Bug #12766: easter_days breaks for year before 1753
| From: | martin at diers dot cc | Date: | Wed, 15 Aug 2001 14:51:32 +0000 |
| Subject: | Bug #12766: easter_days breaks for year before 1753 | ||
| Groups: | php.dev | ||
| Request: | Send a blank email to php-dev+get-63282@lists.php.net to get a copy of this message | ||
From: martin@diers.cc
Operating system: Linux 2.4.x
PHP version: 4.0.6
PHP Bug Type: Calendar related
Bug description: easter_days breaks for year before 1753
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);
}
--
Edit bug report at: http://bugs.php.net/?id=12766&edit=1