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

Dropbox 193.4.5594 - Cloud backup and sy...
Dropbox is a file hosting service that provides cloud storage, file synchronization, personal cloud, and client software. It is a modern workspace that allows you to get to all of your files, manage... Read more
Google Chrome 122.0.6261.57 - Modern and...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
Skype 8.113.0.210 - Voice-over-internet...
Skype is a telecommunications app that provides HD video calls, instant messaging, calling to any phone number or landline, and Skype for Business for productive cooperation on the projects. This... Read more
Tor Browser 13.0.10 - Anonymize Web brow...
Using Tor Browser you can protect yourself against tracking, surveillance, and censorship. Tor was originally designed, implemented, and deployed as a third-generation onion-routing project of the U.... Read more
Deeper 3.0.4 - 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
OnyX 4.5.5 - Maintenance and optimizatio...
OnyX is a multifunction utility that you can use to verify the startup disk and the structure of its system files, to run miscellaneous maintenance and cleaning tasks, to configure parameters in the... Read more
Hopper Disassembler 5.14.1 - Binary disa...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more

Latest Forum Discussions

See All

Zenless Zone Zero opens entries for its...
miHoYo, aka HoYoverse, has become such a big name in mobile gaming that it's hard to believe that arguably their flagship title, Genshin Impact, is only three and a half years old. Now, they continue the road to the next title in their world, with... | Read more »
Live, Playdate, Live! – The TouchArcade...
In this week’s episode of The TouchArcade Show we kick things off by talking about all the games I splurged on during the recent Playdate Catalog one-year anniversary sale, including the new Lucas Pope jam Mars After Midnight. We haven’t played any... | Read more »
TouchArcade Game of the Week: ‘Vroomies’
So here’s a thing: Vroomies from developer Alex Taber aka Unordered Games is the Game of the Week! Except… Vroomies came out an entire month ago. It wasn’t on my radar until this week, which is why I included it in our weekly new games round-up, but... | Read more »
SwitchArcade Round-Up: ‘MLB The Show 24’...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for March 15th, 2024. We’re closing out the week with a bunch of new games, with Sony’s baseball franchise MLB The Show up to bat yet again. There are several other interesting games to... | Read more »
Steam Deck Weekly: WWE 2K24 and Summerho...
Welcome to this week’s edition of the Steam Deck Weekly. The busy season has begun with games we’ve been looking forward to playing including Dragon’s Dogma 2, Horizon Forbidden West Complete Edition, and also console exclusives like Rise of the... | Read more »
Steam Spring Sale 2024 – The 10 Best Ste...
The Steam Spring Sale 2024 began last night, and while it isn’t as big of a deal as say the Steam Winter Sale, you may as well take advantage of it to save money on some games you were planning to buy. I obviously recommend checking out your own... | Read more »
New ‘SaGa Emerald Beyond’ Gameplay Showc...
Last month, Square Enix posted a Let’s Play video featuring SaGa Localization Director Neil Broadley who showcased the worlds, companions, and more from the upcoming and highly-anticipated RPG SaGa Emerald Beyond. | Read more »
Choose Your Side in the Latest ‘Marvel S...
Last month, Marvel Snap (Free) held its very first “imbalance" event in honor of Valentine’s Day. For a limited time, certain well-known couples were given special boosts when conditions were right. It must have gone over well, because we’ve got a... | Read more »
Warframe welcomes the arrival of a new s...
As a Warframe player one of the best things about it launching on iOS, despite it being arguably the best way to play the game if you have a controller, is that I can now be paid to talk about it. To whit, we are gearing up to receive the first... | Read more »
Apple Arcade Weekly Round-Up: Updates an...
Following the new releases earlier in the month and April 2024’s games being revealed by Apple, this week has seen some notable game updates and events go live for Apple Arcade. What The Golf? has an April Fool’s Day celebration event going live “... | Read more »

Price Scanner via MacPrices.net

Apple Education is offering $100 discounts on...
If you’re a student, teacher, or staff member at any educational institution, you can use your .edu email address when ordering at Apple Education to take $100 off the price of a new M3 MacBook Air.... Read more
Apple Watch Ultra 2 with Blood Oxygen feature...
Best Buy is offering Apple Watch Ultra 2 models for $50 off MSRP on their online store this week. Sale prices available for online orders only, in-store prices may vary. Order online, and choose... Read more
New promo at Sams Club: Apple HomePods for $2...
Sams Club has Apple HomePods on sale for $259 through March 31, 2024. Their price is $40 off Apple’s MSRP, and both Space Gray and White colors are available. Sale price is for online orders only, in... Read more
Get Apple’s 2nd generation Apple Pencil for $...
Apple’s Pencil (2nd generation) works with the 12″ iPad Pro (3rd, 4th, 5th, and 6th generation), 11″ iPad Pro (1st, 2nd, 3rd, and 4th generation), iPad Air (4th and 5th generation), and iPad mini (... Read more
10th generation Apple iPads on sale for $100...
Best Buy has Apple’s 10th-generation WiFi iPads back on sale for $100 off MSRP on their online store, starting at only $349. With the discount, Best Buy’s prices are the lowest currently available... Read more
iPad Airs on sale again starting at $449 on B...
Best Buy has 10.9″ M1 WiFi iPad Airs on record-low sale prices again for $150 off Apple’s MSRP, starting at $449. Sale prices for online orders only, in-store price may vary. Order online, and choose... Read more
Best Buy is blowing out clearance 13-inch M1...
Best Buy is blowing out clearance Apple 13″ M1 MacBook Airs this weekend for only $649.99, or $350 off Apple’s original MSRP. Sale prices for online orders only, in-store prices may vary. Order... Read more
Low price alert! You can now get a 13-inch M1...
Walmart has, for the first time, begun offering new Apple MacBooks for sale on their online store, albeit clearance previous-generation models. They now have the 13″ M1 MacBook Air (8GB RAM, 256GB... Read more
Best Apple MacBook deal this weekend: Get the...
Apple has 13″ M2 MacBook Airs available for only $849 today in their Certified Refurbished store. These are the cheapest M2-powered MacBooks for sale at Apple. Apple’s one-year warranty is included,... Read more
New 15-inch M3 MacBook Air (Midnight) on sale...
Amazon has the new 15″ M3 MacBook Air (8GB RAM/256GB SSD/Midnight) in stock and on sale today for $1249.99 including free shipping. Their price is $50 off MSRP, and it’s the lowest price currently... Read more

Jobs Board

Early Preschool Teacher - Glenda Drive/ *Appl...
Early Preschool Teacher - Glenda Drive/ Apple ValleyTeacher Share by Email Share on LinkedIn Share on Twitter Read more
Senior Software Engineer - *Apple* Fundamen...
…center of Microsoft's efforts to empower our users to do more. The Apple Fundamentals team focused on defining and improving the end-to-end developer experience in Read more
Relationship Banker *Apple* Valley Main - W...
…Alcohol Policy to learn more. **Company:** WELLS FARGO BANK **Req Number:** R-350696 **Updated:** Mon Mar 11 00:00:00 UTC 2024 **Location:** APPLE VALLEY,California Read more
Medical Assistant - Surgical Oncology- *Apple...
Medical Assistant - Surgical Oncology- Apple Hill WellSpan Medical Group, York, PA | Nursing | Nursing Support | FTE: 1 | Regular | Tracking Code: 200555 Apply Now Read more
Early Preschool Teacher - Glenda Drive/ *Appl...
Early Preschool Teacher - Glenda Drive/ Apple ValleyTeacher Share by Email Share on LinkedIn Share on Twitter Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.