use strict;
use warnings;

my $HIGH_BITS =  0xFFFFFFFF << 28;
printf "%X\n", $HIGH_BITS;
# prints: FFFFFFFF0000000
# each hex digit is 4 bits, 7 zeroes x4 = 28 bits left shifted

##</code><code>##

>perl -le "my $HIGH_BITS = unpack "l", pack "l", 0xFFFFFFFF << 28; print $HIGH_BITS; "
-268435456