module alu_4b (iS,iP,iQ,iF,oF,oY);
input[1:0] iS;
input[3:0] iP,iQ,iF;
output[3:0] oF,oY;
wire[3:0] oY;
wire iC, iB, oC,oB;

wire[3:0] tA0, tA1;
wire[3:0] tL0, tL1;

add_4b a_add (iC,iP,iQ,oC,tA0);
sub_4b a_sub (iB,iP,iQ,oB,tA1);
and_4b l_and (iP,iQ,tL0);
or_4b l_or (iP,iQ,tL1);

// separate flag bits for borrow and carry
assign oF = { 2'b00 , oB, oC };
// should get from same bit position
assign iB = iF[1];
assign iC = iF[0];

dmux41 sel0 (iS,tA0,tA1,tL0,tL1,oY);

endmodule