module fouradder(A,B,cin,S,cout);   //四位超前進(jìn)位加法器模塊
 input[3:0] A,B;
 input cin;
 output[3:0] S;
 output cout;
 wire [3:0] G,P,S;
 wire [2:0] C;
 assign G=A&B;
 assign  P=A|B;
 assign  S[0]=P[0]&~G[0]^cin;
 assign  C[0]=G[0]|P[0]&cin;
 assign  S[1]=P[1]&~G[1]^C[0];
 assign  C[1]=G[1]|P[1]&C[0];
 assign  S[2]=P[2]&(~G[2])^C[1];
 assign  C[2]=G[2]|P[2]&C[1];
 assign  S[3]=P[3]&~G[3]^C[2];
 assign  cout=G[3]|P[3]&C[2];
endmodule