php准确计算复活节日期的方法

<?php
function isleapyear( $nyear ) {
 if((($nyear % 4 == 0) and !($nyear % 100 == 0)) and ($nyear % 400 != 0))
 {
  return true;
 } else {
  return false;
 }
}
function div( $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 = div( $nyear, 100 ) + 1;
  $nksj = div( 3 * $njhd, 4 ) - 12;
  $nkorr = div( 8 * $njhd + 5, 25 ) - 5;
  $nso = div( 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 = div( 20 * $nnm, 611 ) - 2;
  // day
  $nnt = $nn;
  $nnt = $nn;
  if ( $nnt > ( 59 + $na )) {
   $nnt = $nnt + 2 - $na;
  }
  $nnt = $nnt + 91;
  $nm = div( 20 * $nnt, 611 );
  $nday = $nnt - div( 611 * $nm, 20 );
  $dteastersunday = mktime( 0,0,0,$nmonth,$nday,$nyear );
 }
 return $dteastersunday;
}
?>