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Top Forums UNIX for Dummies Questions & Answers Advanced info on CPU Emulators Post 302530605 by Corona688 on Tuesday 14th of June 2011 12:01:46 PM
Old 06-14-2011
Quote:
Originally Posted by theKbStockpiler
Interpreted implies that the Emulator would just be substituting code for other code from a look-up table but then the program would actually be more or less ported at this point would it not?
It's hard to call something 'ported' when it can't run outside the emulator, no.

The exact approach may depend on the emulator in question. qemu, for instance, can use CPU virtualization features if you're emulating the same architecture you're on -- setting up a virtual environment in hardware. This lets programs run in the virtual environment mostly natively, just trapping a few higher-ring instructions and the like so software can take over and fill in the gaps. This was actually possible without hardware virtualization support, but it makes it much easier and more efficient -- I'm not too well read on the details but suspect it involves more direct/explicit ways for the client to talk to the host, for starters.

For emulators that run instructions that are completely alien to the native processor, the obvious way would be to make a data structure in memory that represents the registers of the native CPU, and use something like a big switch statement or look-up table to branch to the appropriate code for each instruction. If the emulated CPU has fewer registers than the native one I suppose you could stick everything in registers, use jump tables, self-modifying code, raw ASM and other dirty tricks to make it much faster but in the end it's the same idea.
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less(3pm)						 Perl Programmers Reference Guide						 less(3pm)

NAME
less - perl pragma to request less of something SYNOPSIS
use less 'CPU'; DESCRIPTION
This is a user-pragma. If you're very lucky some code you're using will know that you asked for less CPU usage or ram or fat or... we just can't know. Consult your documentation on everything you're currently using. For general suggestions, try requesting "CPU" or "memory". use less 'memory'; use less 'CPU'; use less 'fat'; If you ask for nothing in particular, you'll be asking for "less 'please'". use less 'please'; FOR MODULE AUTHORS
less has been in the core as a "joke" module for ages now and it hasn't had any real way to communicating any information to anything. Thanks to Nicholas Clark we have user pragmas (see perlpragma) and now "less" can do something. You can probably expect your users to be able to guess that they can request less CPU or memory or just "less" overall. If the user didn't specify anything, it's interpreted as having used the "please" tag. It's up to you to make this useful. # equivalent use less; use less 'please'; "BOOLEAN = less->of( FEATURE )" The class method "less->of( NAME )" returns a boolean to tell you whether your user requested less of something. if ( less->of( 'CPU' ) ) { ... } elsif ( less->of( 'memory' ) ) { } "FEATURES = less->of()" If you don't ask for any feature, you get the list of features that the user requested you to be nice to. This has the nice side effect that if you don't respect anything in particular then you can just ask for it and use it like a boolean. if ( less->of ) { ... } else { ... } CAVEATS
This probably does nothing. This works only on 5.10+ At least it's backwards compatible in not doing much. perl v5.16.3 2013-02-26 less(3pm)
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