Re: Machine code parsers (entropy of machine code)

Derek M Jones <derek@knosof.co.uk> wrote


> I think that perhaps we can talk about the entropy of instruction
> sets. But the code egnerated by different compilers?


Actually, the entropy of the instruction sets for Intel/PowerPC was
one of the initial questions. The set of compilers can be fixed saying
that we take only Microsoft compilers into consideration. I don't
believe this matters a lot, though.


> I once did a little experiment. I measured how well gzip compressed
> executable programs for a vareity of machines. There did seem to
> be some correlation between compression ratios for the same programs,
> compiled for different cpu's.


Well, you see, the gzip compression of executable code cannot give you
a good idea about the entropy of the machine code, because gzip
compresses everything as raw data.


As for different CPUs I'd expect RISC code to have smallest entropy
(compresses best).


> Do you think optmised code will have a higher or lower entropy?


It's hard to say, I'd expect higher than non-optimized, because
usually some redundancies are removed during the optimization.


Andrey
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