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function FilesAreEqual(const File1, File2: TFileName): Boolean;
const
  BlockSize = 65536;
var
  fs1, fs2: TFileStream;
  L1, L2: Integer;
  B1, B2: array[1..BlockSize] of Byte;
begin
  Result := False;   
  fs1 := TFileStream.Create(File1, fmOpenRead or fmShareDenyWrite);
  try     
    fs2 := TFileStream.Create(File2, fmOpenRead or fmShareDenyWrite);
    try       
      if fs1.Size = fs2.Size then
      begin
        while fs1.Position < fs1.Size do
        begin
          L1 := fs1.Read(B1[1], BlockSize);
          L2 := fs2.Read(B2[1], BlockSize);
          if L1 <> L2 then
          begin
            Exit;
          end;
          if not CompareMem(@B1[1], @B2[1], L1) then Exit;
        end;
        Result := True;
      end;
    finally
      fs2.Free;
    end;
  finally
    fs1.Free;
  end;
end;