my %tr;
  sub normalise { 
    my $s = shift;
    my $from = substr $s, 0, 4;
    my $tr = $tr{$from} ||= eval qq{ sub { tr{$from}{1234} } };
    &$tr for $s; 
    $s;
  } 

##</code><code>##

  $count = () = ($s =~ /[$search]/g)

##</code><code>##

  $count = ($s ^ ($search x length $s)) =~ tr/\0/\0/