Date-ISO8601
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{
"abstract" : "the three ISO 8601 numerical calendars",
"author" : [
"Andrew Main (Zefram) <zefram@fysh.org>"
],
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"license" : [
"perl_5"
],
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---
abstract: 'the three ISO 8601 numerical calendars'
author:
- 'Andrew Main (Zefram) <zefram@fysh.org>'
build_requires:
Module::Build: '0'
Test::More: '0'
perl: '5.006'
strict: '0'
warnings: '0'
configure_requires:
Module::Build: '0'
NAME
Date::ISO8601 - the three ISO 8601 numerical calendars
DESCRIPTION
The international standard ISO 8601 "Data elements and interchange formats
- Information interchange - Representation of dates and times" defines
three distinct calendars by which days can be labelled. It also defines
textual formats for the representation of dates in these calendars.
This module provides functions to convert dates between these three
calendars and Chronological Julian Day Numbers, which is a suitable
format to do arithmetic with. It also supplies functions that describe
the shape of these calendars, to assist in calendrical calculations.
It also supplies functions to represent dates textually in the ISO
8601 formats. ISO 8601 also covers time of day and time periods, but
this module does nothing relating to those parts of the standard; this
is only about labelling days.
The first ISO 8601 calendar divides time up into years, months, and days.
It corresponds exactly to the Gregorian calendar, invented by Aloysius
Lilius and promulgated by Pope Gregory XIII in the late sixteenth century,
with AD (CE) year numbering. This calendar is applied to all time,
not just to dates after its invention nor just to years 1 and later.
Thus for ancient dates it is the proleptic Gregorian calendar with
astronomical year numbering.
The second ISO 8601 calendar divides time up into the same years as
the first, but divides the year directly into days, with no months.
The standard calls this "ordinal dates". Ordinal dates are commonly
referred to as "Julian dates", a mistake apparently deriving from true
Julian Day Numbers, which divide time up solely into linearly counted
days.
The third ISO 8601 calendar divides time up into years, weeks, and days.
The years approximate the years of the first two calendars, so they stay
in step in the long term, but the boundaries differ. This week-based
calendar is sometimes called "the ISO calendar", apparently in the belief
that ISO 8601 does not define any other. It is also referred to as
"business dates", because it is most used by certain businesses to whom
the week is the most important temporal cycle.
The Chronological Julian Day Number is an integral number labelling each
day, where the day extends from midnight to midnight in whatever time zone
is of interest. It is a linear count of days, where each day's number
is one greater than the previous day's number. It is directly related to
the Julian Date system: in the time zone of the prime meridian, the CJDN
equals the JD at noon. By way of epoch, the day on which the Convention
lib/Date/ISO8601.pm view on Meta::CPAN
=head1 NAME
Date::ISO8601 - the three ISO 8601 numerical calendars
=head1 SYNOPSIS
use Date::ISO8601 qw(present_y);
print present_y($y);
use Date::ISO8601 qw(
month_days cjdn_to_ymd ymd_to_cjdn present_ymd);
lib/Date/ISO8601.pm view on Meta::CPAN
$yw = year_weeks(2000);
($y, $w, $d) = cjdn_to_ywd(2406029);
$cjdn = ywd_to_cjdn(1875, 20, 4);
print present_ywd(2406029);
print present_ywd(1875, 20, 4);
=head1 DESCRIPTION
The international standard ISO 8601 "Data elements and interchange formats
- Information interchange - Representation of dates and times" defines
three distinct calendars by which days can be labelled. It also defines
textual formats for the representation of dates in these calendars.
This module provides functions to convert dates between these three
calendars and Chronological Julian Day Numbers, which is a suitable
format to do arithmetic with. It also supplies functions that describe
the shape of these calendars, to assist in calendrical calculations.
It also supplies functions to represent dates textually in the ISO
8601 formats. ISO 8601 also covers time of day and time periods, but
this module does nothing relating to those parts of the standard; this
is only about labelling days.
The first ISO 8601 calendar divides time up into years, months, and days.
It corresponds exactly to the Gregorian calendar, invented by Aloysius
Lilius and promulgated by Pope Gregory XIII in the late sixteenth century,
with AD (CE) year numbering. This calendar is applied to all time,
not just to dates after its invention nor just to years 1 and later.
Thus for ancient dates it is the proleptic Gregorian calendar with
astronomical year numbering.
The second ISO 8601 calendar divides time up into the same years as
the first, but divides the year directly into days, with no months.
The standard calls this "ordinal dates". Ordinal dates are commonly
referred to as "Julian dates", a mistake apparently deriving from true
Julian Day Numbers, which divide time up solely into linearly counted
days.
The third ISO 8601 calendar divides time up into years, weeks, and days.
The years approximate the years of the first two calendars, so they stay
in step in the long term, but the boundaries differ. This week-based
calendar is sometimes called "the ISO calendar", apparently in the belief
that ISO 8601 does not define any other. It is also referred to as
"business dates", because it is most used by certain businesses to whom
the week is the most important temporal cycle.
The Chronological Julian Day Number is an integral number labelling each
day, where the day extends from midnight to midnight in whatever time zone
is of interest. It is a linear count of days, where each day's number
is one greater than the previous day's number. It is directly related to
the Julian Date system: in the time zone of the prime meridian, the CJDN
equals the JD at noon. By way of epoch, the day on which the Convention
lib/Date/ISO8601.pm view on Meta::CPAN
For years [0, 9999] this is simply four digits. For years outside that
range it is a sign followed by at least four digits.
This is the minimum-length presentation format. If it is desired to
use a form that is longer than necessary, such as to use at least five
digits for all year numbers (as the Long Now Foundation does), then the
right tool is C<sprintf> (see L<perlfunc/sprintf>).
This format is unconditionally conformant to all versions of ISO 8601
for years [1583, 9999]. For years [0, 1582], preceding the historical
introduction of the Gregorian calendar, it is conformant only where
it is mutually agreed that such dates (represented in the proleptic
Gregorian calendar) are acceptable. For years outside the range [0,
9999], where the expanded format must be used, the result is only
conformant to ISO 8601:2004 (earlier versions lacked these formats),
and only where it is mutually agreed to use this format.
=cut
sub present_y($) {
my($y) = @_;
my($sign, $digits) = ("$y" =~ /\A\+?(-?)0*([0-9]+?)\z/);
$digits = ("0" x (4 - length($digits))).$digits
unless length($digits) >= 4;
$sign = "+" if $sign eq "" && length($digits) > 4;
return $sign.$digits;
}
=back
=head2 Gregorian calendar
Each year is divided into twelve months, numbered [1, 12]; month number
1 is January. Each month is divided into days, numbered sequentially
from 1. The month lengths are irregular. The year numbers have
unlimited range.
=over
=item month_days(YEAR, MONTH)
lib/Date/ISO8601.pm view on Meta::CPAN
return sprintf("%s-%02d-%02d", present_y($y),
_numify($m), _numify($d));
}
=back
=head2 Ordinal dates
Each year is divided into days, numbered sequentially from 1. The year
lengths are irregular. The years correspond exactly to those of the
Gregorian calendar.
=over
=item year_days(YEAR)
The parameter identifies a year, and the function returns the number of
days in that year as a native Perl integer.
=cut
lib/Date/ISO8601.pm view on Meta::CPAN
} else {
($y, $d) = @_;
croak "day number $d is out of the displayable range"
unless $d >= 0 && $d < 1000;
}
return sprintf("%s-%03d", present_y($y), _numify($d));
}
=back
=head2 Week-based calendar
Each year is divided into weeks, numbered sequentially from 1. Each week
is divided into seven days, numbered [1, 7]; day number 1 is Monday.
The year lengths are irregular. The year numbers have unlimited range.
The years correspond to those of the Gregorian calendar. Each week is
associated with the Gregorian year that contains its Thursday and hence
contains the majority of its days.
=over
=item year_weeks(YEAR)
The parameter identifies a year, and the function returns the number of
weeks in that year as a native Perl integer.
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