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

Apple Security Update 2016-003 Supplemen...
Apple Security Update is recommended for all users and improves the security of OS X. For detailed information about the security content of this update, please visit: http://support.apple.com/kb/... Read more
Apple macOS Sierra 10.12.3 - The latest...
With Apple macOS Sierra, Siri makes its debut on Mac, with new features designed just for the desktop. Your Mac works with iCloud and your Apple devices in smart new ways, and intelligent... Read more
BetterTouchTool 1.992 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
Viber 6.5.5 - 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, so... Read more
Opera 42.0.2393.137 - High-performance W...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
iClock Pro 3.4.7 - Customize your menuba...
iClock Pro is a menu bar replacement clock for Apple's default clock. iClock Pro is an update, total rewrite and improvement to the popular iClock. Have the day, date and time in different fonts and... Read more
PhotoDesk 4.1.5 - Instagram client for p...
PhotoDesk lets you view, like, comment, and download Instagram pictures/videos. (NO Uploads! / Image Posting! Instagram forbids that! AND you need an existing Instagram account). But you can do so... Read more
Capo 3.5.1 - Slow down and learn to play...
Capo lets you slow down your favorite songs so you can hear the notes and learn how they are played. With Capo, you can quickly tab out your songs atop a highly-detailed OpenCL-powered spectrogram... Read more
HandBrake 1.0.2 - Versatile video encode...
HandBrake is a tool for converting video from nearly any format to a selection of modern, widely supported codecs. Features Supported Sources VIDEO_TS folder, DVD image or real DVD (unencrypted... Read more
Sound Studio 4.8.6 - Robust audio record...
Sound Studio lets you easily record and professionally edit audio on your Mac. Easily rip vinyls and digitize cassette tapes, or record lectures and voice memos. Prepare for live shows with live... Read more

Collect pets and sling arrows in Arcane...
Mobile gaming is a crowded market, but regular updates are a good way to keep us attention-short players keen. The brand new content in Arcane Online is a prime example. Published by Japanese developer Gala, Arcane Online is a fantasy MMO that... | Read more »
Super Mario Run dashes onto Android in M...
Super Mario Run was one of the biggest mobile launches in 2016 before it was met with a lukewarm response by many. While the game itself plays a treat, it's pretty hard to swallow the steep price for the full game. With that said, Android users... | Read more »
WarFriends Beginner's Guide: How to...
Chillingo's new game, WarFriends, is finally available world wide, and so far it's a refreshing change from common mobile game trends. The game's a mix of tower defense, third person shooter, and collectible card game. There's a lot to unpack here... | Read more »
Super Gridland (Entertainment)
Super Gridland 1.0 Device: iOS Universal Category: Entertainment Price: $1.99, Version: 1.0 (iTunes) Description: Match. Build. Survive. "exquisitely tuned" - Rock Paper Shotgun No in-app purches, and no ads! | Read more »
Red's Kingdom (Games)
Red's Kingdom 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Mad King Mac has kidnapped your father and stolen your golden nut! Solve puzzles and battle goons as you explore and battle your... | Read more »
Turbo League Guide: How to tame the cont...
| Read more »
Fire Emblem: Heroes coming to Google Pla...
Nintendo gave us our first look at Fire Emblem: Heroes, the upcoming mobile Fire Emblem game the company hinted at last year. Revealed at the Fire Emblem Direct event held today, the game will condense the series' tactical RPG combat into bite-... | Read more »
ReSlice (Music)
ReSlice 1.0 Device: iOS Universal Category: Music Price: $9.99, Version: 1.0 (iTunes) Description: Audio Slice Machine Slice your audio samples with ReSlice and create flexible musical atoms which can be triggered by MIDI notes or... | Read more »
Stickman Surfer rides in with the tide t...
Stickson is back and this time he's taken up yet another extreme sport - surfing. Stickman Surfer is out this Thursday on both iOS and Android, so if you've been following the other Stickman adventures, you might be interested in picking this one... | Read more »
Z-Exemplar (Games)
Z-Exemplar 1.4 Device: iOS Universal Category: Games Price: $3.99, Version: 1.4 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Roundup of 15-inch Touch Bar MacBook Pro sale...
B&H Photo has the new 2016 15″ Apple Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.7GHz Touch Bar... Read more
Apple refurbished iPad Pros available for up...
Apple has Certified Refurbished 9″ and 12″ Apple iPad Pros available for up to $160 off the cost of new iPads. An Apple one-year warranty is included with each model, and shipping is free: - 32GB 9″... Read more
16GB iPad Air 2, Apple refurbished, available...
Apple has Certified Refurbished 16GB iPad Air 2s available for $319 including free shipping. A standard Apple one-year is included. Their price is $60 off original MSRP for this model. Read more
Apple iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ and 27″ Apple iMacs on sale for up to $120 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2199 $100 off MSRP - 27″ 3.2GHz/1TB Fusion iMac... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more
Save up to $350 with Apple Certified Refurbis...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more
2015 12-inch Retina MacBooks, Apple refurbish...
Apple has Certified Refurbished 2015 12″ Retina MacBooks available for up to $410 off original MSRP. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The... Read more
Apple offering Certified Refurbished Series 1...
Apple is now offering Certified Refurbished Series 1 and Series 2 Apple Watches for 14-16% off MSRP, starting at $229. An Apple one-year warranty is included with each watch. Shipping is free: Series... Read more
12-inch 1.2GHz Space Gray Retina MacBook on s...
Amazon has the 2016 12″ 1.2GHz/512GB Space Gray Retina MacBook (Apple model #MLH82LL/A) on sale for $1299.99 including free shipping. Their price is $300 off MSRP. Read more
Twelve South Releases RelaxedLeather Cases fo...
Inspired by the laid-back luxury of burnished leather boots and crafted in rich tones of taupe, herb and marsala, RelaxedLeather cases deliver smart, easy protection for the iPhone 7. Each genuine... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Site Security Manager - Apple (Unite...
# Apple Site Security Manager Job Number: 54692472 Culver City, California, United States Posted: Jan. 19, 2017 Weekly Hours: 40.00 **Job Summary** The Apple Read more
*Apple* macOS Systems Integration Administra...
…most exceptional support available in the industry. SCI is seeking an Junior Apple macOS systems integration administrator that will be responsible for providing Read more
*Apple* Retail - Multiple Positions- Deer Pa...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.