p521FromBytes((*p521UntypedFieldElement)(&tmp), &in)
	p521ToMontgomery(&e.x, &tmp)
	return e, nil
}

// Add sets e = t1 + t2, and returns e.
func (e *P521Element) Add(t1, t2 *P521Element) *P521Element {
	p521Add(&e.x, &t1.x, &t2.x)
	return e
}

// Sub sets e = t1 - t2, and returns e.
func (e *P521Element) Sub(t1, t2 *P521Element) *P521Element {
	p521Sub(&e.x, &t1.x, &t2.x)
	return e
}

	out1[7] = x1015
	out1[8] = x1016
}

// p521Add adds two field elements in the Montgomery domain.
//
// Preconditions:
//
//	0 ≤ eval arg1 < m
//	0 ≤ eval arg2 < m
//
// Postconditions:
//
//	eval (from_montgomery out1) mod m = (eval (from_montgomery arg1) + eval (from_montgomery arg2)) mod m
//	0 ≤ eval out1 < m