TweetFollow Us on Twitter

May 96 Tips
Volume Number:12
Issue Number:5
Column Tag:Tips & Tidbits

Tips & Tidbits

By Steve Sisak

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

Invoking Handlers in Scripts, by Name

This is completely undocumented, as far as I know, but it may help. Suppose you have a script application containing a function:

on DoSomething(param1,param2)
 return param1+param2
end DoSomething

From C, you just have to send the script application an Apple event like this one:

CLASS: ascr

type: psbr

direct object: "----" "LIST"

(the list of AEDescs of parameters to pass to the script function)

additional parameter: "snam" "TEXT"

containing the name of the function to call (in our example: “DoSomething”)

et voilà.

This method allows to write “clean” scripts, using more memorable handler names, not using the «CLASStype» syntax.

Pierre-Loic Raynaud

[This event is called “Subroutine Call” and is described in more detail in Chapter 10 of the Apple Event Registry, “The AppleScript Suite”. On the Developer Mailing Reference Library CD, the pdf file is named “AppleScript Suite”, and the information is on pdf page 5 (paper page 7). - jk]

Swapping Bytes in a High Level Language,
the Saga Continues!

You have probably been swamped with everyone’s comments regarding the “Anti-Tip of the Month” that appeared in MacTech Magazine 11.10 (October 1995).

Greg Poole had the right idea when he submitted his tip about byte-swapping. You can tweak code until your fingers fall off, but often the best way to make something faster is by finding a better way of doing the same thing.

I have attached two files to this message: ByteSwap.c & ByteSwap.h. In a nutshell, we do our swapping as follows:

ByteSwap.h
#define SwapShort(myUnsignedShort)  \
 ((myUnsignedShort)>>8)|((myUnsignedShort)<<8)

In use:

{
    unsigned short someValue = 0x3210;
    someValue = SwapShort(someValue);
}

We quite simply move the hi-byte right, and the lo-byte left, then OR them back together.


ByteSwap.c
#include "byteswap.h"

unsigned long TransposeLong(unsigned long value)
{
  unsigned long   returnValue;
  ((unsigned char *) &returnValue)[3] = 
 ((unsigned char *) &value)[0];
  ((unsigned char *) &returnValue)[2] = 
 ((unsigned char *) &value)[1];
  ((unsigned char *) &returnValue)[1] = 
 ((unsigned char *) &value)[2];
  ((unsigned char *) &returnValue)[0] = 
 ((unsigned char *) &value)[3];
  return returnValue;
}

David Most

The Technical Editor Responds

There are quite a few methods available for byte swapping, but which algorithm is the best depends a great deal on the compiler and processor you are using. For instance, the PowerPC (and many other processors) have instructions specifically for this purpose. Unfortunately, since the C and C++ languages have not kept up with current processors (C is basically processor-independent PDP-11 assembly language), it is our job to trick the compiler into generating the correct code.

Some compilers provide directives for this purpose. For instance, if you are using CodeWarrior on a PowerPC you can just say:

inline long SwapLong(long val)
{
    return __XXXXX(val);  //  <<<need intrinsic for load byte-swapped>>>
}

You may notice that I’m using C++ inline functions here instead of C #defines. To quote the “Apple Unofficial C++ Style Guide” (develop 2, p. 209): “One of the most powerful features of the C++ language is the C preprocessor. Don’t use it.” Inline functions are not only more readable than preprocessor macros, but, because they limit side effects, allow the compiler more latitude in optimizing your code.

Barring that, we need to find something that we can say in C that can get bytes swapped without generating egregiously bad code. David’s solution is probably a good one for shorts because it is a pure mathematical expression, allowing the compiler to optimize it in any way it chooses. For longs, his solution is one of the safest, if you know nothing about the compiler and/or processor you’re building for. (I would, however, convert both to inline functions.)

However, if you do know something about your processor, you can do better. In the case of the PPC, you really want to get your compiler to emit a load byte-swapped instruction. On a 680x0, you have a little latitude. One trick that comes to mind is that the 680x0 has predecrement and postincrement addressing modes. This means that:

foo = *p++ and foo = *--p

are fast and (1 instruction)

foo = *++p and foo = *p--

are slow (3 instructions). Therefore we can swap a long on a 680x0 with:

inline long SwapLong(long val)
{
    Byte* p = ((Byte*) val)[4];  // 680x0’s are big-endian

 long val = *--p;
 val  = (val << 8) | *--p;
 val  = (val << 8) | *--p;
  return (val << 8) | *--p;
}

The PowerPC has only post-increment instructions, so this will generate lousy code. (If someone would like to time a bunch of approaches, I’d be glad to publish the results.)

I must say that the bottom line is: this is all a bunch of work that would be completely unnecessary if the C language had kept up with reality. Here’s my proposal to the ANSI committee:

Make littleendian and bigendian storage classifiers like const and volatile. Then I could just type:

typedef struct Foo
{
    littleendian long    bar;
    bigendian short      baz;
} Foo;

void blah(Foo* foo)
{
    long  bar = foo->bar;
    short baz = foo->baz;

    ...
}

...and let the compiler deal with it while I spend my time writing code which does real work.

- sgs

Fix For Tip Of The Month, January 1996

I’m sending this short note just to point out that, although Greg Poole is right in writing that a file or directory can be moved by the CatMove function only if both the source and destination are on the same volume, he seems to forget that every Macintosh volume, not just the System volume, has a Trash folder.

Thus, if we pass to the FindFolder function the volume reference number of the file to be deleted instead of the constant kOnSystemDisk, we will be able to find the directory ID of the local Trash.

Line #44 of “FSpTrashFile.c” source file should be changed from:

theErr = FindFolder( kOnSystemDisk, kTrashFolderType, 
  kDontCreateFolder, &vRefNum, &dirID );

to:

theErr = FindFolder( (*theFile).vRefNum, kTrashFolderType, 
  kDontCreateFolder, &vRefNum, &dirID );

Live Long and Prosper!

Luigi Belverato

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Google Chrome 63.0.3239.108 - 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
Paparazzi! 1.0b7 - Make user-defined siz...
Paparazzi! is a small utility for OS X that makes screenshots of webpages. This very simple tool takes screenshots of websites which do not fit on one screen. You specify the desired width, minimal... Read more
Remotix 5.0.4 - Access all your computer...
Remotix is a fast and powerful application to easily access multiple Macs (and PCs) from your own Mac. Features Complete Apple Screen Sharing support - including Mac OS X login, clipboard... Read more
Apple Configurator 2.6 - Configure and d...
Apple Configurator makes it easy to deploy iPad, iPhone, iPod touch, and Apple TV devices in your school or business. Use Apple Configurator to quickly configure large numbers of devices connected to... Read more
Amadeus Pro 2.4.4 - Multitrack sound rec...
Amadeus Pro lets you use your Mac for any audio-related task, such as live audio recording, digitizing tapes and records, converting between a variety of sound formats, etc. Thanks to its outstanding... Read more
Mellel 4.0.3 - The word processor for sc...
Mellel is the leading word processor for OS X and has been widely considered the industry standard for long form documents since its inception. Mellel focuses on writers and scholars for technical... Read more
Suitcase Fusion 8 19.0.3 - Font manageme...
Suitcase Fusion 8 is the creative professional's font manager. Every professional font manager should deliver the basics: spectacular previews, powerful search tools, and efficient font organization... Read more
Final Cut Pro X 10.4 - Professional vide...
Final Cut Pro X is a professional video editing solution. Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Compressor 4.4 - Adds power and flexibil...
Compressor adds power and flexibility to Final Cut Pro X export. Customize output settings, work faster with distributed encoding, and tap into a comprehensive set of delivery features. Features... Read more
Cocktail 11.2 - General maintenance and...
Cocktail is a general purpose utility for macOS that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more

Latest Forum Discussions

See All

Match blocks to pull off dance moves in...
Ferdinand: Unstoppabull is a brand new match three puzzler based on the animated movie of (almost) the same name. As you can expect, you have to match blocks together to complete a bunch of puzzling levels and earn a high score. [Read more] | Read more »
Lineage 2: Revolution’s end of year upda...
Now available in 54 countries worldwide, Lineage 2: Revolution is continuing its global quest to be the most popular mobile MMORPG by launching a jam-packed end of year update. Complete with many subtle tweaks to help improve users’ online... | Read more »
The 5 best Star Wars games on iOS
The time has almost come.Star Wars: The Last Jedifinally hits theaters in the cinematic event that might be bigger than Christmas. To celebrate, we're taking a look at the best--and only the best--Star Warsmobile games to date. [Read more] | Read more »
Life Is Strange (Games)
Life Is Strange 1.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1 (iTunes) Description: Life Is Strange is a five part episodic game that sets out to revolutionize story-based choice and consequence games by... | Read more »
Oddworld: New 'n' Tasty (Game...
Oddworld: New 'n' Tasty 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: ** PLEASE NOTE: Requires 3.6GB free space to install. Runs at variable resolutions based on device capabilities.... | Read more »
Gorogoa (Games)
Gorogoa 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Gorogoa is an elegant evolution of the puzzle genre, told through a beautifully hand-drawn story designed and illustrated by Jason... | Read more »
Why Guns of Boom will be big for mobile...
Earlier this week, Game Insight, the minds that brought you Guns of Boom, revealed plans for an esports mode in the popular FPS title, with big implications for the game's future. Guns of Boom has been quite popular for some time now, so it's... | Read more »
The best mobile games to play on lazy ho...
With the holidays in full swing, there's hopefully going to be a lot of time off work lazing around the house. With all of that free time, it's a perfect opportunity to catch up on some mobile games that you might have missed out on earlier this... | Read more »
Rules of Survival guide - how to boost y...
It's not easy surviving in the "every-man-for-himself" world of Rules of Survival. You'll be facing off against many other players who might be more skilled than you, or are luckier than you. There are a lot of factors weighing against you. With... | Read more »
FEZ Pocket Edition (Games)
FEZ Pocket Edition 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Updated Price Trackers: Macs, iPads, iPhones,...
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: – 15″... Read more
How to preorder a new iMac Pro and pay zero s...
B&H Photo and Adorama are accepting preorders on multiple configurations of the new Apple iMac Pro. Both resellers charge sales tax for residents of NY & NJ only, and shipping is free.... Read more
Apple Macs back in stock at Amazon with model...
Amazon has MacBook Pros, MacBook Airs, MacBooks, and iMacs on sale for up to $200 off MSRP as part of their Holiday/Christmas sale. Shipping is free. Note that stock of some Macs may come and go (and... Read more
Apple offering free overnight delivery on all...
Apple is now offering free overnight delivery on all in stock products until 3pm local time on December 22nd. This includes new as well as refurbished computers. Click here for more information. Read more
Beats Holiday sale at B&H, headphones and...
B&H Photo has Beats by Dr. Dre headphones, earphones, and speakers on sale for up to $80 off MSRP as part of their Holiday sale. Expedited shipping is free, and B&H charges sales tax to NY... Read more
Holiday sale: Apple resellers offer 2017 15″...
MacMall has 15″ MacBook Pros on sale for $220-$300 off MSRP, each including free shipping: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2179, $220 off MSRP – 15″ 2.8GHz MacBook Pro Silver (... Read more
Holiday sale: Apple resellers offer 13″ MacBo...
B&H Photo has 13″ MacBook Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 13-inch 2.3GHz/128GB Space Gray MacBook Pro (... Read more
Apple Watch Series 2, Certified Refurbished,...
Apple has Certified Refurbished Apple Watch Nike+ Series 2s, 42mm Space Gray Aluminum Case with Anthracite/Black Nike Sport Bands, available for $249 (38mm) or $279 (42mm). The 38mm model was out of... Read more
Apple offers Certified Refurbished 2016 12″ R...
Apple has Certified Refurbished 2016 12″ Retina MacBooks available starting at $949. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The following... Read more
B&H drops price on 13″ 256GB MacBook Air...
B&H has the 13″ 1.8GHz/256GB Apple MacBook Air (MQD42LL/A) now on sale for $1079 including free shipping plus NY & NJ sales tax only. Their price is $120 off MSRP, and it’s the lowest price... 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* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform 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
Payments Counsel, *Apple* Pay (payments, cr...
# Payments Counsel, Apple Pay (payments, credit/debit) Job Number: 112941729 Santa Clara Valley, California, United States Posted: 13-Dec-2017 Weekly Hours: 40.00 Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 113124408 Waterford, CT, Connecticut, United States Posted: 17-Oct-2017 Weekly Hours: 40.00 **Job Summary** Are you Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.