code: function fp_add(r, n1, n2, p, l) {
  	if (mpn_add(r, n1, n2, l) || mpn_cmp(r, p, l) >= 0) {
  		mpn_sub(r, r, p, l);
  	}
  	return r;
  }
docs: /*
  Adds two multi-precision integers n1 and n2 in the finite field of order p,
  stores their sum into r, and returns r.