package Time::JulianDay;
require 5.000;
use Carp;
use Time::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 = 2011.0505;
# 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 $jds - tz_local_offset($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 $jds - tz_local_offset($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 with help from
previous work by
Kurt Jaeger aka PI
based on postings from: Ian Miller ;
Gary Puckering
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 cpan@dave.sharnoff.org.