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From: brian.b.mcguinness@lmco.com
Newsgroups: comp.lang.ada
Subject: Re: Advice on Calendar.Time
Date: 9 Nov 2005 11:37:44 -0800
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Date: 2005-11-09T11:37:44-08:00
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So one approach would be to use Ada.Calendar.Time_Zones as Martin
suggested, e.g. get
the time of day from Clock, using Split to divide it into year, month,
day, and second, then get the time offset (in minutes) from
UTC_Time_Offset, and convert to GMT accordingly.  But the question
remains of how to deal with leap seconds.  (And why does
UTC_Time_Offset return a value in minutes rather than seconds, which
would make it more compatible with Split?)

Astronomers face a similar problem in converting conventional dates and
times to the Julian day number, the number of days since 00:00 GMT on
January 1, 4713 B.C.  They have software to keep track of leap seconds
and so on.  So you might find something useful in a package of
astronomical subroutines such as SOFA, which is at
http://www.iau-sofa.rl.ac.uk/
(this is in Fortran, not Ada, but it could probably be translated
without too much trouble or Fortran routines might be linked into an
Ada program).

Good luck.

--- Brian