the deals you need to know about. [Read more] | Read more »
Realpolitiks Mobile (Games)
Realpolitiks Mobile 1.0 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0 (iTunes) Description: PLEASE NOTE: The game might not work properly on discontinued 1GB of RAM devices (iPhone 5s, iPhone 6, iPhone 6 Plus, iPad... | Read more »
Layton’s Mystery Journey (Games)
Layton’s Mystery Journey 1.0.0 Device: iOS Universal Category: Games Price: $15.99, Version: 1.0.0 (iTunes) Description: THE MUCH-LOVED LAYTON SERIES IS BACK WITH A 10TH ANNIVERSARY INSTALLMENT! Developed by LEVEL-5, LAYTON’S... | Read more »
Full Throttle Remastered (Games)
Full Throttle Remastered 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Originally released by LucasArts in 1995, Full Throttle is a classic graphic adventure game from industry legend Tim... | Read more »
Stunning shooter Morphite gets a new tra...
Morphite is officially landing on iOS in September. The game looks like the space shooter we've been needing on mobile, and we're going to see if it fits the bill quite shortly. The game's a collaborative effort between Blowfish Studios, We're Five... | Read more »
Layton's Mystery Journey arrives to...
As you might recall, Layton's Mystery Journey is headed to iOS and Android -- tomorrow! To celebrate the impending launch, Level-5's released a new trailer, complete with an adorable hamster. [Read more] | Read more »
Sidewords (Games)
Sidewords 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Grab a cup of coffee and relax with Sidewords. Sidewords is part logic puzzle, part word game, all original. No timers. No... | Read more »
Noodlecake Games' 'Leap On!...
Noodlecake Games is always good for some light-hearted arcade fun, and its latest project, Leap On! could carry on that tradition. It's a bit like high stakes tetherball in a way. Your job is to guide a cute little blob around a series of floating... | Read more »
RuneScape goes mobile later this year
Yes, RuneScape still exists. In fact, it's coming to iOS and Android in just a few short months. Jagex, creators of the hit fantasy MMORPG of yesteryear, is releasing RuneScape Mobile and Old School RuneScape for mobile devices, complete with... | Read more »
Crash of Cars wants you to capture the c...
Crash of Cars is going full on medieval in its latest update, introducing castles and all manner of new cars and skins fresh from the Dark Ages. The update introduces a new castle-themed map (complete with catapults) and a gladiator-style battle... | Read more »

Price Scanner via MacPrices.net

Save or Share
FotoJet Designer, is a simple but powerful new graphic design apps available on both Mac and Windows. With FotoJet Designer’s 900+ templates, thousands of resources, and powerful editing tools you... Read more
Logo Maker Shop iOS App Lets Businesses Get C...
A newly released app is designed to help business owners to get creative with their branding by designing their own logos. With more than 1,000 editable templates, Logo Maker Shop 1.0 provides the... Read more
Sale! New 15-inch MacBook Pros for up to $150...
Amazon has the new 2017 15″ MacBook Pros on sale for up to $150 off MSRP including free shipping: – 15″ 2.8GHz MacBook Pro Space Gray: $2249 $150 off MSRP – 15″ 2.89Hz MacBook Pro Space Gray: $2779 $... Read more
DEVONthink To Go 2.1.7 For iOS Brings Usabili...
DEVONtechnologies has updated DEVONthink To Go, the iOS companion to DEVONthink for Mac, with enhancements and bug fixes. Version 2.1.7 adds an option to clear the Global Inbox and makes the grid... Read more
15-inch 2.2GHz Retina MacBook Pro, Apple refu...
Apple has Certified Refurbished 2015 15″ 2.2GHz Retina MacBook Pros available for $1699. That’s $300 off MSRP, and it’s the lowest price available for a 15″ MacBook Pro. An Apple one-year warranty is... Read more
13-inch 2.3GHz Silver MacBook Pro on sale for...
B&H Photo has the new 2017 13″ 2.3GHz/256GB Silver MacBook Pro (MPXU2LL/A) on sale for $1399 including free shipping plus NY & NJ sales tax only. Their price is $100 off MSRP. Read more
Apple Tackles Distracted Driving With iOS 11...
One of the most important new features coming in iOS 11 is Do Not Disturb while driving, intended to help drivers stay more focused on the road. With Do Not Disturb while driving, your iPhone can... Read more
iMazing Mini for Mac: Free Automatic and Priv...
Geneva, Switzerland-based indie developer DigiDNA has released iMazing Mini, their free macOS utility designed to automatically back up iOS devices over any local Wi-Fi network. The app offers users... Read more
Clearance 2016 13-inch MacBook Airs, Apple re...
Apple dropped prices recently on Certified Refurbished 2016 13″ MacBook Airs, with models now available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
9.7-inch 2017 iPads available for $299, save...
B&H Photo has 2017 9.7″ 32GB WiFi iPads on sale for $30 off MSRP for a limited time. Shipping is free, and pay sales tax in NY & NJ only: – 32GB iPad WiFi: $299, $30 off Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple...
SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Payments Architect - *Apple* Pay - A...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
Frameworks Engineering Manager, *Apple* Wat...
Frameworks Engineering Manager, Apple Watch Job Number: 41632321 Santa Clara Valley, California, United States Posted: Jun. 15, 2017 Weekly Hours: 40.00 Job Summary Read more
Manager, *Apple* Media Products - Apple Inc...
Job Summary The Apple Media Products Discovery, Fraud and Abuse team is responsible for protecting the integrity of Apple services. As a manager of the team, you Read more
*Apple* Watch, Accessories, Engineering Proj...
Job Summary Engineering Project Manager, Apple Watch Accessories. The Accessories group is looking for an Engineering Project Manager (EPM) to lead the design and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.