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if there are no bytes with the 8th bit set then
   there's no problem -- nevermind
...
          the original data is almost certainly utf8
      else
          the original data is definitely Latin1

if any bytes match /[\x80-\x9f]/ then
    it's pretty sure not to be Latin1

   eval "\$_ = decode('utf8',\$orig_data,Encode::FB_CROAK)";
   if ($@) {
      # it's not utf8, and so must be iso-8859-1
   }