my @masks = qw( 01010110101010101010110101011011
                10011011001100110011011001101101
                11100011110000111100011110001110
                00000011111111000000011111110000
                00000011111111111111100000000000
                11111100000000000000000000000000
                11111111111111111111111111111111 );
sub ecc {
    my ($hex) = @_;
    my $d = unpack 'B32', pack 'H8', $hex;
    my @r;
    unshift @r, unpack '%1B*', $_ & $d for @masks;
    $r[0] = unpack '%1B*', $r[0] . join "", @r[ 1 .. $#r ];
    return join "", @r
}