Bug #12766 Updated: easter_days breaks for year before 1753
| From: | martin at diers dot cc | Date: | Wed, 15 Aug 2001 18:25:16 +0000 |
| Subject: | Bug #12766 Updated: easter_days breaks for year before 1753 | ||
| References: | 1 | Groups: | php.dev |
| Request: | Send a blank email to php-dev+get-63315@lists.php.net to get a copy of this message | ||
ID: 12766
User updated by: martin@diers.cc
Reported By: martin@diers.cc
Status: Open
Bug Type: Calendar related
Operating System: Linux 2.4.x
PHP Version: 4.0.6
New Comment:
Based on the documentation for the easter_days command, this behaviour would appear to be
deliberate. It seems that the easter calculation is changed over to the Julian formula for all dates
prior to 1753, because that is the year that Britain and its colonies finally switched to the
Gregorian calendar. However, that does not change the fact that since 1582, the rest of Europe was
using the Gregorian calendar.
This being the case, it would make since to be able to calculate the date of Easter for the range
1582-1752 using either the Julian formula (which is simply based on cycles of the moon) or the
Gregorian formula (which is far more complex). To implement this, an optional switch could be added
to the easter_days function which defaults to the Julian formula for that date range, but allows the
user to specify the Gregorian formula instead.
Previous Comments:
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[2001-08-15 10:51:32] martin@diers.cc
The easter_days function returns bad data for years <= 1752. Here is a way to verify. Because
Easter always falls on a Sunday, the following function should always return "Sunday":
function EasterDOW($year) {
$jdayc = easter_days($year);
$jdmar21 = gregoriantojd(3, 21, $year);
$jdeaster = $jdmar21 + $jdayc;
return JDDayOfWeek($jdeaster, 1);
}
The formula for calculating easter has been the same since 1582. The standerd Delambre Easter
algorithm is able to generate the date of easter for any gregorian date after 1582. The following
function may be used to duplicate the functionality of easter_days for any date since 1582:
function easter_days2($year) {
#First calculate the date of easter using
#Delambre's algorithm.
$a = $year % 19;
$b = floor($year / 100);
$c = $year % 100;
$d = floor($b / 4);
$e = $b % 4;
$f = floor(($b + 8) / 25);
$g = floor(($b - $f + 1) / 3);
$h = (19 * $a + $b - $d - $g + 15) % 30;
$i = floor($c / 4);
$k = $c % 4;
$l = (32 + 2 * $e + 2 * $i - $h - $k) % 7;
$m = floor(($a + 11 * $h + 22 * $l) / 451);
$n = ($h + $l - 7 * $m + 114);
$month = floor($n / 31);
$day = $n % 31 + 1;
#Return the difference between the JulianDayCount
#for easter and March 21'st of the same year,
#in order to duplicate the functionality of the
#easter_days function
return GregorianToJD($month, $day, $year) - GregorianToJD(3,21,$year);
}
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Edit this bug report at http://bugs.php.net/?id=12766&edit=1