adder_4_bit.v

一个超前进位加法器（及其testbench) .v文件

module adder_4_bit(a,b,cin,s,cout);
input [3:0] a, b;
input cin;
output [3:0] s;
output cout;

wire [3:0] p, g, c;

assign   p[0] = a[0] ^ b[0],
    p[1] = a[1] ^ b[1],
    p[2] = a[2] ^ b[2],
    p[3] = a[3] ^ b[3];
assign   g[0] = a[0] & b[0],
   g[1] = a[1] & b[1],
   g[2] = a[2] & b[2],
   g[3] = a[3] & b[3];
assign 	c[0] = g[0] | (p[0] & cin),
	c[1] = g[1] | (p[1] & g[0]) | (p[1] & p[0] & cin),
	c[2] = g[2] | (p[2] & g[1]) | (p[2] & p[1] & p[0] & cin) ,
	c[3] = g[3] | (p[3] & g[2]) | (p[3] & p[2] & g[1]) & (p[3] & p[2] & p[1] & p[0] & cin);
assign	s[0] = p[0] ^ cin,
	s[1] = p[1] ^ c[0],
	s[2] = p[2] ^ c[1],
	s[3] = p[3] ^ c[2];
assign	cout = c[3];
endmodule