// add4pg.e  4 bits of adder that outputs P and G

// 4 bit stage with 9 inputs and 6 outputs
define add4pg(a[4], b[4], cin, s[4], pout, gout)
signal c0, c1, c2;
signal nc1;
signal p0, p1, p2, p3;
signal g0, g1, g2, g3;
circuits
  // basic four stages
  s00 use fadd(a[0], b[0], cin, s[0], c0);
  s01 use fadd(a[1], b[1], c0,  s[1], c1);
  s02 use fadd(a[2], b[2], c1,  s[2], c2);
  s03 use fadd(a[3], b[3], c2,  s[3], nc1);

  // Propegate and Generate terms and outputs 
  p0 <= a[0]|b[0] after 1ns;
  p1 <= a[1]|b[1] after 1ns;
  p2 <= a[2]|b[2] after 1ns;
  p3 <= a[3]|b[3] after 1ns;
  g0 <= a[0]&b[0] after 1ns;
  g1 <= a[1]&b[1] after 1ns;
  g2 <= a[2]&b[2] after 1ns;
  g3 <= a[3]&b[3] after 1ns;
  pout <= p3&p2&p1&p0 after 1ns;
  gout <= (g3)|                    // this would be cout for a ripple adder
          (p3&g2)|
          (p3&p2&g1)|
          (p3&p2&p1&g0)|
          (p3&p2&p1&p0&cin) after 1ns;
end circuits;
end add4pg;