The brains behind Apple's Rosetta: Transitive

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how to make a fast code translation

First of all, Richard Flude's point about the program spending
80%+ of the time in the OS is a valid point that I was going to
make.
The other point is that, in a binary, all the entry points are
generally labelled, and therefore branch points are discoverable.
It is pretty easy to replace machine code from one CPU with the
machine code of another CPU if you can amend the branch
addresses. (even calculated ones).
I get the feeling rosetta is an emulator, whereas I'm talking
about something like a JIT compiler, which compiles java
bytecode to machine code for the host processor.
The difference would be, like the early Jikes, you simply keep the
JIT compiled output forever.
There will be sequences of translated code that is wasteful, but
these can be identified purely in binary pattern terms, and
therefore optimised out.
So frankly, I'd be amazed if one couldn't get to the stage where
there was (for equivalent MIPS) only something like a 5% drop in
performance. As the x86 generation CPUs that apple will use will
likely be faster than exisitng CPUs, then the upgrader will
probabaly still see his old apps run faster (until he downloads
the x86 binary).
Apple could make the transition easier by giving a tool that goes
away, finds all the installed apps, and downloads the x86
versions instead.

Posted by: hipparchus2000   Posted on: 06/10/05 You are currently: a Guest | Members login | Terms of Use

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