sub shrink {
    my $shrunk = "\0" x (length($_[0]) * 7/8);
    my $bit = 0;
    for my $orig_bit (0..(8*length($_[0])-1)) {
	next if $orig_bit % 8 == 7;
	vec($shrunk, $bit++, 1) = vec($_[0], $orig_bit, 1);
    }
    $shrunk;
}

sub grow {
    my $grown = "\0" x (length($_[0]) * 8/7);
    my $orig_bit = 0;
    for my $bit (0..(8*length($_[0])-1)) {
	vec($grown, $orig_bit++, 1) = vec($_[0], $bit, 1);
	vec($grown, $orig_bit++, 1) = 0 if $orig_bit % 8 == 7;
    }
    $grown;
}