This is a trick I learned from tye. You can calculate a number that is so absurdly high, that it must be stored internally as inf (infinite).

use constant INF => 9**9E9;
print INF;
[download]

Output:

1.#INF

Oddly enough, comparisons still work, in every Perl version I've tested so far:

use constant INF => 9**9E9;
local($\, $,) = ("\n", "\t");
for my $e (305 .. 310) {
    my $n = 10**$e;
    print $e, $n, INF > $n || 0, -$n, -(INF) < - $n || 0;
}
[download]

Result:

305    1e+305    1    -1e+305    1
306    1e+306    1    -1e+306    1
307    1e+307    1    -1e+307    1
308    1e+308    1    -1e+308    1
309    1.#INF    0    -1.#INF    0
310    1.#INF    0    -1.#INF    0
[download]

(On another perl I see "inf" instead of "1.#INF", but other results are identical.)

As you can see, even the unary minus sign (negate) still works as it ought to.

Unfortunately(?) INF is still not bigger than INF, but... I guess that won't matter any more, will it?