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From: Sam <sah@softcardsystems.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] env walk
References: <20010509165901.CD181199E7@mail.cse.psu.edu> <01050913344601.04828@softnet>
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Date: Wed,  9 May 2001 13:39:35 -0400
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ugh...'scuse the flub.

On Wednesday 09 May 2001 13:34, you wrote:
> schweet
>
> John had looked at it on Monday and it said Showers Sat-Mon...guess the
> storm got pushed back.
>
> ... ok, I'm getting a little excited now.
>
> :)
>
> On Wednesday 09 May 2001 12:58, you wrote:
> > The n**2 comes from the ls M* walking each entry in the environment
> > with envwalk walking from the first to that entry every time.  All the
> > time is spent in the devdir+convM2D in procgen.  The
> >
> > 	for(e = eg->entries; e && s; e = e->link)
> > 		s--;
> >
> > is pretty much fleeting even for 1000 entries.  Otherwise the algorithm
> > for your example would be n**3.
> >
> > for example:
> >
> > #include <u.h>
> > #include <libc.h>
> >
> > struct X
> > {
> > 	struct X *next;
> > };
> >
> > struct X x[1000];
> >
> > void
> > main(void)
> > {
> > 	struct X *p;
> > 	int i, j;
> >
> > 	for(i = 0; i < nelem(x)-1; i++)
> > 		x[i].next = &x[i+1];
> >
> > 	for(i = 0; i < nelem(x); i++)
> > 		for(j = 0, p = x; j < i && p != nil; p = p->next, j++)
> > 			;
> >
> > }
> >
> > takes .01 seconds on my crufty old machine.
> > The advantage to your loop is that you take all the useless stuff
> > that devdir does out of the inner loop, not too mention the call
> > itself.

-- 


Sam Hopkins
------------------------------------------------
QOTD:
"Design top down, implement bottom up."