[time-nuts] Leap Quirks

M. Warner Losh imp at bsdimp.com
Sun Jan 4 00:54:35 EST 2009


In message: <495FF91C.60401 at rubidium.dyndns.org>
            Magnus Danielson <magnus at rubidium.dyndns.org> writes:
: M. Warner Losh skrev:
: > In message: <m3mye8qen3.fsf at lugabout.jhcloos.org>
: >             James Cloos <cloos at jhcloos.com> writes:
: > : >>>>> "Warner" == M Warner Losh <imp at bsdimp.com> writes:
: > : 
: > : Jim> By which sequence?
: > : 
: > : Warner> The sequence where midnight % 86400 isn't 0.
: > : 
: > : MY appologies, but that isn't narrowing it for me.  POSIX only cares
: > : about POSIX midnight, not UTC midnight, so the fact that it was already
: > : past PODIX midnight when the leap second and UTC midnight happened is
: > : irrelevant to POSIX.
: > 
: > posix midnight and utc midnight are the same things.  You had said
: > that the system time was returned as ....24 at UTC 2009-01-01
: > 00:00:00, which isn't posixly correct.
: 
: Um... no. That's the hacked POSIX interpretation, not the POSIX standard.
: 
: We have at least three POSIX interpretations here.
: 
: One which has UTC rubber seconds from 1970 to 1972 and from then true SI 
: seconds from 1972.
: One which has true SI seconds from 1970.
: One which has UTC tracking in pieces and is slid "sideways" to make 
: midnight match UTC midnight.
: 
: The two first ones is interpretations of POSIX over UTC variations. The 
: third one is a hack of POSIX to make it kind of work anyway with NTP. 
: Only with the third interpretation POSIX midnight and UTC midnight is 
: the same.
: 
: Now, which of them is "right"?

Midnight must be xxxx00.  POSIX says so explicitly because leap
seconds do not exist in POSIX.  The committee has issued a very
explicit addendum to this effect.

Which one is more desirable?  Well, that's a matter of debate, but
which one is POSIXly correct isn't.

Warner




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