This has constant overhead by expanding only 8 chars at a time. 
sub shrink {
    my $packed = '';
    while ($_[0] =~ /(.{1,8})/gs) {
        my $bitstr = unpack('B*', $1);
        $bitstr =~ s/.(.{7})/$1/g;
        $packed .= pack('B*', $bitstr);
    }
    $packed;
}

sub grow {
    my $unpacked = '';
    while ($_[0] =~ /(.{1,7})/gs) {
        my $bitstr = unpack('B*', $1);
        $bitstr =~ s/(.{7})/0$1/g;
        $unpacked .= pack('B*', $bitstr);
    }
    $unpacked;
}

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Caution: Contents may have been coded under pressure.

In reply to Re^3: Efficient 7bit compression by Roy Johnson
in thread Efficient 7bit compression by Limbic~Region

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