=head1 NAME

Date::JD - conversion between flavours of Julian Date

=head1 SYNOPSIS

    use Date::JD qw(jd_to_mjd mjd_to_cjdnf cjdn_to_rd);

    $mjd = jd_to_mjd($jd);
    ($cjdn, $cjdf) = mjd_to_cjdnf($mjd, $tz);
    $rd = cjdn_to_rd($cjdn, $cjdf);

    # and 509 other conversion functions

=head1 DESCRIPTION

For date and time calculations it is convenient to represent dates by
a simple linear count of days, rather than in a particular calendar.
This is such a good idea that it has been invented several times.
If there were a single such linear count then it would be the obvious
data interchange format between calendar modules.  With several
versions, calendar modules can use such sensible data formats and still
have interoperability problems.  This module tackles that problem,
by performing conversions between different flavours of day count.
These day count systems are generically known as "Julian Dates", after
the most venerable of them.

Among Julian Date systems there are also some non-trivial differences
of concept.  There are systems that count only complete days, and
those that count fractional days also.  There are some that are fixed
to Universal Time (time on the prime meridian), and others that are
interpreted according to a timezone.  Some consider the day to start at
noon and others at midnight, which is semantically significant for the
complete-day counts.  The functions of this module appropriately handle
the semantics of all the non-trivial conversions.

The day count systems supported by this module are Julian Date, Reduced
Julian Date, Modified Julian Date, Dublin Julian Date, Truncated Julian
Date, Chronological Julian Date, Rata Die, and Lilian Date, each in both
integral and fractional forms.

=head2 Flavours of day count

In the interests of orthogonality, all flavours of day count come in both
integral and fractional varieties.  Generally, there is a quantity named
"XYZD" ("XYZ Date") which is a real count of days since a particular epoch
(an integer plus a fraction) and a corresponding quantity named "XYZDN"
("XYZ Day Number") which is a count of complete days since the same epoch.
XYZDN is the integral part of XYZD.  There is also a quantity named
"XYZDF" ("XYZ Day Fraction") which is a count of fractional days since
the XYZDN changed (whether that is noon or midnight).  XYZDF is the
fractional part of XYZD, in the range [0, 1).

This quantity naming pattern is derived from JD (Julian Date) and JDN
(Julian Day Number) which have the described correspondence.  Most of
the other flavours of day count listed below conventionally come in only
one of the two varieties.  The "XYZDF" name type is a neologism.

All calendar dates given are in ISO 8601 form (Gregorian calendar with
astronomical year numbering).  An hour number is appended to each date,
separated by a "T"; hour 00 is midnight at the start of the day and hour
12 is noon in the middle of the day.  An appended "Z" indicates that the
date is to be interpreted in Universal Time (the timezone of the prime
meridian), and so is absolute; where any other timezone is to be used
then this is explicitly noted.

=over

=item JD (Julian Date)

days elapsed since -4713-11-24T12Z.  This epoch is the most recent
coincidence of the first year of the Metonic cycle, indiction cycle, and
day-of-week cycle, using the Julian calendar.  It was correspondingly
named after the Julian calendar, and thus after Julius Caesar.  Some
information can be found at L<http://en.wikipedia.org/wiki/Julian_day>.

=item RJD (Reduced Julian Date)

days elapsed since 1858-11-16T12Z (JD 2400000.0).  Rarely used.

=item MJD (Modified Julian Date)

days elapsed since 1858-11-17T00Z (JD 2400000.5).  This was introduced by
the Smithsonian Astrophysical Observatory in 1957, and is recommended for
general use by the International Astronomical Union and other authorities.

=item DJD (Dublin Julian Date)

days elapsed since 1899-12-31T12Z (JD 2415020.0).  This was invented by
the International Astronomical Union, and the epoch in Terrestrial Time
is the J1900.0 epoch used in astronomy.  (Note: not B1900.0, which is
a few hours later.)  It is rarely used.

=item TJD (Truncated Julian Date)

days elapsed since 1968-05-24T00Z (JD 2440000.5).  This is primarily
used by NASA, who devised it during the Apollo era.  There is a
rumour that it's defined cyclically, as (JD - 0.5) mod 10000, but see
L<http://cossc.gsfc.nasa.gov/cossc/batse/hilev/TJD.TABLE>.

=item CJD (Chronological Julian Date)

days elapsed since -4713-11-24T00 in the timezone of interest.
CJD = JD + 0.5 + Zoff, where Zoff is the timezone offset in
fractional days.  This was devised by Peter Meyer, and described in
L<http://www.hermetic.ch/cal_stud/cjd.htm>.

=item RD (Rata Die)

days elapsed since 0000-12-31T00 in the timezone of interest (CJD
1721425.0).  This is defined in the book Calendrical Calculations.
Confusingly, in the book the integral form is also called "RD".
The integral form is called "RDN" by this module to avoid confusion,
reserving the name "RD" for the fractional form.  (The book is best
treated with caution due to the embarrassingly large number of errors
and instances of muddled thinking.)

=item LD (Lilian Date)

days elapsed since 1582-10-14T00 in the timezone of interest (CJD
2299160.0).  This epoch is the day before the day that the Gregorian
calendar first went into use.  It is named after Aloysius Lilius, the
inventor of the Gregorian calendar.

=back

The interesting differences between these flavours are whether the
day starts at noon or at midnight, and whether they are absolute or
timezone-relative.  Three of the four combinations of these features
exist.  There is no convention for counting days from timezone-relative
noon that the author of this module is aware of.

For more background on these day count systems,
L<http://en.wikipedia.org/wiki/Julian_Date> is a good starting place.

=head2 Meaning of the day

A day count has meaning only in the context of a particular definition
of "day".  There are two main flavours of day to consider: solar and
conventional.

A solar day is based on the apparent motion of Sol in the Terran sky (and
thus on the rotation and orbit of Terra).  The rotation of Terra is not
constant in time, so this type of day is really a measure of angle, not
of time.  This is how days have been counted since antiquity, and is still
(as of 2006) the basis of civil time.  There are two subtypes of solar
day: apparent and mean.  The apparent solar day is based on the actual
observable position of Sol in the sky from day to day, whereas the mean
solar day smooths this motion out, in time, over the course of the year.
At the sub-second level there are different types of smoothing that can
be used (UT1, UT2, et al).

A conventional day is any type of day that is not based on Terran
rotation.  The astronomical Ephemeris Time, a time scale based on the
motion of bodies in the Solar system, has a time unit that it calls
"day" which is derived from astronomical observations.  The modern
relativistic coordinate time scales such as TT have a notional "day"
of exactly 86400 SI seconds.  The atomic time scale TAI also has a "day"
which is as close to 86400 SI seconds as can be achieved.  All of these
"days" are roughly the duration of one Sol-relative rotation of Terra
during the early nineteenth century, but are not otherwise related to
planetary rotation.

Each of the day count scales handled by this module can be used with any
of these types of day.  For a day number to be meaningful it is necessary
to be aware of which kind of day it is counting.  Conversion between the
different types of day is out of scope for this module.  (See L<Time::UTC>
for TAI/UTC conversion.)

=cut

package Date::JD;

{ use 5.006; }
use warnings;
use strict;

use Carp qw(croak);

our $VERSION = "0.006";

use parent "Exporter";
our @EXPORT_OK;

my %jd_flavours = (
	jd => { epoch_jd => 0 },
	rjd => { epoch_jd => 2400000.0 },
	mjd => { epoch_jd => 2400000.5 },
	djd => { epoch_jd => 2415020.0 },
	tjd => { epoch_jd => 2440000.5 },
	cjd => { epoch_jd => -0.5, zone => 1 },
	rd => { epoch_jd => 1721424.5, zone => 1 },
	ld => { epoch_jd => 2299159.5, zone => 1 },
);

=head1 FUNCTIONS

Day counts in this API may be native Perl numbers or C<Math::BigRat>
objects.  Both are acceptable for all parameters, in any combination.
In all conversion functions, the result is of the same type as the
input, provided that the inputs are of consistent type.  If native Perl
numbers are supplied then the conversion is subject to floating point
rounding, and possible overflow if the numbers are extremely large.
The use of C<Math::BigRat> is recommended to avoid these problems.
With C<Math::BigRat> the results are exact.

There are conversion functions between all pairs of day count systems.
This is a total of 512 conversion functions (including 32 identity
functions).

When converting between timezone-relative counts (CJD, RD, LD) and
absolute counts (JD, RJD, MJD, DJD, TJD), the timezone that is being used must
be specified.  It is given in a ZONE argument as a fractional number of
days offset from Universal Time.  For example, US Central Standard Time,
6 hours behind UT, would be specified as a ZONE argument of -0.25.
Beware of floating point rounding when the offset does not have a
terminating binary representation (e.g., US Eastern Standard Time at
-5/24); use of C<Math::BigRat> avoids this problem.  A ZONE parameter is
not used when converting between absolute day counts (e.g., between JD
and MJD) or between timezone-relative counts (e.g., between CJD and LD).

=over

=item jd_to_jd(JD)

=item jd_to_rjd(JD)

=item jd_to_mjd(JD)

=item jd_to_djd(JD)

=item jd_to_tjd(JD)

=item jd_to_cjd(JD, ZONE)

=item jd_to_rd(JD, ZONE)

=item jd_to_ld(JD, ZONE)

=item rjd_to_jd(RJD)

=item rjd_to_rjd(RJD)

=item rjd_to_mjd(RJD)

=item rjd_to_djd(RJD)

=item rjd_to_tjd(RJD)

=item rjd_to_cjd(RJD, ZONE)

=item rjd_to_rd(RJD, ZONE)

=item rjd_to_ld(RJD, ZONE)

=item mjd_to_jd(MJD)

=item mjd_to_rjd(MJD)

=item mjd_to_mjd(MJD)

=item mjd_to_djd(MJD)

=item mjd_to_tjd(MJD)

=item mjd_to_cjd(MJD, ZONE)

=item mjd_to_rd(MJD, ZONE)

=item mjd_to_ld(MJD, ZONE)

=item djd_to_jd(DJD)

=item djd_to_rjd(DJD)

=item djd_to_mjd(DJD)

=item djd_to_djd(DJD)

=item djd_to_tjd(DJD)

=item djd_to_cjd(DJD, ZONE)

=item djd_to_rd(DJD, ZONE)

=item djd_to_ld(DJD, ZONE)

=item tjd_to_jd(TJD)

=item tjd_to_rjd(TJD)

=item tjd_to_mjd(TJD)

=item tjd_to_djd(TJD)

=item tjd_to_tjd(TJD)

=item tjd_to_cjd(TJD, ZONE)

=item tjd_to_rd(TJD, ZONE)

=item tjd_to_ld(TJD, ZONE)

=item cjd_to_jd(CJD, ZONE)

=item cjd_to_rjd(CJD, ZONE)

=item cjd_to_mjd(CJD, ZONE)

=item cjd_to_djd(CJD, ZONE)

=item cjd_to_tjd(CJD, ZONE)

=item cjd_to_cjd(CJD)

=item cjd_to_rd(CJD)

=item cjd_to_ld(CJD)

=item rd_to_jd(RD, ZONE)

=item rd_to_rjd(RD, ZONE)

=item rd_to_mjd(RD, ZONE)

=item rd_to_djd(RD, ZONE)

=item rd_to_tjd(RD, ZONE)

=item rd_to_cjd(RD)

=item rd_to_rd(RD)

=item rd_to_ld(RD)

=item ld_to_jd(LD, ZONE)

=item ld_to_rjd(LD, ZONE)

=item ld_to_mjd(LD, ZONE)

=item ld_to_djd(LD, ZONE)

=item ld_to_tjd(LD, ZONE)

=item ld_to_cjd(LD)

=item ld_to_rd(LD)

=item ld_to_ld(LD)

These functions convert from one continuous day count to another.
This principally involve a change of epoch.  The input identifies a
point in time, as a continuous day count of input flavour.  The function
returns the same point in time, represented as a continuous day count
of output flavour.

=item jd_to_jdnn(JD)

=item jd_to_rjdnn(JD)

=item jd_to_mjdnn(JD)

=item jd_to_djdnn(JD)

=item jd_to_tjdnn(JD)

=item jd_to_cjdnn(JD, ZONE)

=item jd_to_rdnn(JD, ZONE)

=item jd_to_ldnn(JD, ZONE)

=item rjd_to_jdnn(RJD)

=item rjd_to_rjdnn(RJD)

=item rjd_to_mjdnn(RJD)

=item rjd_to_djdnn(RJD)

=item rjd_to_tjdnn(RJD)

=item rjd_to_cjdnn(RJD, ZONE)

=item rjd_to_rdnn(RJD, ZONE)

=item rjd_to_ldnn(RJD, ZONE)

=item mjd_to_jdnn(MJD)

=item mjd_to_rjdnn(MJD)

=item mjd_to_mjdnn(MJD)

=item mjd_to_djdnn(MJD)

=item mjd_to_tjdnn(MJD)

=item mjd_to_cjdnn(MJD, ZONE)

=item mjd_to_rdnn(MJD, ZONE)

=item mjd_to_ldnn(MJD, ZONE)

=item djd_to_jdnn(DJD)

=item djd_to_rjdnn(DJD)

=item djd_to_mjdnn(DJD)

=item djd_to_djdnn(DJD)

=item djd_to_tjdnn(DJD)

=item djd_to_cjdnn(DJD, ZONE)

=item djd_to_rdnn(DJD, ZONE)

=item djd_to_ldnn(DJD, ZONE)

=item tjd_to_jdnn(TJD)

=item tjd_to_rjdnn(TJD)

=item tjd_to_mjdnn(TJD)

=item tjd_to_djdnn(TJD)

=item tjd_to_tjdnn(TJD)

=item tjd_to_cjdnn(TJD, ZONE)

=item tjd_to_rdnn(TJD, ZONE)

=item tjd_to_ldnn(TJD, ZONE)

=item cjd_to_jdnn(CJD, ZONE)

=item cjd_to_rjdnn(CJD, ZONE)

=item cjd_to_mjdnn(CJD, ZONE)

=item cjd_to_djdnn(CJD, ZONE)

=item cjd_to_tjdnn(CJD, ZONE)

=item cjd_to_cjdnn(CJD)

=item cjd_to_rdnn(CJD)

=item cjd_to_ldnn(CJD)

=item rd_to_jdnn(RD, ZONE)

=item rd_to_rjdnn(RD, ZONE)

=item rd_to_mjdnn(RD, ZONE)

=item rd_to_djdnn(RD, ZONE)

=item rd_to_tjdnn(RD, ZONE)

=item rd_to_cjdnn(RD)

=item rd_to_rdnn(RD)

=item rd_to_ldnn(RD)

=item ld_to_jdnn(LD, ZONE)

=item ld_to_rjdnn(LD, ZONE)

=item ld_to_mjdnn(LD, ZONE)

=item ld_to_djdnn(LD, ZONE)

=item ld_to_tjdnn(LD, ZONE)

=item ld_to_cjdnn(LD)

=item ld_to_rdnn(LD)

=item ld_to_ldnn(LD)

These functions convert from a continuous day count to an integral day
count.  The input identifies a point in time, as a continuous day count
of input flavour.  The function returns the day number of output flavour
that applies at that instant.  The process throws away information about
the time of (output-flavour) day.

=item jd_to_jdnf(JD)

=item jd_to_rjdnf(JD)

=item jd_to_mjdnf(JD)

=item jd_to_djdnf(JD)

=item jd_to_tjdnf(JD)

=item jd_to_cjdnf(JD, ZONE)

=item jd_to_rdnf(JD, ZONE)

=item jd_to_ldnf(JD, ZONE)

=item rjd_to_jdnf(RJD)

=item rjd_to_rjdnf(RJD)

=item rjd_to_mjdnf(RJD)

=item rjd_to_djdnf(RJD)

=item rjd_to_tjdnf(RJD)

=item rjd_to_cjdnf(RJD, ZONE)

=item rjd_to_rdnf(RJD, ZONE)

=item rjd_to_ldnf(RJD, ZONE)

=item mjd_to_jdnf(MJD)

=item mjd_to_rjdnf(MJD)

=item mjd_to_mjdnf(MJD)

=item mjd_to_djdnf(MJD)

=item mjd_to_tjdnf(MJD)

=item mjd_to_cjdnf(MJD, ZONE)

=item mjd_to_rdnf(MJD, ZONE)

=item mjd_to_ldnf(MJD, ZONE)

=item djd_to_jdnf(DJD)

=item djd_to_rjdnf(DJD)

=item djd_to_mjdnf(DJD)

=item djd_to_djdnf(DJD)

=item djd_to_tjdnf(DJD)

=item djd_to_cjdnf(DJD, ZONE)

=item djd_to_rdnf(DJD, ZONE)

=item djd_to_ldnf(DJD, ZONE)

=item tjd_to_jdnf(TJD)

=item tjd_to_rjdnf(TJD)

=item tjd_to_mjdnf(TJD)

=item tjd_to_djdnf(TJD)

=item tjd_to_tjdnf(TJD)

=item tjd_to_cjdnf(TJD, ZONE)

=item tjd_to_rdnf(TJD, ZONE)

=item tjd_to_ldnf(TJD, ZONE)

=item cjd_to_jdnf(CJD, ZONE)

=item cjd_to_rjdnf(CJD, ZONE)

=item cjd_to_mjdnf(CJD, ZONE)

=item cjd_to_djdnf(CJD, ZONE)

=item cjd_to_tjdnf(CJD, ZONE)

=item cjd_to_cjdnf(CJD)

=item cjd_to_rdnf(CJD)

=item cjd_to_ldnf(CJD)

=item rd_to_jdnf(RD, ZONE)

=item rd_to_rjdnf(RD, ZONE)

=item rd_to_mjdnf(RD, ZONE)

=item rd_to_djdnf(RD, ZONE)

=item rd_to_tjdnf(RD, ZONE)

=item rd_to_cjdnf(RD)

=item rd_to_rdnf(RD)

=item rd_to_ldnf(RD)

=item ld_to_jdnf(LD, ZONE)

=item ld_to_rjdnf(LD, ZONE)

=item ld_to_mjdnf(LD, ZONE)

=item ld_to_djdnf(LD, ZONE)

=item ld_to_tjdnf(LD, ZONE)

=item ld_to_cjdnf(LD)

=item ld_to_rdnf(LD)

=item ld_to_ldnf(LD)

These functions convert from a continuous day count to an integral day
count with separate fraction.  The input identifies a point in time,
as a continuous day count of input flavour.  The function returns a
list of two items: the day number and fractional day of output flavour,
which together identify the same point in time as the input.

=item jd_to_jdn(JD)

=item jd_to_rjdn(JD)

=item jd_to_mjdn(JD)

=item jd_to_djdn(JD)

=item jd_to_tjdn(JD)

=item jd_to_cjdn(JD, ZONE)

=item jd_to_rdn(JD, ZONE)

=item jd_to_ldn(JD, ZONE)

=item rjd_to_jdn(RJD)

=item rjd_to_rjdn(RJD)

=item rjd_to_mjdn(RJD)

=item rjd_to_djdn(RJD)

=item rjd_to_tjdn(RJD)

=item rjd_to_cjdn(RJD, ZONE)

=item rjd_to_rdn(RJD, ZONE)

=item rjd_to_ldn(RJD, ZONE)

=item mjd_to_jdn(MJD)

=item mjd_to_rjdn(MJD)

=item mjd_to_mjdn(MJD)

=item mjd_to_djdn(MJD)

=item mjd_to_tjdn(MJD)

=item mjd_to_cjdn(MJD, ZONE)

=item mjd_to_rdn(MJD, ZONE)

=item mjd_to_ldn(MJD, ZONE)

=item djd_to_jdn(DJD)

=item djd_to_rjdn(DJD)

=item djd_to_mjdn(DJD)

=item djd_to_djdn(DJD)

=item djd_to_tjdn(DJD)

=item djd_to_cjdn(DJD, ZONE)

=item djd_to_rdn(DJD, ZONE)

=item djd_to_ldn(DJD, ZONE)

=item tjd_to_jdn(TJD)

=item tjd_to_rjdn(TJD)

=item tjd_to_mjdn(TJD)

=item tjd_to_djdn(TJD)

=item tjd_to_tjdn(TJD)

=item tjd_to_cjdn(TJD, ZONE)

=item tjd_to_rdn(TJD, ZONE)

=item tjd_to_ldn(TJD, ZONE)

=item cjd_to_jdn(CJD, ZONE)

=item cjd_to_rjdn(CJD, ZONE)

=item cjd_to_mjdn(CJD, ZONE)

=item cjd_to_djdn(CJD, ZONE)

=item cjd_to_tjdn(CJD, ZONE)

=item cjd_to_cjdn(CJD)

=item cjd_to_rdn(CJD)

=item cjd_to_ldn(CJD)

=item rd_to_jdn(RD, ZONE)

=item rd_to_rjdn(RD, ZONE)

=item rd_to_mjdn(RD, ZONE)

=item rd_to_djdn(RD, ZONE)

=item rd_to_tjdn(RD, ZONE)

=item rd_to_cjdn(RD)

=item rd_to_rdn(RD)

=item rd_to_ldn(RD)

=item ld_to_jdn(LD, ZONE)

=item ld_to_rjdn(LD, ZONE)

=item ld_to_mjdn(LD, ZONE)

=item ld_to_djdn(LD, ZONE)

=item ld_to_tjdn(LD, ZONE)

=item ld_to_cjdn(LD)

=item ld_to_rdn(LD)

=item ld_to_ldn(LD)

These functions convert from a continuous day count to an integral day
count, possibly with separate fraction.  The input identifies a point in
time, as a continuous day count of input flavour.  If called in scalar
context, the function returns the day number of output flavour that
applies at that instant, throwing away information about the time of
(output-flavour) day.  If called in list context, the function returns a
list of two items: the day number and fractional day of output flavour,
which together identify the same point in time as the input.

These functions are not recommended, because the context-sensitive
return convention makes their use error-prone.  They are retained for
backward compatibility.  You should prefer to use the more specific
functions shown above.

=item jdn_to_jd(JDN, JDF)

=item jdn_to_rjd(JDN, JDF)

=item jdn_to_mjd(JDN, JDF)

=item jdn_to_djd(JDN, JDF)

=item jdn_to_tjd(JDN, JDF)

=item jdn_to_cjd(JDN, JDF, ZONE)

=item jdn_to_rd(JDN, JDF, ZONE)

=item jdn_to_ld(JDN, JDF, ZONE)

=item rjdn_to_jd(RJDN, RJDF)

=item rjdn_to_rjd(RJDN, RJDF)

=item rjdn_to_mjd(RJDN, RJDF)

=item rjdn_to_djd(RJDN, RJDF)

=item rjdn_to_tjd(RJDN, RJDF)

=item rjdn_to_cjd(RJDN, RJDF, ZONE)

=item rjdn_to_rd(RJDN, RJDF, ZONE)

=item rjdn_to_ld(RJDN, RJDF, ZONE)

=item mjdn_to_jd(MJDN, MJDF)

=item mjdn_to_rjd(MJDN, MJDF)

=item mjdn_to_mjd(MJDN, MJDF)

=item mjdn_to_djd(MJDN, MJDF)

=item mjdn_to_tjd(MJDN, MJDF)

=item mjdn_to_cjd(MJDN, MJDF, ZONE)

=item mjdn_to_rd(MJDN, MJDF, ZONE)

=item mjdn_to_ld(MJDN, MJDF, ZONE)

=item djdn_to_jd(DJDN, DJDF)

=item djdn_to_rjd(DJDN, DJDF)

=item djdn_to_mjd(DJDN, DJDF)

=item djdn_to_djd(DJDN, DJDF)

=item djdn_to_tjd(DJDN, DJDF)

=item djdn_to_cjd(DJDN, DJDF, ZONE)

=item djdn_to_rd(DJDN, DJDF, ZONE)

=item djdn_to_ld(DJDN, DJDF, ZONE)

=item tjdn_to_jd(TJDN, TJDF)

=item tjdn_to_rjd(TJDN, TJDF)

=item tjdn_to_mjd(TJDN, TJDF)

=item tjdn_to_djd(TJDN, TJDF)

=item tjdn_to_tjd(TJDN, TJDF)

=item tjdn_to_cjd(TJDN, TJDF, ZONE)

=item tjdn_to_rd(TJDN, TJDF, ZONE)

=item tjdn_to_ld(TJDN, TJDF, ZONE)

=item cjdn_to_jd(CJDN, CJDF, ZONE)

=item cjdn_to_rjd(CJDN, CJDF, ZONE)

=item cjdn_to_mjd(CJDN, CJDF, ZONE)

=item cjdn_to_djd(CJDN, CJDF, ZONE)

=item cjdn_to_tjd(CJDN, CJDF, ZONE)

=item cjdn_to_cjd(CJDN, CJDF)

=item cjdn_to_rd(CJDN, CJDF)

=item cjdn_to_ld(CJDN, CJDF)

=item rdn_to_jd(RDN, RDF, ZONE)

=item rdn_to_rjd(RDN, RDF, ZONE)

=item rdn_to_mjd(RDN, RDF, ZONE)

=item rdn_to_djd(RDN, RDF, ZONE)

=item rdn_to_tjd(RDN, RDF, ZONE)

=item rdn_to_cjd(RDN, RDF)

=item rdn_to_rd(RDN, RDF)

=item rdn_to_ld(RDN, RDF)

=item ldn_to_jd(LDN, LDF, ZONE)

=item ldn_to_rjd(LDN, LDF, ZONE)

=item ldn_to_mjd(LDN, LDF, ZONE)

=item ldn_to_djd(LDN, LDF, ZONE)

=item ldn_to_tjd(LDN, LDF, ZONE)

=item ldn_to_cjd(LDN, LDF)

=item ldn_to_rd(LDN, LDF)

=item ldn_to_ld(LDN, LDF)

These functions convert from an integral day count with separate fraction
to a continuous day count.  The input identifies a point in time, as
an integral day number of input flavour plus day fraction in the range
[0, 1).  The function returns the same point in time, represented as a
continuous day count of output flavour.

=item jdn_to_jdnn(JDN[, JDF])

=item jdn_to_rjdnn(JDN[, JDF])

=item jdn_to_mjdnn(JDN, JDF)

=item jdn_to_djdnn(JDN[, JDF])

=item jdn_to_tjdnn(JDN, JDF)

=item jdn_to_cjdnn(JDN, JDF, ZONE)

=item jdn_to_rdnn(JDN, JDF, ZONE)

=item jdn_to_ldnn(JDN, JDF, ZONE)

=item rjdn_to_jdnn(RJDN[, RJDF])

=item rjdn_to_rjdnn(RJDN[, RJDF])

=item rjdn_to_mjdnn(RJDN, RJDF)

=item rjdn_to_djdnn(RJDN[, RJDF])

=item rjdn_to_tjdnn(RJDN, RJDF)

=item rjdn_to_cjdnn(RJDN, RJDF, ZONE)

=item rjdn_to_rdnn(RJDN, RJDF, ZONE)

=item rjdn_to_ldnn(RJDN, RJDF, ZONE)

=item mjdn_to_jdnn(MJDN, MJDF)

=item mjdn_to_rjdnn(MJDN, MJDF)

=item mjdn_to_mjdnn(MJDN[, MJDF])

=item mjdn_to_djdnn(MJDN, MJDF)

=item mjdn_to_tjdnn(MJDN[, MJDF])

=item mjdn_to_cjdnn(MJDN, MJDF, ZONE)

=item mjdn_to_rdnn(MJDN, MJDF, ZONE)

=item mjdn_to_ldnn(MJDN, MJDF, ZONE)

=item djdn_to_jdnn(DJDN[, DJDF])

=item djdn_to_rjdnn(DJDN[, DJDF])

=item djdn_to_mjdnn(DJDN, DJDF)

=item djdn_to_djdnn(DJDN[, DJDF])

=item djdn_to_tjdnn(DJDN, DJDF)

=item djdn_to_cjdnn(DJDN, DJDF, ZONE)

=item djdn_to_rdnn(DJDN, DJDF, ZONE)

=item djdn_to_ldnn(DJDN, DJDF, ZONE)

=item tjdn_to_jdnn(TJDN, TJDF)

=item tjdn_to_rjdnn(TJDN, TJDF)

=item tjdn_to_mjdnn(TJDN[, TJDF])

=item tjdn_to_djdnn(TJDN, TJDF)

=item tjdn_to_tjdnn(TJDN[, TJDF])

=item tjdn_to_cjdnn(TJDN, TJDF, ZONE)

=item tjdn_to_rdnn(TJDN, TJDF, ZONE)

=item tjdn_to_ldnn(TJDN, TJDF, ZONE)

=item cjdn_to_jdnn(CJDN, CJDF, ZONE)

=item cjdn_to_rjdnn(CJDN, CJDF, ZONE)

=item cjdn_to_mjdnn(CJDN, CJDF, ZONE)

=item cjdn_to_djdnn(CJDN, CJDF, ZONE)

=item cjdn_to_tjdnn(CJDN, CJDF, ZONE)

=item cjdn_to_cjdnn(CJDN[, CJDF])

=item cjdn_to_rdnn(CJDN[, CJDF])

=item cjdn_to_ldnn(CJDN[, CJDF])

=item rdn_to_jdnn(RDN, RDF, ZONE)

=item rdn_to_rjdnn(RDN, RDF, ZONE)

=item rdn_to_mjdnn(RDN, RDF, ZONE)

=item rdn_to_djdnn(RDN, RDF, ZONE)

=item rdn_to_tjdnn(RDN, RDF, ZONE)

=item rdn_to_cjdnn(RDN[, RDF])

=item rdn_to_rdnn(RDN[, RDF])

=item rdn_to_ldnn(RDN[, RDF])

=item ldn_to_jdnn(LDN, LDF, ZONE)

=item ldn_to_rjdnn(LDN, LDF, ZONE)

=item ldn_to_mjdnn(LDN, LDF, ZONE)

=item ldn_to_djdnn(LDN, LDF, ZONE)

=item ldn_to_tjdnn(LDN, LDF, ZONE)

=item ldn_to_cjdnn(LDN[, LDF])

=item ldn_to_rdnn(LDN[, LDF])

=item ldn_to_ldnn(LDN[, LDF])

These functions convert from an integral day count with separate fraction
to an integral day count.  The input identifies a point in time, as an
integral day number of input flavour plus day fraction in the range
[0, 1).  The function returns the day number of output flavour that
applies at that instant.  The process throws away information about
the time of (output-flavour) day.  If converting between systems that
delimit days identically (e.g., between JD and RJD), the day fraction
makes no difference and may be omitted from the input.

=item jdn_to_jdnf(JDN, JDF)

=item jdn_to_rjdnf(JDN, JDF)

=item jdn_to_mjdnf(JDN, JDF)

=item jdn_to_djdnf(JDN, JDF)

=item jdn_to_tjdnf(JDN, JDF)

=item jdn_to_cjdnf(JDN, JDF, ZONE)

=item jdn_to_rdnf(JDN, JDF, ZONE)

=item jdn_to_ldnf(JDN, JDF, ZONE)

=item rjdn_to_jdnf(RJDN, RJDF)

=item rjdn_to_rjdnf(RJDN, RJDF)

=item rjdn_to_mjdnf(RJDN, RJDF)

=item rjdn_to_djdnf(RJDN, RJDF)

=item rjdn_to_tjdnf(RJDN, RJDF)

=item rjdn_to_cjdnf(RJDN, RJDF, ZONE)

=item rjdn_to_rdnf(RJDN, RJDF, ZONE)

=item rjdn_to_ldnf(RJDN, RJDF, ZONE)

=item mjdn_to_jdnf(MJDN, MJDF)

=item mjdn_to_rjdnf(MJDN, MJDF)

=item mjdn_to_mjdnf(MJDN, MJDF)

=item mjdn_to_djdnf(MJDN, MJDF)

=item mjdn_to_tjdnf(MJDN, MJDF)

=item mjdn_to_cjdnf(MJDN, MJDF, ZONE)

=item mjdn_to_rdnf(MJDN, MJDF, ZONE)

=item mjdn_to_ldnf(MJDN, MJDF, ZONE)

=item djdn_to_jdnf(DJDN, DJDF)

=item djdn_to_rjdnf(DJDN, DJDF)

=item djdn_to_mjdnf(DJDN, DJDF)

=item djdn_to_djdnf(DJDN, DJDF)

=item djdn_to_tjdnf(DJDN, DJDF)

=item djdn_to_cjdnf(DJDN, DJDF, ZONE)

=item djdn_to_rdnf(DJDN, DJDF, ZONE)

=item djdn_to_ldnf(DJDN, DJDF, ZONE)

=item tjdn_to_jdnf(TJDN, TJDF)

=item tjdn_to_rjdnf(TJDN, TJDF)

=item tjdn_to_mjdnf(TJDN, TJDF)

=item tjdn_to_djdnf(TJDN, TJDF)

=item tjdn_to_tjdnf(TJDN, TJDF)

=item tjdn_to_cjdnf(TJDN, TJDF, ZONE)

=item tjdn_to_rdnf(TJDN, TJDF, ZONE)

=item tjdn_to_ldnf(TJDN, TJDF, ZONE)

=item cjdn_to_jdnf(CJDN, CJDF, ZONE)

=item cjdn_to_rjdnf(CJDN, CJDF, ZONE)

=item cjdn_to_mjdnf(CJDN, CJDF, ZONE)

=item cjdn_to_djdnf(CJDN, CJDF, ZONE)

=item cjdn_to_tjdnf(CJDN, CJDF, ZONE)

=item cjdn_to_cjdnf(CJDN, CJDF)

=item cjdn_to_rdnf(CJDN, CJDF)

=item cjdn_to_ldnf(CJDN, CJDF)

=item rdn_to_jdnf(RDN, RDF, ZONE)

=item rdn_to_rjdnf(RDN, RDF, ZONE)

=item rdn_to_mjdnf(RDN, RDF, ZONE)

=item rdn_to_djdnf(RDN, RDF, ZONE)

=item rdn_to_tjdnf(RDN, RDF, ZONE)

=item rdn_to_cjdnf(RDN, RDF)

=item rdn_to_rdnf(RDN, RDF)

=item rdn_to_ldnf(RDN, RDF)

=item ldn_to_jdnf(LDN, LDF, ZONE)

=item ldn_to_rjdnf(LDN, LDF, ZONE)

=item ldn_to_mjdnf(LDN, LDF, ZONE)

=item ldn_to_djdnf(LDN, LDF, ZONE)

=item ldn_to_tjdnf(LDN, LDF, ZONE)

=item ldn_to_cjdnf(LDN, LDF)

=item ldn_to_rdnf(LDN, LDF)

=item ldn_to_ldnf(LDN, LDF)

These functions convert from one integral day count with separate
fraction to another.  The input identifies a point in time, as an
integral day number of input flavour plus day fraction in the range
[0, 1).  The function returns a list of two items: the day number and
fractional day of output flavour, which together identify the same point
in time as the input.

=item jdn_to_jdn(JDN[, JDF])

=item jdn_to_rjdn(JDN[, JDF])

=item jdn_to_mjdn(JDN, JDF)

=item jdn_to_djdn(JDN[, JDF])

=item jdn_to_tjdn(JDN, JDF)

=item jdn_to_cjdn(JDN, JDF, ZONE)

=item jdn_to_rdn(JDN, JDF, ZONE)

=item jdn_to_ldn(JDN, JDF, ZONE)

=item rjdn_to_jdn(RJDN[, RJDF])

=item rjdn_to_rjdn(RJDN[, RJDF])

=item rjdn_to_mjdn(RJDN, RJDF)

=item rjdn_to_djdn(RJDN[, RJDF])

=item rjdn_to_tjdn(RJDN, RJDF)

=item rjdn_to_cjdn(RJDN, RJDF, ZONE)

=item rjdn_to_rdn(RJDN, RJDF, ZONE)

=item rjdn_to_ldn(RJDN, RJDF, ZONE)

=item mjdn_to_jdn(MJDN, MJDF)

=item mjdn_to_rjdn(MJDN, MJDF)

=item mjdn_to_mjdn(MJDN[, MJDF])

=item mjdn_to_djdn(MJDN, MJDF)

=item mjdn_to_tjdn(MJDN[, MJDF])

=item mjdn_to_cjdn(MJDN, MJDF, ZONE)

=item mjdn_to_rdn(MJDN, MJDF, ZONE)

=item mjdn_to_ldn(MJDN, MJDF, ZONE)

=item djdn_to_jdn(DJDN[, DJDF])

=item djdn_to_rjdn(DJDN[, DJDF])

=item djdn_to_mjdn(DJDN, DJDF)

=item djdn_to_djdn(DJDN[, DJDF])

=item djdn_to_tjdn(DJDN, DJDF)

=item djdn_to_cjdn(DJDN, DJDF, ZONE)

=item djdn_to_rdn(DJDN, DJDF, ZONE)

=item djdn_to_ldn(DJDN, DJDF, ZONE)

=item tjdn_to_jdn(TJDN, TJDF)

=item tjdn_to_rjdn(TJDN, TJDF)

=item tjdn_to_mjdn(TJDN[, TJDF])

=item tjdn_to_djdn(TJDN, TJDF)

=item tjdn_to_tjdn(TJDN[, TJDF])

=item tjdn_to_cjdn(TJDN, TJDF, ZONE)

=item tjdn_to_rdn(TJDN, TJDF, ZONE)

=item tjdn_to_ldn(TJDN, TJDF, ZONE)

=item cjdn_to_jdn(CJDN, CJDF, ZONE)

=item cjdn_to_rjdn(CJDN, CJDF, ZONE)

=item cjdn_to_mjdn(CJDN, CJDF, ZONE)

=item cjdn_to_djdn(CJDN, CJDF, ZONE)

=item cjdn_to_tjdn(CJDN, CJDF, ZONE)

=item cjdn_to_cjdn(CJDN[, CJDF])

=item cjdn_to_rdn(CJDN[, CJDF])

=item cjdn_to_ldn(CJDN[, CJDF])

=item rdn_to_jdn(RDN, RDF, ZONE)

=item rdn_to_rjdn(RDN, RDF, ZONE)

=item rdn_to_mjdn(RDN, RDF, ZONE)

=item rdn_to_djdn(RDN, RDF, ZONE)

=item rdn_to_tjdn(RDN, RDF, ZONE)

=item rdn_to_cjdn(RDN[, RDF])

=item rdn_to_rdn(RDN[, RDF])

=item rdn_to_ldn(RDN[, RDF])

=item ldn_to_jdn(LDN, LDF, ZONE)

=item ldn_to_rjdn(LDN, LDF, ZONE)

=item ldn_to_mjdn(LDN, LDF, ZONE)

=item ldn_to_djdn(LDN, LDF, ZONE)

=item ldn_to_tjdn(LDN, LDF, ZONE)

=item ldn_to_cjdn(LDN[, LDF])

=item ldn_to_rdn(LDN[, LDF])

=item ldn_to_ldn(LDN[, LDF])

These functions convert from an integral day count with separate fraction
to an integral day count, possibly with separate fraction.  The input
identifies a point in time, as an integral day number of input flavour
plus day fraction in the range [0, 1).  If called in scalar context, the
function returns the day number of output flavour that applies at that
instant, throwing away information about the time of (output-flavour) day.
If called in list context, the function returns a list of two items:
the day number and fractional day of output flavour, which together
identify the same point in time as the input.

If converting between systems that delimit days identically (e.g.,
between JD and RJD), the day fraction makes no difference to the integral
day number of the output, and may be omitted from the input.  If the day
fraction is extracted from the output when it wasn't supplied as input,
it will default to zero.

These functions are not recommended, because the context-sensitive
return convention makes their use error-prone.  They are retained for
backward compatibility.  You should prefer to use the more specific
functions shown above.

=cut

eval { local $SIG{__DIE__};
	require POSIX;
	*_floor = \&POSIX::floor;
};
if($@ ne "") {
	*_floor = sub($) {
		my $i = int($_[0]);
		return $i == $_[0] || $_[0] > 0 ? $i : $i - 1;
	}
}

sub _check_dn($$) {
	croak "purported day number $_[0] is not an integer"
		unless ref($_[0]) ? $_[0]->is_int : $_[0] == int($_[0]);
	croak "purported day fraction $_[1] is out of range [0, 1)"
		unless $_[1] >= 0 && $_[1] < 1;
}

sub _ret_dnn($) {
	my $dn = ref($_[0]) eq "Math::BigRat" ?
			$_[0]->copy->bfloor : _floor($_[0]);
	return $dn;
}

sub _ret_dnf($) {
	my $dn = &_ret_dnn;
	return ($dn, $_[0] - $dn);
}

sub _ret_dn($) {
	return wantarray ? &_ret_dnf : &_ret_dnn;
}

foreach my $src (keys %jd_flavours) { foreach my $dst (keys %jd_flavours) {
	my $ediff = $jd_flavours{$src}->{epoch_jd} -
			$jd_flavours{$dst}->{epoch_jd};
	my $ediffh = $ediff == int($ediff) ? 0 : 0.5;
	my $src_zone = !!$jd_flavours{$src}->{zone};
	my $dst_zone = !!$jd_flavours{$dst}->{zone};
	my($zp, $z1, $z2);
	if($src_zone == $dst_zone) {
		$zp = $z1 = $z2 = "";
	} else {
		$zp = "\$";
		my $zsign = $src_zone ? "-" : "+";
		$z1 = "$zsign \$_[1]";
		$z2 = "$zsign \$_[2]";
	}
	eval "sub ${src}_to_${dst}(\$${zp}) { \$_[0] + (${ediff}) ${z1} }";
	push @EXPORT_OK, "${src}_to_${dst}";
	eval "sub ${src}_to_${dst}nn(\$${zp}) {
		_ret_dnn(\$_[0] + (${ediff}) ${z1})
	}";
	push @EXPORT_OK, "${src}_to_${dst}nn";
	eval "sub ${src}_to_${dst}nf(\$${zp}) {
		_ret_dnf(\$_[0] + (${ediff}) ${z1})
	}";
	push @EXPORT_OK, "${src}_to_${dst}nf";
	eval "sub ${src}_to_${dst}n(\$${zp}) {
		_ret_dn(\$_[0] + (${ediff}) ${z1})
	}";
	push @EXPORT_OK, "${src}_to_${dst}n";
	eval "sub ${src}n_to_${dst}(\$\$${zp}) {
		_check_dn(\$_[0], \$_[1]);
		\$_[0] + \$_[1] + (${ediff}) ${z2}
	}";
	push @EXPORT_OK, "${src}n_to_${dst}";
	my($tp, $tc);
	if($ediffh == 0 && $src_zone == $dst_zone) {
		$tp = ";";
		$tc = "push \@_, 0 if \@_ == 1;";
	} else {
		$tp = $tc = "";
	}
	eval "sub ${src}n_to_${dst}nn(\$${tp}\$${zp}) { $tc
		_check_dn(\$_[0], \$_[1]);
		_ret_dnn(\$_[0] + \$_[1] + ($ediff) ${z2})
	}";
	push @EXPORT_OK, "${src}n_to_${dst}nn";
	eval "sub ${src}n_to_${dst}nf(\$\$${zp}) {
		_check_dn(\$_[0], \$_[1]);
		_ret_dnf(\$_[0] + \$_[1] + ($ediff) ${z2})
	}";
	push @EXPORT_OK, "${src}n_to_${dst}nf";
	eval "sub ${src}n_to_${dst}n(\$${tp}\$${zp}) { $tc
		_check_dn(\$_[0], \$_[1]);
		_ret_dn(\$_[0] + \$_[1] + ($ediff) ${z2})
	}";
	push @EXPORT_OK, "${src}n_to_${dst}n";
} }

=back

=head1 SEE ALSO

L<Date::ISO8601>,
L<Date::MSD>,
L<DateTime>,
L<Time::UTC>

=head1 AUTHOR

Andrew Main (Zefram) <zefram@fysh.org>

=head1 COPYRIGHT

Copyright (C) 2006, 2007, 2009, 2010, 2011, 2017
Andrew Main (Zefram) <zefram@fysh.org>

=head1 LICENSE

This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.

=cut

1;