Description:
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I believe it's not a bug, but it's a really good way to lock down the server for a couple of seconds.

Anyway, mktime does not check if 'year' is a valid number. It accepts any integer value and starts counting the seconds.

IMO mktime should have some limit after which the date is considered invalid and it returns FALSE without even starting to count.

Reproduce code:
---------------
<?php
        $start = microtime(1);
        $a = mktime(1, 1, 1, 1, 1, 11111111111);
        var_dump($a);
        echo number_format(microtime(1) - $start, 2)."\n";
?>


Expected result:
----------------
bool(false)
0.00

Actual result:
--------------
bool(false)
44.57