[LEAPSECS] presentations from AAS Future of Time sessions

[Brooks Harris]

On 2014-01-18 08:53 AM, Warner Losh wrote:

> On Jan 18, 2014, at 6:31 AM, Magnus Danielson wrote:

>

>> On 18/01/14 11:56, Poul-Henning Kamp wrote:

>>> In message <52DA2A0F.9060704 at rubidium.dyndns.org>, Magnus Danielson writes:

>>>

>>>> If you where right about not basing it on the orbital debris, then we

>>>> should not attempt to be using concepts like seconds, minutes, hours,

>>>> days, weeks, months, years [...]

>>> As you are no doubt aware, the POSIX time_t does not do that.

>> The POSIX time_t still tries to encode it, using some of the rules that makes of UTC, including SI-seconds. However, the argument was not about POSIX time_t, but about what "Universal" in UTC actually means.

> POSIX time_t is explicitly not UTC.


Ah, well, it is explicitly UTC, but not the UTC we'd like.

section 3.150 Epoch says - "The time zero hours, zero minutes, zero 
seconds, on January 1, 1970 Coordinated Universal Time (UTC)."

But its described behavior is not *modern* UTC (with Leap Seconds), and 
this is made clearer by section A.4.15 Seconds Since the Epoch -

"Coordinated Universal Time (UTC) includes leap seconds. However, in 
POSIX time (seconds
since the Epoch), leap seconds are ignored (not applied) to provide an 
easy and compatible
method of computing time differences. Broken-down POSIX time is 
therefore not necessarily
UTC, despite its appearance."

"Broken-down POSIX time" is a YY-MM-DD hh:mm:ss representation - a 
*calendar* date-time.

POSIX behaves as an *uncompensated-for-Leap-Seconds* Gregorian calendar 
counting scheme.


-Brooks


>

> Warner

>

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