Re: [LEAPSECS] building consensus

From: John Cowan <>
Date: Sun, 4 Jun 2006 22:17:17 -0400

Zefram scripsit:

> >If this means that leap seconds and leap days are analogous, then I
> >suppose so. If it means something else, I don't understand it.
> That's what I meant. Can you suggest a clearer wording?

"Leap seconds (after 1972) are closely analogous to leap days."

> Being ambiguous between adjacent seconds seems inherently faulty to me.

The designers of Posix time thought it was more important to preserve
the property that dividing the difference between two time_t values
by 60, 3600, 86400 would give minutes, hours, days.

> Are you thinking of linear counts such as POSIX time, where the
> representation is ambiguous? I was implicitly excluding those, on the
> grounds that they don't count as a "representation". It's also not
> "linear".

No, it isn't. But that doesn't mean you *can't* construct a numerical
representation of UTC time: say, the number of UTC seconds since

> >Unix time (better: Posix time) *is* monotonically nondecreasing,
> >provided you set it with NTP and not by brute force.
> Not necessarily. The Mills kernel model makes the Unix time perform a
> backward step of 1 s during a positive leap second, and does so using
> data supplied by NTP. I've seen Linux 2.4 perform this step (but during
> a simulated leap second, not a real one) in the course of testing some
> of my timekeeping code.

Quite so; my error.

John Cowan
There are books that are at once excellent and boring.  Those that at
once leap to the mind are Thoreau's Walden, Emerson's Essays, George
Eliot's Adam Bede, and Landor's Dialogues.  --Somerset Maugham
Received on Sun Jun 04 2006 - 19:17:53 PDT

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