[LEAPSECS] Time math libraries, UTC to TAI

[John Sauter]

On Sun, 2016-12-25 at 18:53 -0800, Steve Allen wrote:
> On Sun 2016-12-25T19:37:31 -0700, Warner Losh hath writ:
> > I think that POSIX has de-facto redefined UTC, and it's time that
> > the
> > UTC standard catch up to this quiet revolution.
> 
> POSIX has defined that the time scale upon which time_t is based has
> the characteristics of every time scale other than UTC.  That is,
> there are 86400 "seconds" in a "day".  That will stay true until
> POSIX is in use for civil time somewhere else than on earth.
> 

The fact that POSIX defines a time scale different from UTC is a
problem for POSIX, not for UTC.  People use UTC in their computers, and
don't care what the POSIX standard says.

> It is less clear is what kind of "seconds" and "days" POSIX wants,
> largely because the current UTC did not make the distinction clear.
> Thus for POSIX the "seconds" being ticked and "days" of the calendar
> must be related by the factor 86400, which is not the case in UTC as
> defined by CCIR/ITU-R.
> 
> It is clear that devices implementing POSIX must rely on the time
> signals in radio broadcasts.  Too much infrastructure already exists
> which relies on those broadcasts.
> 
> It is clear that the agencies implementing the radio broadcasts will
> never return to rubber seconds, and will not approve of smears.
> 
> So the only change that can happen to the nature of radio broadcasts
> is to start counting atomic days of atomic seconds.
> 

No, that isn't the only change that can happen.  Another possibility is
that the radio broadcasts do not change and people ignore the POSIX
standard, keeping time according to UTC.  As long as you don't use
POSIX time_t, that is doable.

> It is not clear that the name UTC is sacrosanct to POSIX.
> The machines simply do not care what humans call that time scale.
> 
> It is clear that some humans do care about the name UTC.  I have not
> seen any of the agencies make arguments about why the radio broadcast
> time scale cannot change its name.  It has done so in the past, and
> the world did not care.
> 
> --
> Steve Allen                    <sla at ucolick.org>              WGS-84
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