for my $i (0..20) {
    vec( $bitstring, $offset++, 4 ) = $i ;
}

##</code><code>##

my $bits = unpack("A4*", $bitstring);

##</code><code>##

print unpack("b*",$bitstring);

##</code><code>##

0000100001001100001010
1001101110000110010101
1101001110110111111100
0010000100110000100000

##</code><code>##

print unpack("h*",$bitstring);

##</code><code>##

0123456789abcdef012340