Segment and Line Intersection

Point lineIntersection(Line l1, Line l2) {
    double z = l1.a * l2.b - l2.a * l1.b;
    if (!z) {
        return Point(-INF, -INF);
    }
    Point ans;
    ans.y = (-l1.a * l2.c + l2.a * l1.c) / z;
    ans.x = (l1.b * l2.c - l2.b * l1.c) / z;
    return ans;
}

Segment segmentIntersection(Segment s1, Segment s2) {
    Vector v1(s1.a, s1.b), v2(s1.a, s2.a), v3(s1.a, s2.b);
    Vector v4(s2.a, s2.b), v5(s2.a, s1.a), v6(s2.a, s1.b);
    Segment ans;
    if (s1.a == s1.b || s2.a == s2.b) {
        //S1 OR S2 IS A POINT
        if (s1.a == s1.b && s2.a == s2.b) {
            if (s1.a == s2.a)
                ans.a = ans.b = s1.a;
            else
                ans.a.x = -INF, ans.a.y = -INF;
        }
        else {
            if (s1.a == s1.b) swap(s1, s2);
            Point p = s2.a;
            Vector v1(p, s1.a), v2(p, s1.b);
            if (dotProduct(v1, v2) <= 0 && crossProduct(v1, v2) == 0)
                ans.a = ans.b = p;
            else
                ans.a.x = -INF, ans.a.y = -INF;
        }
        return ans;
    }
    if (crossProduct(v1, v2) == 0 && crossProduct(v1, v3) == 0) {
        //S1 AND S2 ARE COLINEAL
        bool flag = 0;
        if (s1.a.x == s1.b.x && s2.a.x == s2.b.x) {
            swap(s1.a.x, s1.a.y);
            swap(s1.b.x, s1.b.y);
            swap(s2.a.x, s2.a.y);
            swap(s2.b.x, s2.b.y);
            flag = 1;
        }
        if (s1.a.x > s1.b.x) swap(s1.a, s1.b);
        if (s2.a.x > s2.b.x) swap(s2.a, s2.b);
        if (s1.a.x > s2.a.x) swap(s1, s2);
        if (s1.a.x <= s2.a.x && s2.a.x <= s1.b.x) {
            ans.a = s2.a;
            if (s1.b.x < s2.b.x) ans.b = s1.b;
            else ans.b = s2.b;
            if (flag) {
                swap(ans.a.x, ans.a.y);
                swap(ans.b.x, ans.b.y);
            }
            return ans;
        }
    }
    if ((crossProduct(v1, v2) * crossProduct(v1, v3) > 0) || (crossProduct(v4, v5) * crossProduct(v4, v6) > 0)) {
        //S1 AND S2 DONT INTERSECT`
        ans.a.x = -INF, ans.a.y = -INF;
        return ans;
    }
    Line l1(s1.a, s1.b), l2(s2.a, s2.b);
    ans.a = ans.b = lineIntersection(l1, l2);
    return ans;
}