イースターの正確な日付を計算する PHP メソッド

<?PHP
function isLeapYear( $nYEAR ) {
 if((($nYEAR % 4 == 0) AND !($nYEAR % 100 == 0)) AND ($nYEAR % 400 != 0))
 {
  return TRUE;
 } else {
  return FALSE;
 }
}
function p( $a, $b ){
 return( $a - ( $a % $b )) / $b;
}
function easterSunday( $nYEAR ) {
 // The function is able to calculate the date 
 //of eastersunday back to the year 325,
 // but mktime() starts at 1970-01-01!
 if ( $nYEAR < 1970 ) {
  $dtEasterSunday = mktime( 1,1,1,1,1,1970 );
 } else {
  $nGZ = ( $nYEAR % 19 ) + 1;
  $nJHD = p( $nYEAR, 100 ) + 1;
  $nKSJ = p( 3 * $nJHD, 4 ) - 12;
  $nKORR = p( 8 * $nJHD + 5, 25 ) - 5;
  $nSO = p( 5 * $nYEAR, 4 ) - $nKSJ - 10;
  $nEPAKTE = (( 11 * $nGZ + 20 + $nKORR - $nKSJ ) % 30 );
  if (( $nEPAKTE == 25 OR $nGZ == 11 ) AND $nEPAKTE == 24 ) {
   $nEPAKTE = $nEPAKTE + 1;
  }
  $nN = 44 - $nEPAKTE;
  if( $nN < 21 ) {
   $nN = $nN + 30;
  }
  $nN = $nN + 7 - (( $nSO + $nN ) % 7 );
  $nN = $nN + isLeapYear( $nYEAR );
  $nN = $nN + 59;
  $nA = isLeapYear( $nYEAR );
  // Month
  $nNM = $nN;
  if ( $nNM > ( 59 + $nA )) {
   $nNM = $nNM + 2 - $nA;
  }
  $nNM = $nNM + 91;
  $nMONTH = p( 20 * $nNM, 611 ) - 2;
  // Day
  $nNT = $nN;
  $nNT = $nN;
  if ( $nNT > ( 59 + $nA )) {
   $nNT = $nNT + 2 - $nA;
  }
  $nNT = $nNT + 91;
  $nM = p( 20 * $nNT, 611 );
  $nDAY = $nNT - p( 611 * $nM, 20 );
  $dtEasterSunday = mktime( 0,0,0,$nMONTH,$nDAY,$nYEAR );
 }
 return $dtEasterSunday;
}
?>