Date: Sat, 28 Mar 1998 23:21:34 +0800 From: Peter Wemm <peter@netplex.com.au> To: Michael Richards <miker@scifair.acadiau.ca> Cc: freebsd-questions@FreeBSD.ORG, freebsd-bugs@FreeBSD.ORG Subject: Re: Login accounting design Message-ID: <199803281521.XAA11722@spinner.netplex.com.au> In-Reply-To: Your message of "Fri, 27 Mar 1998 20:58:06 -0400." <Pine.BSF.3.96.980327205332.28156A-100000@scifair.acadiau.ca>
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Michael Richards wrote:
> Hi. I noticed something a little weird...
>
> [root@frodo /root]# ac -p
> root 0.56
> ftp 0.02
> miker 0.22
> jon 11.00
> total 11.80
> [root@frodo /root]# ac -p
> root 0.56
> ftp 0.02
> miker 0.22
> jon 11.00
> total 11.81
> [root@frodo /root]# ac -p
> root 0.57
> ftp 0.02
> miker 0.22
> jon 11.00
> total 11.81
>
> Someone can't add :) Well, maybe this was a 1 in a million thing where I
> happened to run the command and inbetween cpu cycles, the time changed,
> but I would think that the order of commands would be arranged such that
> the number added to the entry at the username would be the same number
> printed... Having not the time to do source digging, I am of course making
> assumptions on how the ac program was written...
>
> -MIke
I suspect that you'll find this is a rounding issue. I don't recall
exactly, but there are some 128 ticks per second timers, and these won't
map to an exact 0.01. You're probably seeing the result of all
calculations being done in 1/128ths of a second and being converted to 1/
100ths at display time.
A rough example with unrounded numbers:
1: (raw) (rounded to 1/100)
root: 0.562 -> 0.56
[the rest]: 11.242 -> 11.24
======
total: 11.803 -> 11.80
2:
root: 0.564 -> 0.56
[the rest]: 11.242 -> 11.24
======
total: 11.806 -> 11.81
3:
root: 0.566 -> 0.57
[the rest]: 11.242 -> 11.24
======
total: 11.808 -> 11.81
The raw numbers I've used would not be real 1/128 conversions, but it
should give the idea.
Cheers,
-Peter
--
Peter Wemm <peter@netplex.com.au> Netplex Consulting
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