my @a = map ord, split //, "<your message here>";
my @b;
while(@a){
        $#a or unshift @b, @a and last;
        my $c = shift @a; # ($_+$&)/2;
        my $d = shift @a; # ($_-$&)/2;
        unshift @b, $c - $d; # $&
        push @a, $c + $d; # $_
}
unshift @b, undef;
$_ = join "+",@b;
s/\+-/-/g;
s/[3-9][0-9]/($&>=32&&$&!=43&&$&!=45&&$&<48||$&>=58?chr $&:$&)/eg;
s/1[0-2][0-9]/($&<127?chr $&:$&)/eg;
print "$_\n";