Description:
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From http://www.reddit.com/r/PHP/comments/1hx7qz/what_is_going_on_here_how_do_i_fix_t

function calcExp ($gmpC) {
    //make sure gc is on
    gc_enable();

    for ($i=0; $i<2000000000; $i++) {
        $gmpTempC = $gmpC;
        gc_collect_cycles();
    }
    return false;
}

$num = gmp_init('1094189891312342345461854');
print "\n";
calcExp($num);