On the encoding side, it is only slightly harder to build the bit vector directly, using vec() instead of pack 'b'.

sub huff1 {
    my ( $string, $codes) = @_;

    my ( $ret, $len) = ( '', 0); # $len counts bits
    for ( split( //, $string), '_eos' ) {
        vec( $ret, $len ++, 1) = $_ for split //, $codes->{ $_};
    }
    return $ret;
}
[download]

Update: No, it isn't. Dehuff is as easily adapted to vec().

sub dehuff1 {
    my ( $string, $code) = @_;
    my %decode = reverse %$code;
    my ( $ret, $c, $where) = ( '', '', 0);
    while ( 1 ) {
        $c .= vec( $string, $where ++, 1);
        next unless exists $decode{ $c};
        last if $decode{ $c} eq '_eos';
        $ret .= $decode{ $c};
        $c = '';
    }
    return $ret;
}
[download]

Anno