module ksa4(input [3:0]a,
input [3:0]b,
input cin,
output [3:0]sum,

output carryout
    );
wire [3:0] p,g,cp,cg,ccg,ccp,c;

assign p=a^b;
assign g=a&b;

assign cg[0]=(g[0]);
assign cp[0]=(p[0]);

assign cg[1]=(p[1]&g[0])|g[1];
assign cp[1]=(p[1]&p[0]);

assign cg[2]=(p[2]&g[1])|g[2];
assign cp[2]=p[2]&p[1];

assign cg[3]=(p[3]&g[2])|g[3];
assign cp[3]=p[3]&p[2];

assign ccg[0]=cg[0];
assign ccp[0]=cp[0];

assign ccg[1]=cg[1];
assign ccp[1]=cp[1];

assign ccg[2]=(cp[2]&cg[0])|cg[2];
assign ccp[2]=cp[2]&cp[0];

assign ccg[3]=(cp[3]&cg[1])|cg[3];
assign ccp[3]=cp[3]&cp[1];

assign c=ccg;
assign sum[0]=p[0]^cin;
assign sum[1]=p[1]^c[0];
assign sum[2]=p[2]^c[1];
assign sum[3]=p[3]^c[2];
assign carryout=c[3];


endmodule

module test();
    reg[3:0] a,b;
    reg cin;
    wire[3:0] sum;
    wire carryout;

    ksa4 TestowanySumator(a, b, cin, sum, carryout);

    initial begin
        a=1111; b=1111; cin=0;
    end

    initial begin
        $display ("czas |  a + b + cin = sum i carryout");
        $monitor ($time, " | %d + %d + %d = %d i c_out = %b", a, b, cin, sum, carryout);
    end

endmodule //