TweetFollow Us on Twitter

Feb 97 Tips

Volume Number: 13 (1997)
Issue Number: 2
Column Tag: Tips & Tidbits

Tips & Tidbits

By Steve Sisak

I hope this surprises at least some readers and helps avoid a bug or two. Here's a self-test to see what you know about subtraction. Be honest.

On a PPC chip, which of the following sets the carry bit (assuming an instruction form that sets the carry is used)?

a) 0 - 0

b) 0 - 1

On a 68K chip, which sets the carry?

c) 0 - 0

d) 0 - 1

Did you answer (a) and (d)? That's right. Subraction is defined differently on PPC than on 68K, which might catch you off guard, especially if you're an old hand at 68K asm.

On 68K, sub d0,d1 is defined as d1 = d1 - d0, and the carry behaves like a simple borrow. However, PPC makes direct use of the definition -n = NOT(n) + 1 and, subf r5,r3,r4 is defined as r5 = r4 + NOT(r3) + 1, making the XER[CA] bit (for instructions that update it) reflect an addition carry instead of a borrow.

This difference propagates to extended subtraction. You would do extended subtraction similarly on either chip.

68K:

1) sub low words.

2) subx high words.

PPC:

1) subfc low words.

2) subfe high words.

However, the internal details are different.

subx d0,d1 --> d1 = d1 - d0 - X bit.

subfe r5,r3,r4 --> r5 = r4 + NOT(r3) + XER[CA].

There are many other examples where the carry works completely differently on the two chips (e.g., arithmetic right-shifts).

68K: carry is set (for any type of source) if and only if the LAST bit shifted out of the right was a one.

PPC: carry is set only if the source was negative and ANY ones are shifted out of the right.

Yes, it's all in the manuals, but who reads manuals?

Bill Karsh
billKarsh@aol.com

1) When patching a libraray, _Open needs more param block fields cleared than does _OpenDF.

2) when changing the font of a (popup) menu by hooking the MDEF, LastSPExtra must be set to -1 to clear the font cache both before calling the MDEF and after restoring the font stuff.

Tony Nelson
tonyn@tiac.net

Having trouble getting Apple Menu Options' hierarchical menus to show? You may not have called MaxApplZone() early in your application. The various patches AMO installs require sufficient heap to draw the menus; if you don't expand your heap to its maximum early on, the patches may not have the right amount of memory available when first called, and your hierarchical Apple menu will not draw.

Brian Bechtel
blob@apple.com

Apple's System 7.5.3 (aka System 7.5 Update 2.0) adds a slick new way to quickly get around while in a StandardFile dialog. While the dialog is up, click on the desktop or any folder open on your desktop. You did not receive the annoying beep you expected as in 7.5.1 and earlier - instead, StandardFile took you right to that directory! This is invaluable when you have your deeply-nested work folder opened on the desktop and StandardFile decides to stick you in some remote location. Now anything visible is one click away! If Apple would give us the new movable modal file dialogs, we could really take advantage of this. These are coming in Copland, but I am hoping they will appear in System 7.6 that has OpenDoc built-in.

Bill Hayden
nikol@codewell.com

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

NTFS 14.3.318 - $19.95
This latest version supports the new macOS 10.12 Sierra! NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and... Read more
iFFmpeg 6.2.2 - 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
ForeverSave 2.1.6 - Universal auto-save...
ForeverSave auto-saves all documents you're working on while simultaneously doing backup versioning in the background. Lost data can be quickly restored at any time. Define your preferred time... Read more
BetterTouchTool 1.961 - 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
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Postbox 5.0.9 - Powerful and flexible em...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
DiskCatalogMaker 6.5.16 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more

Latest Forum Discussions

See All

Silent Depth Submarine Simulation (Game...
Silent Depth Submarine Simulation 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: | Read more »
Enneas Saga lets you lead your own demon...
Defend the land of Enneas Continent from the forces of evil in the new fantasy MMORPG from Lyto Mobi: Enneas Saga. Can’t wait? No problem. It’s available to download now on Android devices. | Read more »
Great zombie games in the spirit of Dead...
Dead Rising 4 arrives tomorrow, giving enthusiasts a fresh chance to take selfies with zombies and get up to other ridiculous end-of-the-world shenanigans. To really get into the spirit of things, we've gone and gathered the best zombie games that... | Read more »
Amateur Surgeon 4 Guide: Advanced tips a...
Amateur Surgeon 4 is still tackling the competition at the top of the App Store charts, so if you haven't tried it out yet, you should probably do that right away. If you've been at it for a while, though, perhaps you're ready to start expanding... | Read more »
Amateur Surgeon 4 Guide: Become the worl...
It's time to wield your trusty pizza cutter again, as Amateur Surgeon has returned with a whole fresh set of challenges (and some old, familiar ones, too). Starting anew isn't easy, especially when all you have at your disposal is a lighter, the... | Read more »
Le Parker: Sous Chef Extraordinaire (Ga...
Le Parker: Sous Chef Extraordinaire 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Telltale Games really is working on a Gu...
Telltale Games' next episodic adventure is indeed Guardians of the Galaxy. A document tied to the voice actors strike suggested that the project was in the work, but now we have direct confirmation following an announcement at the Game Awards that... | Read more »
Amateur Surgeon returns to iOS and Andro...
Amateur Surgeon and its two sequels disappeared from the App Store some time and it was sad days for all. But now, just in time for the holidays, the Adult Swim favorite makes its joyous return in the shape of Amateur Surgeon 4, a remake with... | Read more »
The best board games on mobile
Sometimes you need to ditch all of the high speed, high action games in favor of something a little more traditional. If you don't feel like parting ways from your mobile device, though, there are still plenty of ways to get that old-school fix.... | Read more »
The best Facebook Messenger Instant Game...
Facebook's new Instant Games is now here, meaning you can play games with your friends directly via Facebook. It's a fun new way to connect with friends, of course, but it's also proving to be a solid gaming experience in its own right, with a... | Read more »

Price Scanner via MacPrices.net

Slate Tablet Market Share to Fall Below 75% i...
After two years of decline, the tablet market is showing signs of new life as productivity trumps entertainment, and tablets become cost-effective computing devices for both entertainment and... Read more
Yostand Launches Indigogo campaign for iStand...
China-based startup Yostand (meaning ‘your stand’), has announced the launch of its Indigogo campaign for their newly awaited iStand7. This product is a one of a kind iPhone battery case that offers... Read more
Green App – Budget Forecasting Now Available...
Indianapolis, Indiana based CoopToons has announced the release of Green – Budget Forecasting 1.5, an update to their personal budgeting app developed exclusively for iOS devices. Green aims to be a... Read more
New 2016 13-inch 2.0GHz MacBook Pros in stock...
Overstock.com has the non-Touch Bar 13″ MacBook Pros in stock today for $150 off MSRP. Shipping is free: - 13″ 2.0GHz MacBook Pro Space Gray (MLL42LL/A): $1349.99 $150 off MSRP - 13″ 2.0GHz MacBook... Read more
15-inch 2.6GHz Silver Touch Bar MacBook Pro o...
Adorama has the new 2016 15″ 2.6GHz Silver Touch Bar MacBook Pro (MLW72LL/A) in stock and available for $2349 including free shipping. Adorama charges sales tax in NY & NJ only. Their price is $... Read more
13-inch MacBook Airs on sale for up to $180 o...
Overstock.com has 13″ MacBook Airs on sale for up to $180 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (MMGF2LL/A): $869.99 $130 off MSRP - 13″ 1.6GHz/256GB MacBook Air (sku... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros (MD101LL/A) available for $829, or $270 off original MSRP. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook... Read more
Monday roundup of Holiday Mac sales: Up to $3...
Take up to $300 off MSRP on the price of a new Apple Mac at B&H Photo today as part of their Holiday sale. Shipping is free, and B&H charges NY sales tax only. Touch Bar MacBook Pros are in... Read more
12-inch WiFi Apple iPad Pros on sale for up t...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for up to $50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP... Read more
9-inch Apple WiFi iPad Pros on sale for $20-$...
B&H Photo has 9.7″ Apple WiFi iPad Pros on sale for $20-$50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 9″ Space Gray 256GB WiFi iPad Pro: $779.95 $20 off MSRP... 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
Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 53586123 Pittsburgh, Pennsylvania, United States Posted: Nov. 28, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC Read more
*Apple* Retail - Multiple Positions- Plano,...
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- Kansas...
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- Chicago...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.