TweetFollow Us on Twitter

Apr 93 Tips, Tidbits
Volume Number:9
Issue Number:4
Column Tag:Tips & Tidbits

Related Info: Script Manager

Tips & Tidbits

By Neil Ticktin, Editor-in-Chief

This column is your opportunity to spread the word about little bits of information that you find out about. These tidbits can be programming related or they can be user tips that are particularly useful to programmers.

MacTech Magazine will pay $25 for every tip used, and $50 for the Tip of the Month. Or you can take your award in orders or subscriptions.

To submit a tip, send in a letter to the magazine. E-mail is our preferred method, but feel free to send something via the US Mail. See page two for all addresses. If you do send snail mail, enclose a printed copy and a disk copy of the letter so that it does not have to be retyped.

Tip of the month

Here is a simple routine that returns a Boolean indicating whether the monitor is currently set at black & white or color.

/* 1 */

Boolean IsColorOn( void )
 GDHandle hGDevice;
 long   theMode;
 hGDevice = GetMainDevice();
 theMode = (**hGDevice).gdMode;
 theMode &= 0x0000000F;
 if( theMode != 0 ) return( true );
 else return( false );

I figured out how to write this piece of code after struggling with the concept for many months. It’s not a very complex routine, but I searched through every source I had available and never found anything that explained how to do it. I hope this will help others having the same problem.

- Marc White, Corinth, Mississippi

Script Manager Pitfall

If you plan to work with non-Roman script (such as Kanji, Arabic, Hebrew, etc ), there is a subtle - but important - point that Inside Macintosh will not tell you.

Script Manager functions can return wrong answers if the appropriate font is not set in the current GrafPort.

For example, there is a Script Manager function called CharByte which tells you if a given character is part of a two-byte script (or not). After reading the description of CharByte in Inside Macintosh, you will conclude it will know the right answer simply by looking at a piece of text. Wrong!

Unless the current font is a Kanji font, CharByte has no way of knowing that a given character is part of a double-byte Kanji character or whether it is a single-byte Roman character.

The reason is all 256 byte values are “valid” for all Roman fonts. If the current font is, say, Geneva, CharByte will think that 1/2 of a Kanji byte is really a single Roman character.

This is neither clear in Inside Macintosh Vol 5 nor the World Script section in Vol 6, but it is a fairly major point!

- Gar, DataPak Software

Apple’s Lame Disk Cache

After seeing significant I/O performance problems with large disk caches (set via the Memory control panel) I decided to run some benchmarks. I wrote a little application that would write a 400K file to a hard disk in 8K sector aligned chunks with various disk cache sizes and return to me the number of ticks that it took. Here are the results:

400K write

disk cache size 8K at a time

32K 50 ticks

64K 50 ticks

96K 51 ticks

128K 50 ticks

192K 50 ticks

256K 50 ticks

384K 691 ticks

512K 681 ticks

1024K 681 ticks

7680K 678 ticks

It appears that the Apple’s disk cache scheme hits a wall at 384K (in this test, anyway). I linked DTS with these results and got an interesting reply. It turns out that their disk cache scheme is optimized for very small reads and writes - like an application reading one byte at a time from a file without doing it's own buffering. I guess this was a problem back when most people used floppies and small hard drives. But modern apps usually do their own file buffering anyway (read a big piece into a buffer and then take it out of the buffer one byte at a time), so the Apple disk cache scheme becomes more of a hinderance than a help.

Not all reads and writes are cached by the Apple scheme. The formula it uses to decide if any given read or write should be cached is:

/* 2 */

numCacheBlocks = user-defined cache size DIV 512;
maxCachedReadWrite = (numCacheBlocks - 1) * 16;

So, with a cache size of 256K you get:

numCacheBlocks = 512
maxCachedReadWrite = 8176

That means that any read/write larger than 8176 bytes or larger will not be cached. So in my test app, nothing was being cached until the cache was 384K or larger, at which time my 8K writes were being cached (and I got a 13x performance slow-down).

There is hope, though. Page 2-95 of the new Inside Macintosh File Manager documents the "no cache" bit of ioPosMode. You can set bit 5 of ioPosMode to prevent your reads and writes from being cached. I strongly recommend you do this except in those few cases where you know you're going to need the data again right away or where you're not doing your own intelligent sector-aligned buffering. When I set this bit in my test app, my times for writing 400K with very large caches were the same as those for writing 400K with very small caches.

That's great for your code but what about other code that you can't control and that doesn't take advantage of bit 5 of ioPosMode? The only real defense is to reduce your disk cache to the minimum (32K) at which time only very small reads and writes will be cached (1008 bytes or less). But in my own tests with compiling large projects under MPW and Think C I have found that a disk cache size of 128K gives the fastest build times. You should do your own timings based on what type of I/O operations you do most.

- Mike Scanlin

MacTech Regular Contributor

Useless Trivia or a tip?

This is perhaps more fit for “Useless Trivia” than is is for “Tips and Tidbits,” but no matter, here it is:

Nearly every piece of C code that I ever see (even in MacTech Magazine) uses parentheses around all return statements. People always seem to write:

int theirfunc()
  return (1);

Even the examples in K&R itself use parentheses around the return statments. But look at the actual syntax reference in K&R: “if,” “while,” “for,” and “switch” all require parens, but “return” does not. For years, using many compilers, on many machines, I've been writing:

int myfunc()
  return 1;

It may look odd, but try it - it does work!

- Ken Gladstone

MacTech Technical Editor


Community Search:
MacTech Search:

Software Updates via MacUpdate

The best GIF making apps
Animated GIFs have exploded in popularity recently which is likely thanks to a combination of Tumblr, our shorter attention spans, and the simple fact they’re a lot of fun. [Read more] | Read more »
The best remote desktop apps for iOS
We've been sifting through the App Store to find the best ways to do computer tasks on a tablet. That gave us a thought - what if we could just do computer tasks from our tablets? Here's a list of the best remote desktop apps to help you use your... | Read more »
Warhammer 40,000: Freeblade guide - How...
Warhammer 40,000: Freebladejust launched in the App Store and it lets you live your childhood dream of blowing up and slashing a bunch of enemies as a massive, hulking Space Marine. It's not easy being a Space Marine though - and particularly if... | Read more »
Gopogo guide - How to bounce like the be...
Nitrome just launched a new game and, as to be expected, it's a lot of addictive fun. It's called Gopogo, and it challenges you to hoparound a bunch of platforms, avoiding enemies and picking up shiny stuff. It's not easy though - just like the... | Read more »
Sago Mini Superhero (Education)
Sago Mini Superhero 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: KAPOW! Jack the rabbit bursts into the sky as the Sago Mini Superhero! Fly with Jack as he lifts impossible weights,... | Read more »
Star Wars: Galaxy of Heroes guide - How...
Star Wars: Galaxy of Heroes is all about collecting heroes, powering them up, and using them together to defeat your foes. It's pretty straightforward stuff for the most part, but increasing your characters' stats can be a bit confusing because it... | Read more »
The best cooking apps (just in time for...
It’s that time of year again, where you’ll be gathering around the dinner table with your family and a huge feast in front of you. [Read more] | Read more »
Square Rave guide - How to grab those te...
Square Rave is an awesome little music-oriented puzzle game that smacks of games like Lumines, but with its own unique sense of gameplay. To help wrap your head around the game, keep the following tips and tricks in mind. [Read more] | Read more »
Snowboard Party 2 (Games)
Snowboard Party 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Crowned the best snowboarding game available on the market, Snowboard Party is back to fulfill all your adrenaline needs in... | Read more »
One Button Travel (Games)
One Button Travel 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: “To cut a long story short, If you like interactive fiction, just go buy this one.” - “Oozes the polish that... | Read more »

Price Scanner via

Holiday weekend Mac sales roundup: B&H Ph...
B&H Photo continues to have all new Macs on sale for up to $500 off MSRP as part of their Black Friday/Holiday weekend sale. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina... Read more
iMobie Releases its Ace iOS Cleaner PhoneClea...
iMobie Inc. has announced the new update of PhoneClean 4, its iOS cleaner designed to reclaim wasted space on iPhone/iPad for use and keep the device fast. Alongside, iMobie hosts a 3-day giveaway of... Read more
U.S. Cellular Offering iPad Pro
U.S. Cellular today announced that it is offering the new iPad Pro with Wi-Fi + Cellular, featuring a 12.9-inch Retina display with 5.6 million pixels — the most ever in an iOS device. U.S. Cellular... Read more
Newegg Canada Unveils Black Friday Deals for...
Newegg Canada is offering more than 1,000 deep discounts to Canadian customers this Black Friday, available now through Cyber Monday, with new deals posted throughout the week. “Black Friday is... Read more
Black Friday: Macs on sale for up to $500 off...
BLACK FRIDAY B&H Photo has all new Macs on sale for up to $500 off MSRP as part of their early Black Friday sale including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $... Read more
Black Friday: Up to $125 off iPad Air 2s at B...
BLACK FRIDAY Walmart has the 16GB iPad Air 2 WiFi on sale for $100 off MSRP on their online store. Choose free shipping or free local store pickup (if available): - 16GB iPad Air 2 WiFi: $399, save $... Read more
Black Friday: iPad mini 4s on sale for $100 o...
BLACK FRIDAY Best Buy has iPad mini 4s on sale for $100 off MSRP on their online store for Black Friday. Choose free shipping or free local store pickup (if available): - 16GB iPad mini 4 WiFi: $299.... Read more
Black Friday: Apple Watch for up to $100 off...
BLACK FRIDAY Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday. Below is a roundup of the deals being offered by authorized Watch resellers:... Read more
Black Friday: Target offers 6th Generation iP...
BLACK FRIDAY Save $40 to $60 on a 6th generation iPod touch at Target with free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: -... Read more
Black Friday: Walmart and Target offer iPod n...
BLACK FRIDAY Walmart has the 16GB iPod nano (various colors) on sale for $119.20 on their online store for a limited time. That’s $30 off MSRP. Choose free shipping or free local store pickup (if... Read more

Jobs Board

Specialist *Apple* /Mac Desktop - University...
…technical support, expertise and user training for a variety of Apple /Macintosh hardware, software and devices.Researches, analyzes and resolves complex Apple Read more
*Apple* Site Security Manager - Apple (Unite...
# Apple Site Security Manager Job Number: 42975010 Culver City, Califo ia, United States Posted: Oct. 2, 2015 Weekly Hours: 40.00 **Job Summary** The Apple Site Read more
WiSE *Apple* Pay Quality Engineer - Apple (...
# WiSE Apple Pay Quality Engineer Job Number: 44313381 Santa Clara Valley, Califo ia, United States Posted: Nov. 13, 2015 Weekly Hours: 40.00 **Job Summary** Join our Read more
Holiday Retail Associate with *Apple* Knowl...
…and assertive.Someone who can troubleshoot iOS devices (iPhone and iPad) and Apple Mail issues.Someone who can offer solutions.Someone who can work weekends.Someone with Read more
*Apple* Systems Engineer (Mclean, VA and NYC...
Summary:Assist in providing strategic direction and technical leadership within the Apple portfolio, including desktops, laptops, and printing environment. This person Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.