module SB_LUT4(output O, input I0, I1, I2, I3);
  parameter [15:0] INIT = 0;
  wire [ 7: 0] s3 = I3 ? INIT[15: 8] : INIT[ 7: 0];
  wire [ 3: 0] s2 = I2 ?   s3[ 7: 4] :   s3[ 3: 0];
  wire [ 1: 0] s1 = I1 ?   s2[ 3: 2] :   s2[ 1: 0];
  assign O = I0 ? s1[1] : s1[0];
endmodule

module SB_DFF (output reg Q, input C, D);
  always @(posedge C)
    Q <= D;
endmodule