【模板】【计几】判断点是否在凸包内

bool is_in(Point p,Point ch [],int n){
    //n>=2 
    int a = 1,b = n-1,c;
    if(cross(ch[0],ch[a],ch[b]) > 0) swap(a,b);
    // is_in allow on edge -> if( cross() > 0 || cross() < 0 )
    if( cross(ch[0],ch[a],p) >= 0 || cross(ch[0],ch[b],p) <= 0 ) return 0;
    while( abs(a-b) > 1){
        c = (a+b)/2;
        if( cross(ch[0],ch[c],p) > 0) b = c;
        else a = c;
    }
    //is_in allow on edge -> return cross() <= 0
    return cross(ch[a],ch[b],p) < 0;
}