Function angle

code/geometry/primitives.cpp:20–21

bool collinear(P(a), P(b), P(c)) {
  return abs(ccw(a, b, c)) < EPS; }
double angle(P(a), P(b), P(c)) {
  return acos(dot(b - a, c - b) / abs(b - a) / abs(c - b)); }
double signed_angle(P(a), P(b), P(c)) {
  return asin(cross(b - a, c - b) / abs(b - a) / abs(c - b)); }
double angle(P(p)) { return atan2(imag(p), real(p)); }