Sorting angles

//sorting by angles of integer vectors
//nasarouf@cs.ubc.ca

#define X first
#define Y second
const double PI=(2*acos(0.0f));
typedef long long Long;
typedef pair<int,int> PII;
PII p[MAX],q[MAX];
int n;
#define LEN(a,b) ((Long)(a)*(a)+(Long)(b)*(b))

bool parallel(const PII& a, const PII &b){
    if ((Long)a.X*b.X<0) return false;
    if (a.X==0 && b.X==0) return ((Long)a.Y*b.Y>0);
    return ((Long)a.X*b.Y == (Long) a.Y*b.X);
}

int cmp(const void *pa, const void* pb){
    const PII *a=(const PII*)pa;
    const PII *b=(const PII*)pb;
    if (!parallel(*a, *b)){
        double A=atan2((double)a->second,(double)a->first), B=atan2((double)b->second,(double)b->first);
        if (A<0) A+=2*PI;
        if (B<0) B+=2*PI;
        if (A<B) return -1;
        return 1;
    }
    if (LEN(a->first,a->second)<LEN(b->first,b->second)) return -1;
    //if (LEN(a->first,a->second)>LEN(b->first,b->second)) return 1;
    //if ((Long)a->first*b->second==(Long)a->second*b->first) return 0;
    //return 0;
    return 1;
}

Long dot(PII& a, PII &b){
    return (Long)a.X*b.X+(Long)a.Y*b.Y;
}

//
//
qsort(q,n-1,sizeof(q[0]),cmp);