my @CONV = glob( "{T,C,A,G}" x 4 );
my $dna = join "", @CONV[ unpack "C*", $raw ];

##</code><code>##

## takes 16 bits (= 8 bases = unsigned short) at a time
my @CONV = glob( "{T,C,A,G}" x 8 );
my $dna = join "", @CONV[ unpack "S*", $raw ];

##</code><code>##

substr($dna, $_, $mblock{$_}, lc(substr($dna, $_, $mblock{$_})))

##</code><code>##

substr($dna, $_, $mblock{$_}) ^= (" " x $mblock{$_});