Apple Darwin Manuel d'utilisateur télécharger pdf (Page 10)

“Huge” Data Objects

If your application may need random access to exceptionally large (>2GB) data sets, it is easier to support these

data sets in a 64-bit environment. You can support large data sets in a 32-bit application using memory mapping,

but doing so requires additional code. Thus, for new applications, you should carefully evaluate whether

supporting such large data sets is required in the 32-bit version of your application.

Note: It is not generally necessary to use 64-bit programming when working with files larger than

2 GB in a streaming fashion, such as when writing an audio or video application. These sorts of

applications work with only a small section of a file at any given time and thus do not generally

benefit significantly from the large address space of 64-bit computing. That said, these applications

often do benefit from the additional registers afforded by 64-bit computing on the Intel architecture.

64-Bit Math Performance

Applications that use 64-bit integer math extensively may see performance gains. In 32-bit applications, 64-bit

integer math is performed by breaking the 64-bit integer into a pair of 32-bit quantities. It is possible to perform

64-bit computation in leaf functions in 32-bit applications, but this functionality generally offers only limited

performance improvement.

Note: You do not need to transition your application to a 64-bit executable format merely because

your application performs 64-bit math. You can perform 64-bit math transparently in a 32-bit

application, albeit with slightly diminished performance.

Plug-in Compatibility

If you are writing an application, any plug-ins used by your application must be compiled for the same processor

architecture and address width as the running application. If your application needs to support 32-bit and

64-bit plug-ins simultaneously, you must do so using a helper process, such as an XPC service. To learn more,

read Daemons and Services Programming Guide.

In OS X v10.7 and later, all Apple applications shipping as part of the OS are 64-bit executables. This means

that users with 64-bit-capable computers will be running the 64-bit slice of key system components. And

beginning in OS X v10.8 and later, built-in apps are generally 64-bit-only. This means that any plug-ins (screen

savers, printer dialog extensions, and so on) that need to load in these applications must be recompiled as

64-bit plug-ins.

Should You Recompile Your Software as a 64-Bit Executable?

“Huge” Data Objects

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Apple Darwin Manuel d'utilisateur Page 10