Re: Predictable Internet Time

Tony Finch <dot@dotat.at> Tue, 28 March 2017 20:24 UTC

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Date: Tue, 28 Mar 2017 21:24:01 +0100
From: Tony Finch <dot@dotat.at>
To: Joe Touch <touch@isi.edu>
cc: =?UTF-8?Q?Patrik_F=C3=A4ltstr=C3=B6m?= <paf@frobbit.se>, Phillip Hallam-Baker <phill@hallambaker.com>, IETF Discussion Mailing List <ietf@ietf.org>, Jared Mauch <jared@puck.nether.net>
Subject: Re: Predictable Internet Time
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Joe Touch <touch@isi.edu>; wrote:
>
> When UTC adds a leap second, nothing different happens to POSIX time.

Clearly not. Either it jumps backwards at the start of the leap second, or
at the end of the leap second, or it stops for a second, or it runs slow
for some  period of time in a controlled manner (e.g. leap smear) or an
uncontrolled manner (NTP swinging around in a wild effort to resync).

The POSIX formula that specifies the translation from UTC to time_t
implies that it jumps back at the end of the leap second.
http://pubs.opengroup.org/onlinepubs/9699919799.2016edition/basedefs/V1_chap04.html#tag_04_16

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>;  http://dotat.at/  -  I xn--zr8h punycode
South German Bight, Humber, Thames: Southwesterly 4 or 5, increasing 6 at
times. Slight or moderate. Occasional rain, fog patches. Moderate or good,
occasionally very poor.