case arg_Dd:
		return D0 + Reg(x&(1<<5-1))

	case arg_Dm:
		return D0 + Reg((x>>16)&(1<<5-1))

	case arg_Dn:
		return D0 + Reg((x>>5)&(1<<5-1))

	case arg_Hd:
		return H0 + Reg(x&(1<<5-1))

	case arg_Hn:
		return H0 + Reg((x>>5)&(1<<5-1))

	case arg_IAddSub:
		imm12 := (x >> 10) & (1<<12 - 1)
		shift := (x >> 22) & (1<<2 - 1)
		if shift > 1 {
			return nil
		}
		shift = shift * 12