TweetFollow Us on Twitter

Portability
Volume Number:9
Issue Number:10
Column Tag:Software design

Related Info: Memory Manager File Manager

Beyond the Macintosh

Here’s a way to design your code to be portable

By Lala “Red” Dutta, DataViz, Inc.

Here we are... 1993 and the playing field has narrowed down to a handful of machines and architectures. The contenders left on the field are Unix boxes, PC’s and Mac’s. However, soon to enter the playing field is the Power PC based Macintosh. And where are we? Since the majority of MacTech readers are Macintosh programmers, it is safe to assume... “We’re On A Macintosh!” (And I say that while making some Tim Allen grunts)

But for a moment, let me state a few observations of mine...

• Macintosh programmers know what the game really is... “Make something obvious and simple, and people will use it.”

• Wouldn’t it be nice if we could show the rest of the world how to write a better application?

• Wouldn’t it be nice if we made lots of money selling this stuff to the unenlightend?

So with those observations, let me ask the million dollar questions... Is your code portable? Will you be able to recompile and run on the Power PC? And what about Windows and OS/2? Can you recompile and run there too? After all, if you can do that, you can make money on many fronts!!! (Mo’ Money, Mo’ Money, Mo’ Money!)

At this time, I want to make a couple of statements about what’s up and coming, and what’s not! A lot of gratuitous code will not be present! After all, we’re all adults, and we’re bright enough to code this stuff on our own! (We don’t need no stink’in code!) You can also expect to see quotes from many movies and sitcoms. Also, even if you’re not a techie, you should have no problem understanding the gist of what I’ll be talking about (although a vague idea about C and C++ would help).

Zen And Portability

Before we can walk down the golden path, we need to have an objective. So here is the line my co-workers are use to hearing me say...

If truly portable code is written, it can be used anywhere, any time, and in any form.

So there’s the target we wish to hit. But now to get back to the real world, we know we can’t hit that 100% of the time. So the true key is to separate what can hit that target from that stuff which cannot. To get a little more specific, we need to achieve the following:

• Create platform independent code that relies on other platform dependent code to do the dirty work.

• Have uniform API’s between the platform dependent and independent code.

• Ensure that the platform independent code is completely insensitive to the underlying hardware and operating environment.

• Ensure that the platform dependent code has a completely general interface and takes full advantage of the underlying hardware and operating environment.

• Finally, ensure that portability is retained through maintenance.

Portability Overview

So what does this all mean? Hopefully, this diagram clears things up a little bit:

With this type of model, your core code deals with doing the main task at hand. It then relies on other code to take care of the platform specific stuff. So what kind of things go in each group of code? It really is entirely your choice, but this happens to be my model:

Environment Manager TApplication, InitApp, MaxApplZone

User Interface Manager TWindow, TLists, TButton, TStatic,

DrawRect, DrawCircle, Line, etc...

I/O Manager NewFile, OpenFile, CloseFile, Read,

Write, Seek, Tell, etc..

Memory Manager AllocHandle, FreeHandle,

AppendToHandle, HandleSize, etc...

Another preference of mine is to have C++ classes and objects in the Environment and User Interface managers. Also, I prefer standard C routines for I/O and Memory Management. However, you can do whatever you are comfortable with.

Finally, I prefer to keep sub-folders (or sub-directories that contain the non-portable code. This way my main folder (or directory) contains only the portable code. I also prefer keeping everything on a Macintosh server (because of resource forks). Then I can have a batch file that mounts the volumes that contain all the code, copies what I need, and starts the makefile. On the Mac, I can just use a makefile.

Portable Data Types

One of the most prevalent problems in portability is data. (Red’s proverb on cross-platform computing: “one machine’s garbage is another machine’s data.”) What do I mean... byte order and data size. The Motorola and Intel chips store numbers in reverse order from each other. For example, lets say I have a long unsigned integer with the value 110 (hex 6E). On the Motorola, it would exist as 0x0000006E. On an Intel machine, it would exist as 0x6E000000.

Another problem to keep in mind is the size of data types. For instance, what is the size of an ‘int’ under MPW, Think, or Microsoft? Are they all the same size? And moreover, what is the size of a ‘double’ under all those compilers?

And now for the clinchers... is a Handle always a pointer to a pointer? Is a Handle always four bytes? Does a pointer always point to the right segment?

So how do we get around these problems. Actually, the solution is pretty easy. What you need a set of data types that have the same meaning regardless of their native environment. You can achieve this by having an include file (I usually call it defTypes.h) for each platform which defines some standard types:

Byte Single byte signed character

UByte Unsigned single byte

Word Two byte signed integer

UWord Two byte unsigned integer

Long Four Byte signed integer

ULong Four Byte unsigned integer

Float64 64 bit IEEE Float

Float80 80 bit IEEE Float

Pointer Pointer to an absolute address

Handle Token for relocatable space

etc...

Now lets take some real world examples. If I were under Think C and I had to use 64 bit IEEE floats, I would typedef Float64 as a short double. If I were under MPW and I needed a two byte integer I would typedef Word as a short. If I needed a pointer under Borland C, I would typedef Pointer as a (void far *). This way I can have a known data type and definition under each platform.

Additionally, I have routines that take a Pointer to a certain data type and returns the data in its native form. These routines include:

/* 1 */

Word            macword(Pointer p);
Long             maclong(Pointer p);
Float64        macFloat64(Pointer p);
Float80        macFloat80(Pointer p);
etc...
Word            pcword(Pointer p);
Long             pclong(Pointer p);
etc...

Each routine describes the type of data it uses as an argument. For example whenever I use the function pcFloat64, I’m saying that the thing p points to is a 64 bit pc based IEEE float and I want a native 64 bit float returned. So what does the code look like?

/* 2 */

// Borland Implementation of pcFloat64
Float64 pcFloat64(Pointer p)
{
 return *((Float64 *) p);
}


// MPW Implementation of pcFloat64
Float64 pcFloat64(Pointer p)
{
 Float64f;

 revmem(p, (Pointer) &f, 8);// reverses p onto f
 return f;
}

Notice how the Macintosh implementation needed to reverse the data in order to use it. And since the PC implementation already had it in its required form, it merely sent the value along.

Finally, how do we manipulate this data. Generally, I have a library of platform independent routines that do the following:

/* 3 */

myGetc(TBuff)  Get one byte from a buffer
myGetN(TBuff, Ptr, Word)  Get n bytes, put it at Ptr
myGetw(TBuff)  Get a word from a buffer
myGetl(TBuff)  Get a long from a buffer
etc...
myPutc(TBuff, Byte)Put one byte into a buffer
myPutN(TBuff, Ptr, Word)  Put n bytes into a buffer
myPutw(TBuff, Word)Put a word into a buffer
myPutl(TBuff, Long)Put a long into a buffer
etc...
// TBuff is a C++ class

Inside each of these routines, they would read the data in it’s actual form, and return the value in it’s native (or default form). So lets look at the following platform independent code that fetches a long integer from a pc based spreadsheet file:

/* 4 */

Long  myGetl(TBuff b)
{
 UByte  d[4];
 Long x;

 myGetN(b, (Pointer) d, (Word) 4);
 x = pclong((Pointer) d);

 return x;
}

Remember this code is platform independent! However, it does call pclong which has a platform independent interface, and platform dependent code.

Code Fragments And Re-Entrancy

Of course there is more to life than just applications. In the real world there are code resources, shared libraries, and dynamically loaded libraries. These code fragments are really good for localization or creating sub-applications. Or even if you wanted to create different libraries that several applications could share, they are good for that too. The topic of re-entrancy becomes prevalent if you are talking about having several applications share code at run-time. At that point, you cannot have any critical global data. (Not gonna do it! Can’t do it! Wouldn’t be prudent! Thousand Points of Light!)

But back to the issue at hand, we need to break these things down into their portable and non-portable parts and still be able to build these things as any of the three types of code fragments. Also, to be able to build code as any of the three types, we need to satisfy the most stringent requirements of all three. So let’s discuss some of the requirements of each of these types of code fragments:

Code Resources - One main entry point and must be under 32K. Also, under MPW it cannot have global data space. While under Think it may use global data space.

DLLs - Can have multiple entry points and can have global data.

Shared Libraries - These are equivalent to DLLs, but are only available under MPW. The biggie is that it will be available on the PowerPC.

So what are the overall requirements? We need code that has no global data space and is under 32K. Furthermore, it can have only one entry point. This isn’t too bad. If anybody has written any control panel devices you know how to get away without using global data and having only one entry point. Furthermore, we can also break our big code fragments into several smaller fragments. After all, isn’t that the definition of a code fragment? So we’re going to use the Macintosh Control Panel as our overall model.

But how do you do it? Well, this takes a little more finesse. Let’s go back to our original diagram of platform independent code. But now imagine that we put a platform specific front end (and export module for shared libraries). Also, we must create a standard calling sequence for using these fragments. I prefer the calling sequence described below:

OSErr fragMain (Word instruction, Pointer ctlStruct)

I use instructions for things like fragOpen, fragClose, fragDoTask, etc., and I use ctlStruct as a bucket for whatever I want to pass into and out of a fragment. Here is an example of a ctlStruct:

/* 5 */

typedef struct fragCtl {
 Word   paramCnt;
 PointerparamList;
 Handle fragWorkSpace;
} fragCtl;

And the way the fragMain would be laid out is as follows:

/* 6 */

OSErr fragMain (Word instruction, Pointer ctlStruct)
{
 OSErr  rc = noErr;

 switch (instruction) {
 case fragOpen:
 ctlStruct->fragWorkSpace = 
 AllocHandle (sizeof(mySpace));
 rc = MemErr();
 break;
 case fragClose:
 FreeHandle(ctlStruct->fragWorkSpace);
 rc = MemErr();
 break;
 case ...
 case ...
 default:
 rc = unknownFragInstruction;
 break;
 };

 return rc;
}

Remember you are free to have any types of calls you want. I’m just giving you an example of what can be done. At any rate, now that we have platform independent code for a fragment, how do we construct this stuff in the fragment type we need? Actually, this is the easy part. I have a header file that gets included that simple states the following:

/* 7 */

// Think C fragment Front End
#ifdef CodeResource
OSErr main (Word instruction, Pointer ctlStruct)
{
 Handle self;
 OSErr  rc;

 RememberA0();
 SetUpA4();
 asm  {
 _RecoverHandle
 move.l a0,self
 }
 HLock(self);  /* Don't move while running   */

 rc = fragMain (instruction, ctlStruct);

 HUnlock(self);
 RestoreA4();

 return rc;
}
#endif

And as far as shared libraries are concerned, I have a file called fragMain.exp which contains:

exports = extern fragMain;

For more details on Apple’s Shared Library Manager, you can contact Apple’s Developer Support.

Non-Portable Code

Let’s take a quick look back at our assertion about non-portable code. That assertion was to “insure that the platform dependent code has a completely general interface and takes full advantage of the underlying hardware and operating environment.”

Let’s also look back at the example of the pcFloat64 code. This is a good example of code that is platform dependent, yet has a completely platform independent interface. This makes life easy for the caller.

Now I want to take that concept one step further. Let's say I am working on the user interface part of my application. What I want is to create a TButton class for each platform that implements a regular push button. After all, I want to use push buttons. To get really specific, let’s look at Borland’s Object Windows Library.

Wouldn’t it be nice if we could have Borland’s OWL on all platforms? Actually, we can! All it takes is us rolling up our sleeves a little and creating these UI Libraries for all of the platforms we wish to support. Overall, we want C++ objects for the following user interface metaphors:

TWindow Put up a blank window

TMenu Object for a menu list

TPopUp Object for a pop up list

TScrollList Object for a scroll list

TList Create a list for scrolling, pop ups...

TCheckBox Standard check boxes

TButton Standard push buttons

TRadioButton Standard radio buttons

etc...

These C++ classes should have member functions that do whatever it is that you want. For instance, let’s take TButton. For TButton you need a constructor, a destructor, a hilite metaphor, disable metaphor, enable, and whatever else you may want.

You can take the same principles and extrapolate them for file management and memory management. However with those items, I prefer having straight C routines instead of C++ classes. (Give it to me straight Doc!)

Portable Code

Believe it or not, at this point, writing platform independent code is almost elementary. The only thing you need to do is to call your UI Manager for user interface work, call your file manager for I/O, call your memory manager for memory usage, and don’t call anything platform specific.

I know you’re saying “easier said than done.” At first it is easier said than done. But once your libraries are created, the problem is much easier the next round. Moreover, once you get into the habit, it becomes very easy. And the knowledge of what is portable, and what is not becomes more apparent. Moreover, I hope I have given you some ideas to think about and some plans to go cross-platform. And for the big Macintosh payoff, hopefully, you can position yourself well so compiling for the native PowerPC is trivial.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Printopia 3.0.4 - Share Mac printers wit...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad, or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
Tinderbox 7.3.1 - 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
ExpanDrive 6.1.6 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
VOX 3.0.1 - Music player that supports m...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
Merlin Project 4.3.3 - $289.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
Mac DVDRipper Pro 7.1 - Copy, backup, an...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
iMazing 2.5.2 - Complete iOS device mana...
iMazing (was DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and from... Read more
Pinegrow 4 - Mockup and design webpages...
Pinegrow (was Pinegrow Web Designer) is desktop app that lets you mockup and design webpages faster with multi-page editing, CSS and LESS styling, and smart components for Bootstrap, Foundation,... Read more
iExplorer 4.1.11 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Merlin Project 4.3.3 - $289.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more

Latest Forum Discussions

See All

The best mobile games to play while your...
Thanksgiving is a time to reconnect with loved ones, eat lots of food, and all of that jazz, but once the festivities start to wind down, folks tend to head to the couch to watch whatever football is happening for Turkey Day. | Read more »
The best Black Friday deals for Apple ga...
Black Friday is hours away at this point, but many popular retailers are getting a jump on things with plenty of pre-Black Friday sales already available. Many of those early bird sales including some sharp discounts on the latest Apple phones... | Read more »
The Inner World 2 (Games)
The Inner World 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Solve mind-bending puzzles in a world full of mystery and save the family of the flute-noses! Their dynasty has been... | Read more »
warbot.io wants you for the robot wars
Fans of epic gundam-style battles will find a lot to love in warbot.io, the first game for up and coming developer Wondersquad. The game saw a lot of success when it first launched for browsers and Facebook, and now even more people are getting the... | Read more »
Uncover alien mysteries in cross-genre s...
If the Alien franchise taught us anything, it’s that landing on a strange planet at the behest of a faceless corporation is probably asking for trouble. And Eldritch Game’s Deliria doesn’t prove otherwise. In 2107, Dimension LG7 is rich with... | Read more »
The best mobile games to play during dre...
| Read more »
Animal Crossing: Pocket Camp beginner...
Animal Crossing: Pocket Camp, was just announced yesterday, but it's already in soft launch in Australia. No matter where you are in the world, you can still get access to the soft launch on iOS, so we've devised a few beginner tips for folks who... | Read more »
The mobile gamer's guide to Black F...
We're starting to catch wind of some exciting deals in the mobile gaming space for Black Friday. There are big discounts on mobile phones and accessories cropping up already, so you might want to get a move on things ahead of the big day. It's... | Read more »
The best pre-Black Friday deals - Novemb...
Black Friday will soon be upon us, but online retailers are already getting a headstart on the steep discounts. Don't wait until Friday—you'll find some pretty good deals all over the internet without waiting in lines or competing with other... | Read more »
Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »

Price Scanner via MacPrices.net

Black Friday 2017: Find the best deals and lo...
Scan our exclusive price trackers for the latest Black Friday 2017 sales & deals and the lowest prices available on Apple Macs, iPads, and gear from Apple’s authorized resellers. We update the... Read more
Black Friday: 27″ 3.4GHz iMac for $1599, save...
Amazon has the 27″ 3.4GHz Apple iMac on sale for $1599.99 as part of their Black Friday sale. That’s $200 off MSRP, and shipping is free. Their price is currently the lowest price available for this... Read more
Black Friday: 13″ 2.3GHz/256GB MacBook Pro fo...
Amazon has the 13″ 2.3GHz/256GB Apple MacBook Pro on sale for $1299.99 as part of their Black Friday sale. Shipping is free: – 13-inch 2.3GHz/256GB Space Gray MacBook Pro (MPXT2LL/A): $1299.99 $200... Read more
Black Friday: 15″ 2.9GHz MacBook Pros for $25...
Amazon has lowered prices on Silver and Gray 15″ 2.9GHz MacBook Pros to $2549.99. That’s $250 off MSRP, and shipping is free. Their prices are the lowest available for these models from any reseller... Read more
Lowest Black Friday prices on Apple MacBooks:...
Save $150-$420 on the purchase of a MacBook Pro, MacBook, or MacBook Air this Black Friday and Holiday weekend with Certified Refurbished models at Apple. In many cases, Apple’s refurbished prices... Read more
Black Friday: Apple Watch Series 1 for $70 of...
Macy’s has discounted Series 1 Apple Watches by $70 on their online store as part of their Black Friday sale: – 38mm Series 1 Apple Watch: $179, $70 off – 42mm Series 1 Apple Watch: $209, $70 off... Read more
Apple offers 2016 13-inch MacBook Airs, certi...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
Black Friday sale: Mac minis for $100 off MSR...
B&H Photo has Mac minis on sale for up to $100 off MSRP as part of their Black Friday sale, each including free shipping plus NY & NJ sales tax only: – 1.4GHz Mac mini: $399 $100 off MSRP – 2... Read more
Use your Apple Education discount to save up...
Purchase a new Mac using Apple’s Education discount, and take up to $300 off MSRP. All teachers, students, and staff of any educational institution with a .edu email address qualify for the discount... Read more
Adorama posts Black Friday deals on Apple Mac...
Adorama has posted Black Friday sale prices on many Macs, with MacBooks and iMacs available for up to $200 off MSRP. Shipping is free, and Adorama charges sales tax in NJ and NY only: MacBook Pros... Read more

Jobs Board

Business Development Manager, *Apple* Pay -...
# Business Development Manager, Apple Pay Job Number: 112919084 Santa Clara Valley, California, United States Posted: 18-Aug-2017 Weekly Hours: 40.00 **Job Summary** Read more
Digital Marketing Media Planner, *Apple* Se...
# Digital Marketing Media Planner, Apple Services Job Number: 113080212 Culver City, California, United States Posted: 03-Oct-2017 Weekly Hours: **Job Summary** 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
Business Development Manager, *Apple* Pay -...
# Business Development Manager, Apple Pay Job Number: 112919084 Santa Clara Valley, California, United States Posted: 18-Aug-2017 Weekly Hours: 40.00 **Job Summary** Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 56553863 North Wales, Pennsylvania, United States Posted: 17-Jun-2017 Weekly Hours: 40.00 **Job Summary** Are you passionate Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.