isIndex := false
	num := int16(0)
	isAmount := true // Amount is zero by default
	ext := ""
	if p.peek() == lex.LSH {
		// (Rn)(Rm<<2), the shifted offset register.
		ext = "LSL"
	} else {
		// (Rn)(Rm.UXTW<1), the extended offset register.
		// Rm.UXTW<<3, the extended register.
		p.get('.')
		tok := p.next()
		ext = tok.String()
	}
	if p.peek() == lex.LSH {

func ARM64RegisterExtension(a *obj.Addr, ext string, reg, num int16, isAmount, isIndex bool) error {
	Rnum := (reg & 31) + int16(num<<5)
	if isAmount {
		if num < 0 || num > 7 {
			return errors.New("index shift amount is out of range")
		}
	}
	if reg <= arm64.REG_R31 && reg >= arm64.REG_R0 {
		if !isAmount {
			return errors.New("invalid register extension")
		}
		switch ext {
		case "UXTB":