It seems like it depends which direction you are trying to convert.
TAI to UTC does require knowledge of both the the current (TAI-UTC)
and that a leap second is in progress.
As long as we only have positive leap seconds you can get away with
applying the new value of (TAI-UTC) after the leap second.
To go from UTC to TAI, down in the code will be an hhmmss_to_sssss
function. If this is the simple minded one-line function that
immediately comes to mind then it will have no difficulty handling
the non-normalized 23:59:60 and putting it 86401 seconds after
00:00:00 earlier that day. So here you can apply the new value of
(TAI-UTC) starting with the first second after the leap second.
And then, in the case of a negative leapsecond you frantically scramble
to fix your code.
Richard Clark
On Tue, 31 Jan 2017, Warner Losh wrote:
On Tue, Jan 31, 2017 at 12:08 PM, Steve Allen <[email protected]> wrote:
On Tue 2017-01-31T13:58:15 -0500, Brooks Harris hath writ:
Ah, so who's right?
I prefer to think of a leap second as being truly intercalary.
It is saying to atomic clock "It's not tomorrow yet, wait a second."
It is between one calendar day of UTC and the next calendar day of UTC.
It belongs to neither of them. The tag 2016-12-31T23:59:60 is merely
a way of indicating which two days it is between.
It is unfortunate that nobody thought this stuff through in 1969 when
the decision was made to implement the leap second, and no matter how
it is expressed, encoded, and calculated it will be a special case.
Philosophically you may be right.
Mathematically, however, I don't think that makes much sense. :60 is
an irregular radix. It's clearly added to the prior day, just like Feb
29th is part of February. Also, doing the long-hand math on the
irregular radix, it also makes sense to have it be part of the prior
day and to increment the offset at the start of the leap second.
Warner
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