[LEAPSECS] Leap seconds ain't broken, but most implementations are broken

[Zefram]

Brooks Harris wrote:
>That would indeed be a smart computer. If it can divine the next Leap Second
>without need to consult an external source,

To be clear: obviously knowledge of the upcoming leap second must come
from some external source.  A system with such advance knowledge is then
able to apply that knowledge at the proper time, maintaining a correct
clock through the leap second, without any further external contact.
It doesn't have to be told that the leap second has arrived.  This kind
of knowledge is exhibited by some Unices, but not by Windows.

>I meant dealing with the mismatch between UTC with Leap seconds and
>86400-second-day systems, which (pure) Gregorian and POSIX, are.

No, the Gregorian calendar is yet another thing that doesn't imply
86400-second days.  (POSIX time_t is another.)  There's a general pattern
here that whenever there's some construct that counts or labels days,
and is (as most are) silent on the fine internal structure of those days,
you (Brooks) interpret it as specifying that the days consist of exactly
86400 SI seconds.  (Or atomically-realised seconds, which you do not
distinguish from SI seconds.)  I cannot think of an occasion when you
have drawn that inference and been correct.

-zefram