/* construct this from x - but set to O if not on curve */
public ECP2(FP2 ix)
{
x = new FP2(ix);
y = new FP2(1);
z = new FP2(1);
FP2 rhs = RHS(x);
if (rhs.sqrt())
{
y.copy(rhs);
INF = false;
}
else
{
x.zero();
INF = true;
}
}