PHP Can't convert hex over 7fffffff ?

In php, you can seamlessly convert strings representing both decimal and hex numbers to integers using 0 + string.

An (int) cast does not do this, and other methods gave me problems. Anyway:

print '<p>';

$hx = "0x2345e";

$n = 0 + $hx;

print "$n <br>";

$hx = "0xcb623";

$n = 0 + $hx;

print "$n <br>";

$hx = "0xcb511df6";

$n = 0 + $hx;

print "$n </p>";

Expected output:

144478

833059

-883876362

(or a large positive number).

Actual output:

144478

833059

0

Doing intval($hx,16); returns 2147483647 which is 0x7fffffff.

How to deal with hex strings representing numbers >0x7fffffff ?