+// Is point on curve?
+func (c *Curve) Contains(x, y *big.Int) bool {
+ r1 := big.NewInt(0)
+ r2 := big.NewInt(0)
+ r1.Mul(y, y)
+ r1.Mod(r1, c.P)
+ r2.Mul(x, x)
+ r2.Add(r2, c.A)
+ r2.Mul(r2, x)
+ r2.Add(r2, c.B)
+ r2.Mod(r2, c.P)
+ c.pos(r2)
+ return r1.Cmp(r2) == 0
+}
+
+// Get the size of the point's coordinate in bytes.
+// 32 for 256-bit curves, 64 for 512-bit ones.