leap seconds and the stdc library Post: 94270

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Top Forums UNIX for Advanced & Expert Users leap seconds and the stdc library Post 94270 by Perderabo on Wednesday 28th of December 2005 03:09:56 PM

12-28-2005

Administrator Emeritus

No record of leap seconds is kept. So each time a leap second occurs, calculation of past timestamps becomes wrong by one more second. In the unix view of time, there are no leap seconds. Instead of a leap second, an occasional second is twice as long as other seconds. But this means that you can precalculate, for example, the number of seconds in a year. A system that adheres strictly to the leap second paradigm cannot do that since leap seconds cannot be predicted by more than 6 months. Posix discussed leap seconds at length and decided on this approach. The deciding factor was the need to precalculate future timestamps. Another consideration was that non-networked unix systems may not have access to a leap second knowledgable clock.

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datetime::leapsecond

DateTime::LeapSecond(3) 				User Contributed Perl Documentation				   DateTime::LeapSecond(3)

NAME

       DateTime::LeapSecond - leap seconds table and utilities

VERSION

       version 0.77

SYNOPSIS

	 use DateTime;
	 use DateTime::LeapSecond;

	 print "Leap seconds between years 1990 and 2000 are ";
	 print DateTime::Leapsecond::leap_seconds( $utc_rd_2000 ) -
	       DateTime::Leapsecond::leap_seconds( $utc_rd_1990 );

DESCRIPTION

       This module is used to calculate leap seconds for a given Rata Die day. It is used when DateTime.pm cannot compile the XS version of this
       code.

       This library is known to be accurate for dates until December 2009.

       There are no leap seconds before 1972, because that's the year this system was implemented.

       o   leap_seconds( $rd )

	   Returns the number of accumulated leap seconds for a given day, in the range 0 .. 22.

       o   extra_seconds( $rd )

	   Returns the number of leap seconds for a given day, in the range -2 .. 2.

       o   day_length( $rd )

	   Returns the number of seconds for a given day, in the range 86398 .. 86402.

SEE ALSO

       <http://hpiers.obspm.fr/eop-pc/earthor/utc/leapsecond.html>

       http://datetime.perl.org

AUTHOR

       Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE

       This software is Copyright (c) 2012 by Dave Rolsky.

       This is free software, licensed under:

	 The Artistic License 2.0 (GPL Compatible)

perl v5.16.2							    2013-08-25						   DateTime::LeapSecond(3)