function extsearch( pat: PATTERN ): integer;

     var offs, i, m, nb, nr: integer;
         buff: TEXT;
         found: boolean;

         function fillbuff: integer;
         var j: integer;
         begin
            j := nb+1;
            while (j <= BUFSIZ-nb) and not eof(input) do begin
                read(buff[j]);  j := j+1; end;
            fillbuff := j-nb-1;
            for i:=j to BUFSIZ do buff[i] := chr(0);
         end;

     begin
       found := FALSE;
       m := length(pat);
       if m = 0 then begin
            extsearch := 1;
            found := TRUE;
            end;
       if m >= BUFSIZ then begin {*** Buffer is too small ***}
            extsearch := -1;
            found := TRUE;
            end;
       {*** Assume that the file is open and positioned ***}
       offs := 0;      {*** number of characters already read ***}
       nb := 0;        {*** number of characters in buffer ***}
       while not found do begin
          if nb >= m then begin
               {*** try to match ***}
               i := search(pat,buff);
               if i <> 0 then begin
                    extsearch := i+offs; {*** found ***}
                    found := TRUE;
                    end;
               for i:=1 to m-1 do buff[i] := buff[i+nb-m+2];
               offs := offs + nb-m+1;
               nb := m-1;
               end;
          {*** read more text ***}
          if not found then begin
               nr := fillbuff; 
               if nr <= 0 then begin
                    extsearch := 0; {*** not found ***}
                    found := TRUE;
                    end;
               nb := nb + nr;
               end;
          end;
    end;