[LEAPSECS] Look before you don't leap

Joseph Gwinn joegwinn at comcast.net
Wed May 20 09:28:22 EDT 2015

On Tue, 19 May 2015 22:02:18 -0700, Rob Seaman wrote:
> On May 19, 2015, at 1:39 PM, Joseph M Gwinn <gwinn at raytheon.com> wrote:
>> In short, POSIX systems have to be able to work in a cave, with no 
>> access to the sky or knowledge of astronomy.
> If the cave has access to NTP it has access to the IERS.

Not necessarily.  One can have only local clocks, and need only 
synchronization within the cave.

> And astronomy happens underground as well:
> 	http://www.atlasobscura.com/places/sudbury-neutrino-observatory

We don't have large enough caves.  Wasn't that FTL neutrino debacle due 
to a bad connector in the time distribution path from GPS upstairs to 
the neutrino detectors downstairs?

> Astronomers and others rely on both solar and atomic timescales.  
> Both need transport infrastructure to the most remote locations on 
> Earth (and under it and in orbit).

True but not relevant to the intent of the POSIX Timescale.

> On the other hand, the one thing we can be sure about POSIX is that 
> it will ultimately have a finite lifespan.  But a day on Earth (and 
> on Mars and Pluto) will always be a synodic (mean solar) day, 
> whatever decision is made at WRC-15.

Nothing lives forever, not even the Earth, so what's the point?

As for the format of time_t, it is an integer of unspecified size.  
Most current systems use 32 bit integers, and this will roll over in 
2038 (if signed).  This was well understood back when POSIX had its 
last revision, where the omission of a size was intentional.  

The rationale is that by the time we get to 2038, all platforms will 
have changed time_t to a 64-bit integer, deferring the problem for tens 
of billions of years, by which time POSIX will be in museums, laughed 
at by bored children.  That is, if children still exist.

Joe Gwinn

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