<reference id="ref.calendar">
  <title>Calendar Functions</title>
  <titleabbrev>Calendar</titleabbrev>

  <partintro>
   <para>
    The calendar functions are only available if you have compiled the
    calendar extension in dl/calendar. Read dl/README for instructions on
    using it.
   </para>
   <para>
    The Calendar extension in PHP presents a series of functions to
    simplify converting between different calendar formats.  The
    intermediary or standard it is based on is the Julian Day Count.
    The Julian Day Count is a count of days starting way earlier than
    any date most people would need to track (somewhere around
    4000bc).  To convert between calendar systems, you must first
    convert to Julian Day Count, then to the calendar system of your
    choice.  Julian Day Count is very different from the Julian
    Calendar!  For more information on calendar systems visit <ulink
    url="http://genealogy.org/~scottlee/cal-overview.html">http://genealogy.org/~scottlee/cal-overview.html</ulink>.
    Excerpts from this page are included in these instructions, and
    are in quotes
  </partintro>

    <refentry id="function.jdtogregorian">
      <refnamediv>
	<refname>JDToGregorian</refname>
	<refpurpose>Converts Julian Day Count to Gregorian date</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
          <funcdef>string <function>jdtogregorian</function></funcdef>
	  <paramdef>int <parameter>julianday</parameter></paramdef>
	</funcsynopsis>
        <para>
         Converts Julian Day Count to a string containing the
         Gregorian date in the format of "month/day/year"
      </refsect1>
    </refentry>

    <refentry id="function.gregoriantojd">
      <refnamediv>
	<refname>GregorianToJD</refname> 
        <refpurpose>Converts a Gregorian date to Julian Day
         Count</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>int <function>gregoriantojd</function></funcdef>
	  <paramdef>int <parameter>month</parameter></paramdef>
	  <paramdef>int <parameter>day</parameter></paramdef>
	  <paramdef>int <parameter>year</parameter></paramdef>
	</funcsynopsis>
	<para>
         Valid Range for Gregorian Calendar 4714 B.C. to 9999 A.D.
        <para>
         Although this software can handle dates all the way back to
         4714 B.C., such use may not be meaningful. The Gregorian
         calendar was not instituted until October 15, 1582 (or
         October 5, 1582 in the Julian calendar). Some countries did
         not accept it until much later. For example, Britain
         converted in 1752, The USSR in 1918 and Greece in 1923. Most
         European countries used the Julian calendar prior to the
         Gregorian.

<example>
	    <title>Calendar functions</title>
	    <programlisting role=php>
&lt;?php
$jd = GregorianToJD(10,11,1970);
echo("$jd\n");
$gregorian = JDToGregorian($jd);
echo("$gregorian\n");
?>
</programlisting>
</example>

      </refsect1>
    </refentry>
 
    <refentry id="function.jdtojulian">
      <refnamediv>
	<refname>JDToJulian</refname> 
        <refpurpose>Converts a Julian Calendar date to Julian Day
 	 Count</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>string <function>jdtojulian</function></funcdef>
	  <paramdef>int <parameter>julianday</parameter></paramdef>
	</funcsynopsis>
	<para>
         Converts Julian Day Count to a string containing the Julian
         Calendar Date in the format of "month/day/year".
      </refsect1>
    </refentry>

    <refentry id="function.juliantojd">
      <refnamediv>
	<refname>JulianToJD</refname> 
        <refpurpose>Converts a Julian Calendar date to Julian Day
         Count</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>int <function>juliantojd</function></funcdef>
	  <paramdef>int <parameter>month</parameter></paramdef>
	  <paramdef>int <parameter>day</parameter></paramdef>
	  <paramdef>int <parameter>year</parameter></paramdef>
	</funcsynopsis>
        <para>
         Valid Range for Julian Calendar 4713 B.C. to 9999 A.D.
        <para>
         Although this software can handle dates all the way back to
         4713 B.C., such use may not be meaningful. The calendar was
         created in 46 B.C., but the details did not stabilize until
         at least 8 A.D., and perhaps as late at the 4th
         century. Also, the beginning of a year varied from one
         culture to another - not all accepted January as the first
         month.
      </refsect1>
    </refentry>

    <refentry id="function.jdtojewish">
      <refnamediv>
	<refname>JDToJewish</refname>
	<refpurpose>Converts a Julian Day Count to the Jewish
         Calendar</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>string <function>jdtojewish</function></funcdef>
	  <paramdef>int <parameter>julianday</parameter></paramdef>
	</funcsynopsis>
        <para>
         Converts a Julian Day Count the the Jewish Calendar.
      </refsect1>
    </refentry>

    <refentry id="function.jewishtojd">
      <refnamediv>
	<refname>JewishToJD</refname> 
        <refpurpose>Converts a date in the Jewish Calendar to Julian
         Day Count</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>int <function>jewishtojd</function></funcdef>
	  <paramdef>int <parameter>month</parameter></paramdef>
	  <paramdef>int <parameter>day</parameter></paramdef>
	  <paramdef>int <parameter>year</parameter></paramdef>
	</funcsynopsis>
        <para>
         Valid Range Although this software can handle dates all the
         way back to the year 1 (3761 B.C.), such use may not be
         meaningful.
        <para>
         The Jewish calendar has been in use for several thousand
         years, but in the early days there was no formula to
         determine the start of a month. A new month was started when
         the new moon was first observed.
      </refsect1>
    </refentry>

    <refentry id="function.jdtofrench">
      <refnamediv>
	<refname>JDToFrench</refname>
	<refpurpose>Converts a Julian Day Count to the French
         Republican Calendar</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>string <function>jdtofrench</function></funcdef>
	  <paramdef>int <parameter>month</parameter></paramdef>
	  <paramdef>int <parameter>day</parameter></paramdef>
	  <paramdef>int <parameter>year</parameter></paramdef>
	</funcsynopsis>
        <para>
         Converts a Julian Day Count to the French Republican
         Calendar.
      </refsect1>
    </refentry>

    <refentry id="function.frenchtojd">
      <refnamediv>
	<refname>FrenchToJD</refname>
	<refpurpose>Converts a date from the French Republican
         Calendar to a Julian Day Count</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>int <function>frenchtojd</function></funcdef>
	  <paramdef>int <parameter>month</parameter></paramdef>
	  <paramdef>int <parameter>day</parameter></paramdef>
	  <paramdef>int <parameter>year</parameter></paramdef>
	</funcsynopsis>
        <para>
	 Converts a date from the French Republican Calendar to a
	 Julian Day Count
        <para>
         These routines only convert dates in years 1 through 14
         (Gregorian dates 22 September 1792 through 22 September
         1806). This more than covers the period when the calendar was
         in use.
      </refsect1>
    </refentry>

    <refentry id="function.jdmonthname">
      <refnamediv>
	<refname>JDMonthName</refname>
	<refpurpose>Returns a month name</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>string <function>jdmonthname</function></funcdef>
	  <paramdef>int <parameter>julianday</parameter></paramdef>
	  <paramdef>int <parameter>mode</parameter></paramdef>
	</funcsynopsis>
        <para>
         Returns a string containing a month name.
         <parameter>mode</parameter> tells this function which
         calendar to convert the Julian Day Count to, and what type of
         month names are to be returned.


     <table>
      <title>Calendar modes</title>
      <tgroup cols="2">
       <thead>
	<row>
	 <entry>Mode</entry>
	 <entry>Meaning</entry>
	</row>
       </thead>
       <tbody>
	<row>
	 <entry>0</entry>
	 <entry>Gregorian - apreviated</entry>
	</row>
	<row>
	 <entry>1</entry>
	 <entry>Gregorian</entry>
	</row>
	<row>
	 <entry>2</entry>
	 <entry>Julian - apreviated</entry>
	</row>
	<row>
	 <entry>3</entry>
	 <entry>Julian</entry>
	</row>
	<row>
	 <entry>4</entry>
	 <entry>Jewish</entry>
	</row>
	<row>
	 <entry>5</entry>
	 <entry>French Republican</entry>
	</row>
       </tbody>
      </tgroup>
     </table>

      </refsect1>
    </refentry>

    <refentry id="function.jddayofweek">
      <refnamediv>
	<refname>JDDayOfWeek</refname>
	<refpurpose>Returns the day of the week</refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>
	<funcsynopsis>
	  <funcdef>mixed <function>jddayofweek</function></funcdef>
	  <paramdef>int <parameter>julianday</parameter></paramdef>
	  <paramdef>int <parameter>mode</parameter></paramdef>
	</funcsynopsis>
        <para>
         Returns the day of the week.  Can return a string or an int
         depending on the mode.

     <table>
      <title>Calendar week modes</title>
      <tgroup cols="2">
       <thead>
	<row>
	 <entry>Mode</entry>
	 <entry>Meaning</entry>
	</row>
       </thead>
       <tbody>
	<row>
	 <entry>0</entry> <entry>returns the day number as an int
	 (0=sunday, 1=monday, etc)</entry>
	</row>
	<row>
	 <entry>1</entry> <entry>returns string containing the day of
	 week (english-gregorian)</entry>
	</row>
	<row>
	 <entry>2</entry> <entry>returns a string containing the
	 abreviated day of week (english-gregorian)</entry>
	</row>
       </tbody>
      </tgroup>
     </table>

      </refsect1>
    </refentry>

 </reference>

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