-- S.MG, 2018

package body SMG_Keccak is

  function Theta(Input : in State) return State is
    Output : State;
    C      : Plane;
    W      : ZWord;
  begin
    for X in XYCoord loop
      C(X) := Input(X, 0);
      for Y in 1..XYCoord'Last loop
        C(X) := C(X) xor Input(X, Y);
      end loop;
    end loop;

    for X in XYCoord loop
      W := C(X-1) xor Rotate_Left(C(X+1), 1);
      for Y in XYCoord loop
        Output(X,Y) := Input(X,Y) xor W;
      end loop;
    end loop;

    return Output;
  end Theta;

  function Rho(Input : in State) return State is
    Output      : State;
    X, Y, Old_Y : XYCoord;
  begin
    Output(0,0) := Input(0,0);
    X           := 1;
    Y           := 0;

    for T in 0..23 loop
      Output(X, Y) := Rotate_Left(Input(X,Y), ((T+1)*(T+2)/2) mod Z_Length);
      Old_Y := Y;
      Y := 2*X + 3*Y;
      X := Old_Y;
    end loop;
    return Output;
  end rho;

  function Pi(Input : in State) return State is
    Output: State;
  begin
    for X in XYCoord loop
      for Y in XYCoord loop
        Output(Y, 2*X + 3*Y) := Input(X, Y);
      end loop;
    end loop;
    return Output;
  end pi;

  function Chi(Input : in State) return State is
    Output: State;
  begin
    for Y in XYCoord loop
      for X in XYCoord loop
        Output(X, Y) := Input(X, Y) xor 
                        ( (not Input(X + 1, Y)) and Input(X + 2, Y) );
      end loop;
    end loop;
    return Output;
  end chi;

  function Iota(Round_Const : in ZWord; Input : in State) return State is
    Output: State;
  begin
    Output := Input;
    Output(0,0) := Input(0,0) xor Round_Const;
    return Output;
  end iota;

  function Keccak_Function(Input: in State) return State is
    Output: State;
  begin
    Output := Input;
    for I in Round_Index loop
      Output := Iota(RC(I), Chi(Pi(Rho(Theta(Output)))));
    end loop;

    return Output;
  end Keccak_Function;

end SMG_Keccak;