[LEAPSECS] Time math libraries, UTC to TAI

[Michael.Deckers.]

   On 2017-01-02 18:55, Brooks Harris wrote about the correspondence

       | Date        | MJD        | NTP | NTP Timestamp | Epoch            |
       | 4 Oct 1582  | -100,851   | -3  | 2,873,647,488 | Last day 
Julian  |


> Ah, I think the table is correct - that's the infamous reset made by 
> the Gregorian calendar  to correct accumulated inaccuracies in the 
> Julian and also, I believe, counted days at midnight, not noon, as 
> Julian did (does).

    Sure, the Julian date of the day before the day with Gregorian date 
1582-10-25
    is 1582 Oct 04 -- but the epoch given in the table with the MJD 
value and the
    NTP timestamp values is obviously 10 days earlier: they all indicate 
Julian date
    1582 Sep 24 and Gregorian date 1582-10-04, as I have noted earlier.

    The table indicates the (not usual) confusion about "omitted days" where
    it is unclear which numbers should be decreased (or increased) by ten.
    I do not want to be sarcastic but my managers would refuse to buy 
software
    when the spec (already) contains such blunders.

    And dates in the Julian calendar are taken to begin at midnight, as 
in the
    Gregorian calendar. It is the Julian day numbers used in astronomy that
    take integral values at noon epochs -- but they have nothing to do with
    the Julian calendar, except perhaps for the origin of the name.

    Michael Deckers.