C++ function which tests whether two lines are intersected

intersection.cpp

int intersection(Point2i p1, Point2i p2, Point2i p3, Point2i p4) {
    // Store the values for fast access and easy
    // equations-to-code conversion
    int x1 = p1.x, x2 = p2.x, x3 = p3.x, x4 = p4.x;
    int y1 = p1.y, y2 = p2.y, y3 = p3.y, y4 = p4.y;
     
    int d = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);
    // If d is zero, there is no intersection
    if (d == 0) return 0;
     
    // Get the x and y
    int pre = (x1*y2 - y1*x2);
    int post = (x3*y4 - y3*x4);
    float x = ( pre * (x3 - x4) - (x1 - x2) * post ) / d;
    float y = ( pre * (y3 - y4) - (y1 - y2) * post ) / d;
     
    // Check if the x and y coordinates are within both lines
    if ( x < min(x1, x2) || x > max(x1, x2) || x < min(x3, x4) || x > max(x3, x4) ) return 0;
    if ( y < min(y1, y2) || y > max(y1, y2) || y < min(y3, y4) || y > max(y3, y4) ) return 0;

    int td = (x1 - x2) * (y4 - y1) + (y1 - y2) * (x1 - x4);
    if ( td > 0 ) return 1;
    if ( td < 0 ) return -1;

    // Return the point of intersection
    // Point2f* ret = new Point2f();
    // ret.x=x;
    // ret.y=y;
    // return ret;
}