Method is_x_coord

test/functional/test_framework/key.py:98–101

Test whether x is a valid X coordinate on the curve.

(self, x)

        return z1 != 0 and (pow(x1, 3, self.p) + self.a * x1 * z4 + self.b * z2 * z4 - pow(y1, 2, self.p)) % self.p == 0

    def is_x_coord(self, x):
        """Test whether x is a valid X coordinate on the curve."""
        x_3 = pow(x, 3, self.p)
        return jacobi_symbol(x_3 + self.a * x + self.b, self.p) != -1

    def lift_x(self, x):
        """Given an X coordinate on the curve, return a corresponding affine point for which the Y coordinate is even."""