$stream =~ s/0/0000 /g;
$stream =~ s/1/1111 /g;

##</code><code>##

$stream =~ s/(.)/$1$1$1$1 /g; # could be rewritten using /e and x 4


##</code><code>##

$stream =~ tr/1/F/;
print "0x$stream\n";

##</code><code>##

0x0000
0x000F
0x00F0
0x00FF
0x0F00
0x0F0F
0x0FF0
0x0FFF
0xF000
0xF00F
0xF0F0
0xF0FF
0xFF00
0xFF0F
0xFFF0
0xFFFF