my %charmap = (
    A => '00',
    C => '01',
    G => '10',
    T => '11',
);

my %digmap = (
    '00'    => "A",
    '01'    => "C",
    '10'    => "G",
    '11'    => "T",
);

my $string = $ARGV[0] ||  'GATTACCCC';
$string =~ s/(.)/$charmap{$1}/ge;


my $compressed = pack 'b*', $string;

print "COMP: $compressed\n";
printf "%d bytes\n", length
$compressed;

my @data;
push @data, $compressed;

# now use vec() to get at the single
# parts of $compressed

my $decompressed = unpack 'b*', $compressed;
$decompressed =~ s/(..)/$digmap{$1}/ge;
print "$decompressed\n";