4.17三种方式ADD

module top;
wire A, B, Cin, E, F, G, cout, SUM;
system_clock #400 clock1(Cin);
system_clock #200 clock2(B);
system_clock #100 clock3(A);
and a1(E, A, B);
xor a2(F, A, B);
and a3(G, F, Cin);
or  a4(cout,E, G);
xor  a5(SUM, F, Cin);
endmodule
module system_clock(clk);
parameter PERIOD=100;
output clk;
reg clk;
initial clk=0;
always
 begin
#(PERIOD/2) clk=~clk;
 end
always@(posedge clk)
 if($time>1000)$stop;
endmodule




module top;
  integer ia,ib,ic;
  reg  a,b,cin;
  wire cout,sum;
  and_behavioral and1(cout,sum,a,b,cin);
  initial
    begin
      for (ia=0; ia<=1; ia = ia+1)
        begin
          a = ia;
          for (ib=0; ib<=1; ib = ib + 1)
            begin
              b = ib;
  for (ic=0; ic<=1; ic = ic + 1)
  begin
  cin=ic;
              #1 $display("a=%d b=%d cin=%d cout=%d sum=%d",a,b,cin,cout,sum);
                        end
    end
     end
end
endmodule
module and_behavioral(cout,sum,a,b,cin);
  input a,b,cin;
  output cout,sum;
  wire a,b,cin;
  reg cout,sum;
  always @(a or b or cin)
   begin
    cout  = a&cin|a&b|b&cin;
    sum = ~a&b&~cin|~cin&a&~b|a&b&cin|~a&~b&cin;
   end    
endmodule







module test_adder1;
 reg a,b;
 reg carry_in ;
 wire sum;
 wire carry_out;
 adder1_behavorial A1(carry_out, sum, a, b, carry_in);
 initial
  begin
    carry_in = 0; a = 0; b = 0;
    # 100 if ( carry_out != 0 | sum !== 0)
                $display(" 0+0+0=00 sum is WRONG!");
              else
                $display(" 0+0+0=00 sum is RIGHT!");
   carry_in = 0; a = 0; b = 1;
    # 100 if ( carry_out != 0 | sum !== 1)
                $display(" 0+0+1=01 sum is WRONG!");
              else
                $display(" 0+0+1=01 sum is RIGHT!");
    carry_in = 0; a = 1; b = 0;
    # 100 if ( carry_out != 0 | sum !== 1)
               $display(" 0+1+0=01 sum is WRONG!");
              else
               $display(" 0+1+0=01 sum is RIGHT!");
   carry_in = 0; a = 1; b = 1;
    # 100 if ( carry_out != 1 | sum !== 0)
               $display(" 0+1+1=10 sum is WRONG!");
              else
               $display(" 0+1+1=10 sum is RIGHT!");
   carry_in = 1; a = 0; b = 0;
    # 100 if ( carry_out != 0 | sum !== 1)
               $display(" 1+0+0=01 sum is WRONG!");
              else
               $display(" 1+0+0=01 sum is RIGHT!");
    carry_in = 1; a = 0; b = 1;
    # 100 if ( carry_out != 1 | sum !== 0)
               $display(" 1+0+1=10 sum is WRONG!");
              else
               $display(" 1+0+1=10 sum is RIGHT!");
    carry_in = 1; a = 1; b = 0;
    # 100 if ( carry_out != 1 | sum !== 0)
               $display(" 1+1+0=10 sum is WRONG!");
              else
               $display(" 1+1+0=10 sum is RIGHT!");
    carry_in = 1; a = 1; b = 1;
    # 100 if ( carry_out != 1 | sum !== 1)
               $display(" 1+1+1=11 sum is WRONG!");
              else
               $display(" 1+1+1=11 sum is RIGHT!");
    $finish;
  end
endmodule

module adder1_behavorial (carry_out, sum, a, b, carry_in);
 input a, b, carry_in;
 output carry_out, sum;
  assign sum = (~a&b&~carry_in)|(~carry_in&a&~b)|(a&b&carry_in)|(~a&~b&carry_in);
  assign carry_out = a&carry_in|a&b|b&carry_in;
endmodule