}
			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_2D & 15) << 5)
		case "Q1":
			if isIndex {
				return errors.New("invalid register extension")
			}
			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_1Q & 15) << 5)
		case "B":
			if !isIndex {
				return nil
			}
			a.Reg = arm64.REG_ELEM + (reg & 31) + ((arm64.ARNG_B & 15) << 5)
			a.Index = num
		case "H":
			if !isIndex {
				return nil
			}