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From: Don Lewis <truckman@FreeBSD.org>
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Cc: src-committers@FreeBSD.org, andre@FreeBSD.org, bde@zeta.org.au,
	cvs-src@FreeBSD.org, cvs-all@FreeBSD.org, phk@phk.freebsd.dk
Subject: Re: cvs commit: src/usr.bin/vmstat vmstat.c src/usr.bin/w w.c 
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On 20 Oct, M. Warner Losh wrote:

> Leaving aside the leap table issue for the moment, there's a more
> fundamental problem.  You cannot possibly compute correct answers for
> times that are in the future, even a little ways in the future.  What
> if time1 is June 30, 2006 23:59:58 and time2 is July 1, 2006 00:00:01.
> While neither of these seconds are ambiguous, no one on the planet can
> say today, with certainty, what the answer will be.  We have to wait
> until early January when IERS issues the next Bulletin C.

There's a similar problem with computing time differences across
daylight savings change transitions, since the date of the transition
and even whether there will be a transition is subject to political
whim.