my @masks = qw( 11011010101101010101010101101010
                10110110011011001100110011011001
                01110001111000111100001111000111
                00001111111000000011111111000000
                00000000000111111111111111000000
                00000000000000000000000000111111
                11111111111111111111111111111111 );
sub ecc {
    my ($hex) = @_;
    my $d = unpack 'B32', pack 'H8', $hex;
    my @r;
    push @r, unpack '%1B*', $_ & $d for @masks;
    $r[-1] = unpack '%1B*', $r[-1] . join "", @r[ 0 .. $#r - 1 ];
    return join "", @r
}