__enc_swreg
#define reg_both(x) __enc_swreg((x), NN_REG_GPR_BOTH)
#define reg_a(x) __enc_swreg((x), NN_REG_GPR_A)
#define reg_b(x) __enc_swreg((x), NN_REG_GPR_B)
#define reg_nnr(x) __enc_swreg((x), NN_REG_NNR)
#define reg_xfer(x) __enc_swreg((x), NN_REG_XFER)
#define reg_imm(x) __enc_swreg((x), NN_REG_IMM)
#define reg_none() __enc_swreg(0, NN_REG_NONE)