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*Wed Apr 29 19:54:35 2009 UTC*
(10 years, 9 months ago)
by *chenry*

Branch:**MAIN**

CVS Tags:**rast_rel_2009_05_18, rast_rel_2009_0925, rast_rel_2010_0827, rast_rel_2009_07_09, rast_rel_2010_0928, rast_rel_2010_0526, rast_rel_2010_1206, rast_rel_2010_0118**

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package Time::JulianDay; require 5.000; use Carp; use TimeZone; @ISA = qw(Exporter); @EXPORT = qw(julian_day inverse_julian_day day_of_week jd_secondsgm jd_secondslocal jd_timegm jd_timelocal gm_julian_day local_julian_day ); @EXPORT_OK = qw($brit_jd); use strict; use integer; # constants use vars qw($brit_jd $jd_epoch $jd_epoch_remainder $VERSION); $VERSION = 2003.1125; # calculate the julian day, given $year, $month and $day sub julian_day { my($year, $month, $day) = @_; my($tmp); use Carp; # confess() unless defined $day; $tmp = $day - 32075 + 1461 * ( $year + 4800 - ( 14 - $month ) / 12 )/4 + 367 * ( $month - 2 + ( ( 14 - $month ) / 12 ) * 12 ) / 12 - 3 * ( ( $year + 4900 - ( 14 - $month ) / 12 ) / 100 ) / 4 ; return($tmp); } sub gm_julian_day { my($secs) = @_; my($sec, $min, $hour, $mon, $year, $day, $month); ($sec, $min, $hour, $day, $mon, $year) = gmtime($secs); $month = $mon + 1; $year += 1900; return julian_day($year, $month, $day) } sub local_julian_day { my($secs) = @_; my($sec, $min, $hour, $mon, $year, $day, $month); ($sec, $min, $hour, $day, $mon, $year) = localtime($secs); $month = $mon + 1; $year += 1900; return julian_day($year, $month, $day) } sub day_of_week { my ($jd) = @_; return (($jd + 1) % 7); # calculate weekday (0=Sun,6=Sat) } # The following defines the first day that the Gregorian calendar was used # in the British Empire (Sep 14, 1752). The previous day was Sep 2, 1752 # by the Julian Calendar. The year began at March 25th before this date. $brit_jd = 2361222; # Usage: ($year,$month,$day) = &inverse_julian_day($julian_day) sub inverse_julian_day { my($jd) = @_; my($jdate_tmp); my($m,$d,$y); carp("warning: julian date $jd pre-dates British use of Gregorian calendar\n") if ($jd < $brit_jd); $jdate_tmp = $jd - 1721119; $y = (4 * $jdate_tmp - 1)/146097; $jdate_tmp = 4 * $jdate_tmp - 1 - 146097 * $y; $d = $jdate_tmp/4; $jdate_tmp = (4 * $d + 3)/1461; $d = 4 * $d + 3 - 1461 * $jdate_tmp; $d = ($d + 4)/4; $m = (5 * $d - 3)/153; $d = 5 * $d - 3 - 153 * $m; $d = ($d + 5) / 5; $y = 100 * $y + $jdate_tmp; if($m < 10) { $m += 3; } else { $m -= 9; ++$y; } return ($y, $m, $d); } { my($sec, $min, $hour, $day, $mon, $year) = gmtime(0); $year += 1900; if ($year == 1970 && $mon == 0 && $day == 1) { # standard unix time format $jd_epoch = 2440588; } else { $jd_epoch = julian_day($year, $mon+1, $day); } $jd_epoch_remainder = $hour*3600 + $min*60 + $sec; } sub jd_secondsgm { my($jd, $hr, $min, $sec) = @_; my($r) = (($jd - $jd_epoch) * 86400 + $hr * 3600 + $min * 60 - $jd_epoch_remainder); no integer; return ($r + $sec); use integer; } sub jd_secondslocal { my($jd, $hr, $min, $sec) = @_; my $jds = jd_secondsgm($jd, $hr, $min, $sec); return $jds - Time::Timezone::tz_local_offset($jds); } # this uses a 0-11 month to correctly reverse localtime() sub jd_timelocal { my ($sec,$min,$hours,$mday,$mon,$year) = @_; $year += 1900 unless $year > 1000; my $jd = julian_day($year, $mon+1, $mday); my $jds = jd_secondsgm($jd, $hours, $min, $sec); return $jds - Time::Timezone::tz_local_offset($jds); } # this uses a 0-11 month to correctly reverse gmtime() sub jd_timegm { my ($sec,$min,$hours,$mday,$mon,$year) = @_; $year += 1900 unless $year > 1000; my $jd = julian_day($year, $mon+1, $mday); return jd_secondsgm($jd, $hours, $min, $sec); } 1; __END__ =head1 NAME Time::JulianDay -- Julian calendar manipulations =head1 SYNOPSIS use Time::JulianDay $jd = julian_day($year, $month_1_to_12, $day) $jd = local_julian_day($seconds_since_1970); $jd = gm_julian_day($seconds_since_1970); ($year, $month_1_to_12, $day) = inverse_julian_day($jd) $dow = day_of_week($jd) print (Sun,Mon,Tue,Wed,Thu,Fri,Sat)[$dow]; $seconds_since_jan_1_1970 = jd_secondslocal($jd, $hour, $min, $sec) $seconds_since_jan_1_1970 = jd_secondsgm($jd, $hour, $min, $sec) $seconds_since_jan_1_1970 = jd_timelocal($sec,$min,$hours,$mday,$month_0_to_11,$year) $seconds_since_jan_1_1970 = jd_timegm($sec,$min,$hours,$mday,$month_0_to_11,$year) =head1 DESCRIPTION JulianDay is a package that manipulates dates as number of days since some time a long time ago. It's easy to add and subtract time using julian days... The day_of_week returned by day_of_week() is 0 for Sunday, and 6 for Saturday and everything else is in between. =head1 ERRATA Time::JulianDay is not a correct implementation. There are two problems. The first problem is that Time::JulianDay only works with integers. Julian Day can be fractional to represent time within a day. If you call inverse_julian_day() with a non-integer time, it will often give you an incorrect result. The second problem is that Julian Days start at noon rather than midnight. The julian_day() function returns results that are too large by 0.5. What to do about these problems is currently open for debate. I'm tempted to leave the current functions alone and add a second set with more accurate behavior. There is another implementation in Astro::Time that may be more accurate. =head1 GENESIS Written by David Muir Sharnoff <muir@idiom.com> with help from previous work by Kurt Jaeger aka PI <zrzr0111@helpdesk.rus.uni-stuttgart.de> based on postings from: Ian Miller <ian_m@cix.compulink.co.uk>; Gary Puckering <garyp%cognos.uucp@uunet.uu.net> based on Collected Algorithms of the ACM ?; and the unknown-to-me author of Time::Local. =head1 LICENSE Copyright (C) 1996-1999 David Muir Sharnoff. License hereby granted for anyone to use, modify or redistribute this module at their own risk. Please feed useful changes back to muir@idiom.com.

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