线段与线段的交点

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point getcrosspoint(point a,point a1,point b,point b1)
{
    point base=b1-b;
    double d1=abs(cross(base,a-b));
    double  d2=abs(cross(base,a1-b));
    double t=d1/(d1+d2);
    point temp=(a1-a)*t;
    return a+temp;
}