go =>
   foreach(I in 0..2**5-1)
      G = gray_encode1(I),
      E = gray_decode1(G),
      printf("%2d %6w %2d %6w %6w %2d\n",I,I.to_binary_string,
                                         G, G.to_binary_string,
                                         E.to_binary_string, E)
   end,
   nl,
   println("Checking 2**1300:"),
   N2=2**1300,
   G2=gray_encode1(N2),
   E2=gray_decode1(G2),
   % println(g2=G2),
   % println(e2=E2),
   println(check=cond(N2==E2,same,not_same)),
   nl.

gray_encode1(N) = N ^ (N >> 1).
gray_decode1(N) = P =>
    P = N,
    N := N >> 1,
    while (N != 0)
      P := P ^ N,
      N := N >> 1
    end.