From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=ham autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,7dadb26e573572d
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-12-10 04:27:26 PST
Path: 
 archiver1.google.com!news2.google.com!newsfeed2.dallas1.level3.net!news.level3.com!news-out.visi.com!petbe.visi.com!skynet.be!news.mailgate.org!news-zh.switch.ch!switch.ch!newsfeed-zh.ip-plus.net!news.ip-plus.net!not-for-mail
From: Thomas Wolf <t_wolf@angelfire.com>
Newsgroups: comp.lang.ada
Subject: Re: ada calendar
Date: Wed, 10 Dec 2003 13:27:24 +0100
Organization: ---
Message-ID: <MPG.1a412f88b61dac9c989681@news.ip-plus.ch>
References: <br1ag1$frn$1@dolly.uninett.no>
 <H%eBb.344362$275.1139897@attbi_s53>
 <br4ri5$28ukqo$1@ID-25716.news.uni-berlin.de>
 <NOWdnT6JV8DAS0uiRVn-iw@comcast.com>
NNTP-Posting-Host: paraguard.paranor.ch
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-15"
Content-Transfer-Encoding: 7bit
X-Trace: rex.ip-plus.net 1071059323 28067 193.246.248.114 (10 Dec 2003
 12:28:43 GMT)
X-Complaints-To: abuse@ip-plus.net
NNTP-Posting-Date: Wed, 10 Dec 2003 12:28:43 +0000 (UTC)
X-Newsreader: MicroPlanet Gravity v2.60
Xref: archiver1.google.com comp.lang.ada:3305
Date: 2003-12-10T13:27:24+01:00
List-Id: <comp.lang.ada>

rieachus@comcast.net wrote:
> The latest version of the proposed additions for Ada 0Y can be found at:
> http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00351.TXT?rev=1.2>

I see that this proposal includes some functionality for dealing with
leap seconds. It proposes (among other things)

procedure Difference (Left, Right : Time;
                      Days : out Day_Count;
                      Seconds : out Duration;
		      Leap_Seconds : out Leap_Seconds_Count);
    Returns the difference between Left and Right.
    Days is the number of days of difference, Seconds is the
    remainder seconds of difference, and Leap_Seconds is the number
    of leap seconds.
    If Left < Right, then Seconds <= 0.0, Days <= 0, and
    Leap_Seconds <= 0.
    Otherwise, all values are non-negative.

How is this supposed to work if Left or both Left and Right are in
the future? You cannot predict when the next leap second will be
inserted -- it depends on the irregularities of Earth's rotation,
and IERS inserts a leap second whenever necessary (well, at the end
of June or December) to keep the difference between UT1 und UTC <
0.9 sec.

Also implementing this for past dates needs a look-up table.

So, what is the number of leap seconds between 2004-01-01, 00:00:00
and 2105-01-01 00:00:00? Executing the proposed subprogram now would
probably return Leap_Seconds = 0, but executing it in 20 years, it
would probably have to return a non-zero value. (Because by then,
IERS will most probably have inserted at least one additional leap
second.)

-- 
-----------------------------------------------------------------
Thomas Wolf                          e-mail: t_wolf@angelfire.com