Re: Predictable Internet Time

Tony Finch <dot@dotat.at> Tue, 03 January 2017 23:14 UTC

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From: Tony Finch <dot@dotat.at>
To: Joe Touch <touch@isi.edu>
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Subject: Re: Predictable Internet Time
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Date: Tue, 03 Jan 2017 23:14:20 +0000
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Joe Touch <touch@isi.edu>; wrote:

>

> Leap seconds are still seconds, which are counted in "seconds since

> epoch".



Can you you show me where in the POSIX spec linked below leap seconds
are counted? I thought they were not.


> > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16


> > $ perl -MPOSIX -e 'print strftime "%F %T\n", gmtime 1483228799'

> > 2016-12-31 23:59:59

> > $ perl -MPOSIX -e 'print strftime "%F %T\n", gmtime 1483228800'

> > 2017-01-01 00:00:00

>

> In would presume that the same code would generate a time that is one
> second behind UTC right now.



I'm not sure what you mean. If you add (24+24+23)*3600 seconds to
1483228800 you get 23:00:00 today, which is the same length of time
after 2017-01-01 00:00:00. Nothing is one second behind now. Except it
has taken me more than 600 seconds to write this message.


> I.e., the Posix code is incorrect in claiming it reports UTC.



Yes, I agree.



> NTP reports seconds since epoch; it is in the conversion of that value
> to display time that the issue of leap seconds comes into play. In
> that
> case, some systems report 59-59-00 and others 59-00-00, i.e,
> repeating a
> UTC value to account for the leap second in the human-readble output.
> Internally, the number of seconds which have passed is correct and

> include the leap second.



But if the count of seconds includes the leap second, surely the number
representing the leap second could be printed properly as :60 ?


Tony.

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