Description:
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Sorry for my bad english.

PHP v5.1.1 : when using strtotime function intensively 
in my script the performance as reduced and the script is generate in 0,250 s ?

With PHP 5.0.5, my script is generate in 0,055 s !

I'm test my script with PHP 5.1.1 without strtotime function  -> this page was generate in 0,050 s !

Reproduce code:
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for ($i=1; $i<=30; $i++) {
$timestamp = strtotime("-". (30-$i) ." day");
}

for ( $i = 0; $i < 30; $i++ ){
 $j = 29 - $i;
 $time_colone	= date("y",strtotime("-$j day")).date("z",strtotime("-$j day"));

}