return arm64.REG_R0 + n, true
		}
	case "V":
		if 0 <= n && n <= 31 {
			return arm64.REG_V0 + n, true
		}
	}
	return 0, false
}

// ARM64RegisterShift constructs an ARM64 register with shift operation.
func ARM64RegisterShift(reg, op, count int16) (int64, error) {
	// the base register of shift operations must be general register.
	if reg > arm64.REG_R31 || reg < arm64.REG_R0 {

			}
			count = int16((x & 31) << 7)
		}
	default:
		p.errorf("unexpected %s in register shift", tok.String())
	}
	if p.arch.Family == sys.ARM64 {
		off, err := arch.ARM64RegisterShift(r1, op, count)
		if err != nil {
			p.errorf("%v", err)
		}
		return off
	} else {
		return int64((r1 & 15) | op<<5 | count)
	}
}