nonzero |= nonzero >> 4
	nonzero |= nonzero >> 2
	nonzero |= nonzero >> 1
	return int(^nonzero) & 1
}

// nonAdjacentForm computes a width-w non-adjacent form for this scalar.
//
// w must be between 2 and 8, or nonAdjacentForm will panic.
func (s *Scalar) nonAdjacentForm(w uint) [256]int8 {
	// This implementation is adapted from the one
	// in curve25519-dalek and is documented there: