Carry Skip Adder

Verilog code:
module carry_skip(output s, cout, input a, b, c0);
  wire w0, w1, w2;
  xor (w0, a, b);
  xor (s, w0, c0);
  and (w1, w0, c0);
  and (w2, a, b);
  or (cout, w1, w2);
endmodule
// Ripple Carry Adder - 4 bits
module RCA4(output reg[3:0] s, output reg cout, input [3:0] a, b, input c0);
  reg [3:1] c;
    carry_skip fa0(s[0], c[1], a[0], b[0], c0);
    carry_skip fa1(s[1], c[2], a[1], b[1], c[1]);
    carry_skip fa2(s[2], c[3], a[2], b[2], c[2]);
    carry_skip fa3(s[3], cout, a[3], b[3], c[3]);
endmodule
module SkipLogic(output c0_next, input [3:0] a, b, input c0, cout);
  wire p0, p1, p2, p3, P, e;
  or (p0, a[0], b[0]);
  or (p1, a[1], b[1]);
  or (p2, a[2], b[2]);
  or (p3, a[3], b[3]);
  and (P, p0, p1, p2, p3);
  and (e, P, c0);
  or (c0_next, e, cout);
endmodule


Testbench code:
module skip_tb();
  // Inputs
  reg [3:0] a;
  reg [3:0] b;
  reg c0;
  // Outputs
  wire [3:0] s;
  wire cout;
  // Instantiate the module under test
  SkipLogic dut(
    .s(s),
    .cout(cout),
    .a(a),
    .b(b),
    .c0(c0)
  );
  // Stimulus
  initial begin
    // Initialize inputs
    a = 4'b0000;
    b = 4'b0000;
    c0 = 0;
    // Test case 1: Inputs all zeros
    #10;
    // Test case 2: Inputs all ones
    a = 4'b1111;
    b = 4'b1111;
    c0 = 0;
    #10;
    
    // Test case 3: Carry in set to 1
    a = 4'b1010;
    b = 4'b0110;
    c0 = 1;
    #10;
    $finish;
    end
endmodule