my (%b2c, %c2b);
$b2c{unpack 'b8', $_} = $_ for map chr, 0..255;
$c2b{$_} = unpack 'b7', $_ for map chr, 0..127;
    
sub packdevicegsm2 { # Device::Gsm::Pdu:encode_text7, not going via hex
    my @char = split //, shift;
    my($result, $bits);
    map { $bits .= $c2b{$_} } @char; 
    if (my $len = length($bits) % 8) { $bits .= '0' x (8 - $len) }
    $result .= $b2c{ substr $bits, 0, 8, '' } while length $bits;
    return chr(scalar @char) . $result;
}

sub unpackdevicegsm2 { # Device::Gsm::Pdu:decode_text7, not going via hex
    my $text7 = shift;
    my $len = ord substr( $text7, 0, 1, '' );
    my $bits = '';
    $bits .= unpack 'b8', substr $text7, 0, 1, '' while length $text7;
    my $decoded = '';
    $decoded .= pack 'b7', substr $bits, 0, 7, '' while length $bits >= 7;
    return substr $decoded, 0, $len;
}