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

Dash 4.0.0 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
Bookends 12.7.9 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
TrailRunner 3.8.834 - Route planning for...
TrailRunner is the perfect companion for runners, bikers, hikers, and all people wandering under the sky. Plan routes on a geographical map. Import GPS or workout recordings and journalize your... Read more
iFFmpeg 6.2.5 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
DaisyDisk 4.4 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
iFFmpeg 6.2.5 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
DaisyDisk 4.4 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
BetterTouchTool 2.07 - Customize Multi-T...
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
BetterTouchTool 2.071 - 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
BetterTouchTool 2.07 - Customize Multi-T...
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

Latest Forum Discussions

See All

Pokémon GO Generation 2 evolution guide
At long last, Niantic Labs finally unleashed the Generation 2 Pokémon into the wild. Pokémon GO trainers are scrambling to grab up this new set of 80 Pokémon. There are some special new tricks required to catch all of these new beasties, though.... | Read more »
The best new games we played this week
It feels as though the New Year got off to a creaking start as far as mobile games go, but that's changed over the past few weeks. The last few days alone have seen the debut of a number of wonderful games, so we thought we'd take the time to... | Read more »
Recruit more scallywags and discover new...
Get ready to show off your sea legs all over again in Oceans & Empires’ new grand update, which aims to make the act of rising to the role of seven seas ruler even more fresh and appealing, thanks to a richness of new content on both iOS and... | Read more »
Mage the Ascension: Refuge (Games)
Mage the Ascension: Refuge 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The groundbreaking roleplaying game Mage: The Ascension manifests in our turbulent present with Refuge, an... | Read more »
Vampire: Prelude (Games)
Vampire: Prelude 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The classic roleplaying game Vampire: The Masquerade returns to digital games with a Prelude of things to come. Experience a... | Read more »
Digby Forever Guide: How to dig to the d...
Digby Forever is a sparkling homage to arcade classics, and while you may be tiring of the number of arcade games being thrown at you, this endless digger finds many ways to stand out from the rest of the pack. The game manages to be challenging... | Read more »
The best sales on the App Store this wee...
It's been quite the week in mobile games, but if the latest releases(there were some pretty darn good ones, in case you missed out) aren't really doing the trick, perhaps some of these discounted games will. Many of these premium games had their... | Read more »
Why the new Fire Emblem Heroes update sh...
It’s exciting to see Nintendo delving into the mobile sphere, regardless of whether it’s to give fans another platform to enjoy their fans or simply a sound business venture. Two of the company's announced mobile games have finally come to... | Read more »
New Fire Emblem Heroes update adds new h...
Fire Emblem Heroes received a sizeable update first thing this morning. The update features a batch of fresh content along with a few updates to the game's systems. [Read more] | Read more »
The Deep Paths (Games)
The Deep Paths 1.0 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: 25% off launch sale!!! The Deep Paths: Labyrinth Of Andokost is a first-person, dungeon crawling RPG, with traditional grid-based... | Read more »

Price Scanner via MacPrices.net

13-inch 2.0GHz Space Gray MacBook Pro on sale...
Adorama has the non-Touch Bar 13″ 2.0GHz Space Gray MacBook Pro in stock today for $100 off MSRP. Shipping is free, and Adorama charges NY & NJ sales tax only: - 13″ 2.0GHz MacBook Pro Space Gray... Read more
13-inch Touch Bar MacBook Pros on sale for $1...
B&H Photo has select 2016 Apple 13″ Touch Bar MacBook Pros in stock today and up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.9GHz/512GB Touch Bar MacBook... Read more
KSI-1802R SX Disinfect-able Keyboard With Wav...
KSI has unveiled a new, innovative medical keyboard, the KSI-1802R SX, at HIMSS 2017, running February 19-22 in Orlando, Florida. KSI-1802R SX is the only keyboard that combines dual factor... Read more
15-inch Touch Bar MacBook Pros on sale for up...
Amazon has 15″ Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP including free shipping: - 15″ 2.7GHz Touch Bar MacBook Pro Space Gray: $2720.38 $79 off MSRP - 15″ 2.7GHz... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free: -... Read more
13-inch 1.6GHz/256GB MacBook Air on sale for...
Newegg has the 13″ 1.6GHz/256GB MacBook Air (MMGG2LL/A) on sale for $1029.99 including free shipping. Their price is $170 off MSRP, and it’s the lowest price available for this model. Choose Newegg... Read more
Save up to $600 with Apple refurbished Mac Pr...
Apple has Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The following... Read more
12-inch 1.1GHz Retina MacBooks on sale for $1...
B&H has 12″ 1.1GHz Retina MacBooks on sale for $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1149 $150 off MSRP - 12″ 1.1GHz... Read more
InTouch Health Expands iOS And Windows Produc...
Specialty telehealth enterprise provider InTouch Health has announced an expanded range of FDA Class I listed medical devices and software solutions for ambulatory, non-acute and non-emergent... Read more
iMobie Airs World’s 1st iCloud Manager with M...
iMobie Inc., an Apple-related software company, announced their newly-updated iPhone manager AnyTrans with exclusive feature to sync and manage contents across multiple iCloud accounts. With it,... 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
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*Apple* Technician - nfrastructure (United S...
Let’s Work Together Apple Technician This position is based in Portland, ME Life at nfrastructure At nfrastructure, we understand that our success results from our 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
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.