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Re^4: Speed/Efficiency tweaks for a fannkuch benchmark script?

by robin (Chaplain)
on Dec 01, 2005 at 19:30 UTC ( #513396=note: print w/replies, xml ) Need Help??


in reply to Re^3: Speed/Efficiency tweaks for a fannkuch benchmark script?
in thread Speed/Efficiency tweaks for a fannkuch benchmark script?

It also fails for $n == 3, where the answers should be 231 and 312, each of which take 2 steps.

So just do || @$copy <= 3, one might say; and indeed that would give the right answers. But how do we know it would give the right answers, except by comparing the output with the unoptimized version? Is it possible to prove that this is safe?

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Re^5: Speed/Efficiency tweaks for a fannkuch benchmark script?
by thundergnat (Deacon) on Dec 01, 2005 at 19:39 UTC

    Ah. Yes, ok I see your point now. I might be able to make a case for n being in the first position being safe to ignore, but how to prove when 1 is in the last...

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[Corion]: Maybe doing a double-fork (daemonizing) can make go that information away, but maybe not
[Corion]: But I think my knowledge of unix/Linux datastructures is several decades out of date, so I don't really know what information it keeps on processes
[oiskuu]: The useful bits that relate to your process can be found under /proc/self. What information are you thinking of? Tty name?
[tye]: I just daemonized and getlogin() still knew who I had been.
[tye]: perhaps loginuid ? Not that I concede that something not being in /proc means it is not useful.
[Corion]: tye: That's really interesting, but maybe it is because getlogin() returns the name, or the uid, so if that user has been replaced by another user with the same uid in the meantime, that's no problem to the system...

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