sub score {
  my ( $bd, $hi, $pos, $old, $word ) = @_;
  my $len  = length $word;
  my $mask = ( $old ^ $word ) =~ tr/\0/\xff/cr;
  say "in score pos old word";
  say "$pos, $old, $word";
         my( $hex ) = unpack( 'H*', $mask );
       print "score mask s $hex\n"; ;
  my $helper = ( $old & ~$mask ) =~ tr/\0/-/r;
  say "helper is $helper";
say "$bd";