carry_look_ahead_4bit.v

`timescale 1ns / 1ps
//carry look ahead adder of 4 bit
module carry_look_ahead_4bit(a,b, cin, sum,cout);
input [3:0] a,b;
input cin;
output [3:0] sum;
output cout;
wire [3:0] p,g,c;
xor(p[0],a[0],b[0]);    
xor(p[1],a[1],b[1]);
xor(p[2],a[2],b[2]);
xor(p[3],a[3],b[3]);
and(g[0],a[0],b[0]);
and(g[1],a[1],b[1]);
and(g[2],a[2],b[2]);
and(g[3],a[3],b[3]);
wire c1t1;
and(ct1,cin,p[0]);
or(c[0],ct1,g[0]);
wire c2t1,c2t2,c2t3,c2t4;
and(c2t1,p[0],p[1]);
and(c2t2,cin,c2t1);
and(c2t3,g[0],p[1]);
or(c2t4,c2t3,g[1]);
or(c[1],c2t4,c2t2);
wire c3t1,c3t2,c3t3,c3t4,c3t5,c3t6,c3t7;
and(c3t1,g[1],p[2]);
and(c3t2,p[1],p[2]);
and(c3t3,g[0],c3t2);
and(c3t4,p[0],c3t2);
and(c3t5,cin,c3t4);
or(c3t6,c3t1,g[2]); 
or(c3t7,c3t3,c3t6);
or(c[2],c3t5,c3t7);
wire c4t1,c4t2,c4t3,c4t4,c4t5,c4t6,c4t7,c4t8,c4t9,c4t10;
and(c4t1,g[2],p[3]);
and(c4t2,p[2],p[3]);
and(c4t3,g[1],c4t2);
and(c4t4,p[1],c4t2);
and(c4t5,g[0],c4t4);
and(c4t6,p[0],c4t4);
and(c4t7,cin,c4t6);
or(c4t8,g[3],c4t1);
or(c4t9,c4t3,c4t8);
or(c4t10,c4t9,c4t5);
or(c[3],c4t10,c4t7);
wire ts1,ts2,ts3,ts4;
xor(ts1,a[0],b[0]);
xor(sum[0],cin,ts1);
xor(ts2,a[1],b[1]);
xor(sum[1],c[0],ts2);
xor(ts3,a[2],b[2]);
xor(sum[2],c[1],ts3);
xor(ts4,a[3],b[3]);
xor(sum[3],c[2],ts4);
buf(cout,c[3]);
endmodule