// add4.e  a simple 4 bit adder
//         this uses a built in component  fadd  a one bit adder

define fadd(a, b, cin, s, cout)
circuits
  s <= a ^ b ^ cin after 1ns;
  cout <= (a&b)|(a&cin)|(b&cin) after 1ns;
end circuits;
end fadd;

// add4.e  4 bit full adder component
// simple ripple carry adder
// inputs a, b, cin
// outputs sum, cout

define add4(a[4], b[4], cin, sum[4], cout)
  signal c[3];
circuits
  a0 use fadd(a[0], b[0], cin , sum[0], c[0]);
  a1 use fadd(a[1], b[1], c[0], sum[1], c[1]);
  a2 use fadd(a[2], b[2], c[1], sum[2], c[2]);
  a3 use fadd(a[3], b[3], c[2], sum[3], cout);
end circuits;
end add4;