anchor.diff:  function VerifyZip(Strm : TStream) : TAbArchiveType;
   { determine if stream appears to be in PkZip format }
   var
  -  Footer       : TAbZipDirectoryFileFooter;
  +  Footer       : TAbZipEndOfCentralDirectoryRecord;
     Sig          : LongInt;
     TailPosition : int64;
     StartPos     : int64;
  
positive.code:   Result := aStream.Seek(-sizeof(TailRec), soEnd);
    if (Result >= 0) then begin
      aStream.ReadBuffer(TailRec, sizeof(TailRec));
      if (TailRec.trSig = Ab_ZipEndCentralDirectorySignature) and
         (TailRec.trLen = 0) then begin
        aStream.Seek(Result, soBeginning);
        Exit;
      end;
  
negative.code: 
          {if it's as valid a tail as we can check here...}
          CommentLen := -Offset - (TestPos - Buffer + sizeof(TailRec));
          if (TailRec.CommentLength <= CommentLen) then begin
  
            {calculate its position and exit}
            Result := Result + (TestPos - Buffer);
  