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   if(defined($o)) {
    $o=substr(pack("N",$o | ($t{$string}<<12)),1,3);
...
   } else {
    $o=$t{$string};
   }

 $r=read(F1, $double, 3); ($double)=unpack(N,"\000$double");
 $old_code=$double & 0xfff; $double >>= 12;