Well, you could of course build yourself a 64bit perl, then you can go up to 9223372036854775807. Or else, you can use Math::BigInt. Or Inline::BC.

Here's an Inline::BC solution:

use strict;
use warnings;
 
use Inline 'BC'; 
 
my @nums = qw /0 1 5 10 16 2147483647 9223372036854775807      
               124897514814098457204985981709857243095827435/;

foreach my $number (@nums) {
    print "$number: ", np ($number);        
}
 
__DATA__
__BC__
define np (i) { 
    auto j;
    while (i) {    
        i /= 2;
        j += 1;
    }
    return (2 ^ j)
}

0: 1
1: 2
5: 8
10: 16
16: 32
2147483647: 2147483648
9223372036854775807: 9223372036854775808
124897514814098457204985981709857243095827435: 17840596158824498513228
+5746181186892047843328
[download]

And here's a Math::BigInt one:

use strict;
use warnings;

use Math::BigInt;

my @nums = qw /0 1 5 10 16 2147483647 9223372036854775807
               124897514814098457204985981709857243095827435/;

foreach my $number (@nums) {
    $number    = Math::BigInt -> new ($number);
    my $result = Math::BigInt -> new (1);

    print "$number: ";
    until ($number == 0) {
        $number /= 2;
        $result *= 2;
    }
    print "$result\n";

}

__END__
0: 1
1: 2
5: 8
10: 16
16: 32
2147483647: 2147483648
9223372036854775807: 9223372036854775808
124897514814098457204985981709857243095827435: 17840596158824498513228
+5746181186892047843328
[download]

Abigail