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

OmniOutliner Pro 4.2 - Pro version of th...
OmniOutliner Pro is a flexible program for creating, collecting, and organizing information. Give your creativity a kick start by using an application that's actually designed to help you think. It's... Read more
VLC Media Player 2.2.1 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Nisus Writer Pro 2.1.1 - Multilingual wo...
Nisus Writer Pro is a powerful multilingual word processor, similar to its entry level products, but brings new features such as table of contents, indexing, bookmarks, widow and orphan control,... Read more
Tinderbox 6.2.0 - Store and organize you...
Tinderbox is a personal content management assistant. It stores your notes, ideas, and plans. It can help you organize and understand them. And Tinderbox helps you share ideas through Web journals... Read more
OmniOutliner 4.2 - Organize your ideas,...
OmniOutliner is a flexible program for creating, collecting, and organizing information. Give your creativity a kick start by using an application that's actually designed to help you think. It's... Read more
Things 2.5.4 - Elegant personal task man...
Things is a task management solution that helps to organize your tasks in an elegant and intuitive way. Things combines powerful features with simplicity through the use of tags and its intelligent... Read more
NeoOffice 2014.10 - Mac-tailored, OpenOf...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
iPhoto Library Manager 4.2 - Manage mult...
iPhoto Library Manager allows you to organize your photos among multiple iPhoto libraries, rather than having to store all of your photos in one giant library. You can browse the photos in all your... Read more
Web Snapper 3.3.8 - Capture entire Web p...
Web Snapper lets you capture Web pages exactly as they appear in your browser. You can send them to a file as images or vector-based, multi-page PDFs. It captures the whole Web page - eliminating the... Read more
TeamViewer 10.0.41404 - Establish remote...
TeamViewer gives you remote control of any computer or Mac over the Internet within seconds, or can be used for online meetings. Find out why more than 200 million users trust TeamViewer! Free for... Read more

Chainsaw Warrior: Lords of the Night has...
It's time to put the Darkness back in its place now that Chainsaw Warrior: Lords of the Night has officially made it to iOS. | Read more »
A World of Ice and Fire Lets You Stalk 2...
George R. R. Martin’s A World of Ice and Fire, by Random House, is a mobile guide to the epic series. The new update gives you the Journeys map feture that will let you track the movements of 25 different characters. But don't worry, you can protect... | Read more »
Gameloft Announces Battle Odyssey, a New...
Battle Odyssey, Gameloft's newest puzzle RPG, is coming to the App Store next week. Set in the world of Pondera, you will need to control the power of the elements to defend the world from evil. You'll be able to entlist over 500 allies to aid you... | Read more »
Fusion - HDR Camera (Photography)
Fusion - HDR Camera 1.0.0 Device: iOS Universal Category: Photography Price: $1.99, Version: 1.0.0 (iTunes) Description: Fusion creates HDR (high dynamic range) photos by capturing different exposures and then combining them into one... | Read more »
Sago Mini Toolbox (Education)
Sago Mini Toolbox 1.1 Device: iOS Universal Category: Education Price: $2.99, Version: 1.1 (iTunes) Description: Come build with the Sago Mini friends! Use a wrench, try a saw, or hammer some nails. From sewing hand puppets to... | Read more »
You Should Probably Grab Hitman GO While...
Hitman GO is a surprisingly cool (yet also incredibly drastic) departure from the Hitman series. It's well worth playing for any puzzle game fans out there, and at the moment you can get your hands - or garrotte if you will - on it for a mere $0.99... | Read more »
IFTTT is Bringing Do Button and Do Note...
IFTTT has announced Do Button and Do Note for the Apple Watch. Do Button lets you make your own personalized button that can connect to things like your Google Drive, control the temperature in your home with Nest Thermostat, or turn the lights on... | Read more »
How Many Days, Hours, and Minutes Are Le...
Countdown, by Yves Tscherry, is now available on the App Store. The app keeps track of countdowns to your favorite things such as someones birthday or days till the New Year. You can display the time in seconds, minutes, hours, days, weeks, months,... | Read more »
The All-New Misfit 2.0 App is Available...
Misfit has just given their app a complete overhaul. Misfit 2.0 now has a brand new interface with a sleek design and is easier to navigate. You'll be able to sync your Misfit device and look up health and fitness information faster than ever before... | Read more »
Halo: Spartan Strike (Games)
Halo: Spartan Strike 1.0 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0 (iTunes) Description: Delve into 30 challenging missions through cities and jungles using a devastating arsenal of weapons, abilities and... | Read more »

Price Scanner via MacPrices.net

TigerText Introduces First Secure Enterprise...
TigerText, a provider of secure, real-time messaging for the enterprise, has announced the launch of TigerText for the Apple Watch. TigerText for the Apple Watch enables users to securely send and... Read more
The Conservation Fund Partners with Apple To...
The Conservation Fund has announced that it will partner with Apple to help protect working forests in the United States. The Apple initiative will conserve more than 36,000 acres of working... Read more
Clearance 13-inch 2.6GHz Retina MacBook Pro a...
B&H Photo has clearance 2014 13″ 2.6GHz/128GB Retina MacBook Pros now available for $1099, or $200 off original MSRP. Shipping is free, and B&H charges NY sales tax only. Read more
Apple refurbished 2014 13-inch Retina MacBook...
The Apple Store has Apple Certified Refurbished 2014 13″ Retina MacBook Pros available for up to $400 off original MSRP, starting at $979. An Apple one-year warranty is included with each model, and... Read more
iMacs on sale for up to $205 off MSRP, NY tax...
B&H Photo has 21″ and 27″ iMacs on sale for up to $205 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $1019 $80 off - 21″ 2.7GHz iMac: $1189 $110 off - 21″ 2.9GHz... Read more
Sale! 16GB iPhone 5S for $1 with service
Best Buy is offering 16GB iPhone 5Ss for $1.00 with 2-year activation at a participating cellular provider. Choose free home shipping and activation, or buy online and activate during in-store pickup... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2014 MacBook Airs available starting at $679. An Apple one-year warranty is included with each MacBook, and shipping is free. These are currently the... Read more
27-inch 3.5GHz 5K iMac on sale for $2349, sav...
 Adorama has the 27″ 3.5GHz 5K iMac in stock today and on sale for $2349 including free shipping plus NY & NJ sales tax only. Their price is $150 off MSRP. For a limited time, Adorama will... Read more
Save up to $380 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $380 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 27″ 3.5GHz 5K iMac – $2119 $... Read more
iFixIt Teardown Awards 12-IInch Retina MacBoo...
iFixIt has posted its illustrated teardown of the new 12-inch MacBook Retina. They note that this new MacBook is less than half the thickness of the last Apple notebook called just “MacBook” back in... Read more

Jobs Board

*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Technical Project Manager - *Apple* Pay - A...
**Job Summary** Apple Pay is seeking an experienced technical PM to…manage the on boarding of new merchants for the Apple Pay platform in the US Within this role you Read more
Senior Identity Architect - *Apple* Pay - A...
**Job Summary** Apple , Inc. is looking for a highly motivated, innovative and hands-on senior identity architect to join the Apple Pay Engineering team. You will Read more
Program Manager, *Apple* Retail Global Tale...
…for the worldwide creation and implementation of the key talent development initiatives within Apple Retail. He or she will work closely with our Retail Corporate team, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.