Re: [Qemu-devel] [PATCH] 2/4] target-ppc: Implement bcdctn. instruction

[joserz@linux.vnet.ibm.com]

On Thu, Oct 27, 2016 at 12:20:17PM +1100, David Gibson wrote:
> On Wed, Oct 26, 2016 at 11:18:56AM -0200, Jose Ricardo Ziviani wrote:
> > bcdctn. converts from BCD to National numeric format. National format
> > uses a byte to represent a digit where the most significant nibble is
> > always 0x3 and the least sign. nibbles is the digit itself.
> > 
> > Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> > ---
> >  target-ppc/helper.h                 |  1 +
> >  target-ppc/int_helper.c             | 46 +++++++++++++++++++++++++++++++++++++
> >  target-ppc/translate/vmx-impl.inc.c | 24 ++++++++++++++++++-
> >  3 files changed, 70 insertions(+), 1 deletion(-)
> > 
> > diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> > index d30ec60..92eaaf0 100644
> > --- a/target-ppc/helper.h
> > +++ b/target-ppc/helper.h
> > @@ -370,6 +370,7 @@ DEF_HELPER_4(vpermxor, void, avr, avr, avr, avr)
> >  DEF_HELPER_4(bcdadd, i32, avr, avr, avr, i32)
> >  DEF_HELPER_4(bcdsub, i32, avr, avr, avr, i32)
> >  DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
> > +DEF_HELPER_2(bcdctn, i32, avr, avr)
> >  
> >  DEF_HELPER_2(xsadddp, void, env, i32)
> >  DEF_HELPER_2(xssubdp, void, env, i32)
> > diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> > index 494c74e..cffe82c 100644
> > --- a/target-ppc/int_helper.c
> > +++ b/target-ppc/int_helper.c
> > @@ -2494,6 +2494,17 @@ static uint8_t get_national_digit(ppc_avr_t *reg, int n)
> >  #endif
> >  }
> >  
> > +static void set_national_digit(ppc_avr_t *reg, uint8_t val, int n)
> > +{
> > +#if defined(HOST_WORDS_BIGENDIAN)
> > +    reg->u16[8 - n] &= 0;
> > +    reg->u16[8 - n] |= val;
> 
> The &= always sets the value to 0, so you might as well just use a
> plain assignment in place of the &=, |=.

OK! I'll fix it in v2.

> 
> > +#else
> > +    reg->u16[n] &= 0;
> > +    reg->u16[n] |= val;
> > +#endif
> > +}
> > +
> >  static int bcd_cmp_mag(ppc_avr_t *a, ppc_avr_t *b)
> >  {
> >      int i;
> > @@ -2667,6 +2678,41 @@ uint32_t helper_bcdcfn(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> >      return cr;
> >  }
> >  
> > +uint32_t helper_bcdctn(ppc_avr_t *r, ppc_avr_t *b)
> > +{
> > +    int i;
> > +    int cr = 0;
> > +    int invalid = 0;
> > +    int sgnb = bcd_get_sgn(b);
> > +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> > +
> > +    int eq_flag = (b->u64[HI_IDX] == 0) && ((b->u64[LO_IDX] >> 4) == 0);
> > +    int ox_flag = (b->u64[HI_IDX] != 0) || ((b->u64[LO_IDX] >> 8) != 0);
> 
> This looks wrong.  You're shifing the low half right 8 bits ==  2
> nybbles == 1 digit + sign.  So this will set the overflow flag if your
> input is a number of >1 digit.  I think you want >>32, so it only sets
> overflow if the input exceeds 7 decimal digits + sign.

OK! I'll fix it in v2.

> 
> > +    for (i = 1; i < 8; i++) {
> > +        set_national_digit(&ret, 0x30 + bcd_get_digit(b, i, &invalid), i);
> > +    }
> > +    set_national_digit(&ret, (sgnb == -1) ? NATIONAL_NEG : NATIONAL_PLUS, 0);
> > +
> > +    if (!eq_flag) {
> > +        cr = (sgnb == -1) ? 1 << CRF_LT : 1 << CRF_GT;
> > +    } else {
> > +        cr = 1 << CRF_EQ;
> > +    }
> > +
> > +    if (ox_flag) {
> > +        cr |= 1 << CRF_SO;
> > +    }
> > +
> > +    if (unlikely(invalid)) {
> > +        cr = 1 << CRF_SO;
> > +    }
> > +
> > +    *r = ret;
> > +
> > +    return cr;
> > +}
> > +
> >  void helper_vsbox(ppc_avr_t *r, ppc_avr_t *a)
> >  {
> >      int i;
> > diff --git a/target-ppc/translate/vmx-impl.inc.c b/target-ppc/translate/vmx-impl.inc.c
> > index 2abdcac..4364881 100644
> > --- a/target-ppc/translate/vmx-impl.inc.c
> > +++ b/target-ppc/translate/vmx-impl.inc.c
> > @@ -894,9 +894,29 @@ static void gen_##op(DisasContext *ctx)             \
> >      tcg_temp_free_i32(ps);                          \
> >  }
> >  
> > +#define GEN_BCD3(op)                                \
> > +static void gen_##op(DisasContext *ctx)             \
> > +{                                                   \
> > +    TCGv_ptr rb, rd;                                \
> > +                                                    \
> > +    if (unlikely(!ctx->altivec_enabled)) {          \
> > +        gen_exception(ctx, POWERPC_EXCP_VPU);       \
> > +        return;                                     \
> > +    }                                               \
> > +                                                    \
> > +    rb = gen_avr_ptr(rB(ctx->opcode));              \
> > +    rd = gen_avr_ptr(rD(ctx->opcode));              \
> > +                                                    \
> > +    gen_helper_##op(cpu_crf[6], rd, rb);            \
> > +                                                    \
> > +    tcg_temp_free_ptr(rb);                          \
> > +    tcg_temp_free_ptr(rd);                          \
> > +}
> >  GEN_BCD(bcdadd)
> >  GEN_BCD(bcdsub)
> >  GEN_BCD2(bcdcfn)
> > +GEN_BCD3(bcdctn)
> >  
> >  static void gen_xpnd04_1(DisasContext *ctx)
> >  {
> > @@ -908,7 +928,8 @@ static void gen_xpnd04_1(DisasContext *ctx)
> >      case 4:
> >          break; /* bcdctz. */
> >      case 5:
> > -        break; /* bcdctn. */
> > +        gen_bcdctn(ctx);
> > +        break;
> >      case 6:
> >          break; /* bcdcfz. */
> >      case 7:
> 
> Uh.. doesn't adding bcdctn to this make it identical to gen_xpnd04_2?

Actually this opcode is invalid for bcdctn as per ISA3.0.

Do you think that I should throw something like a SIGILL for this particular case?

> 
> > @@ -1024,3 +1045,4 @@ GEN_VXFORM_DUAL(vsldoi, PPC_ALTIVEC, PPC_NONE,
> >  #undef GEN_VAFORM_PAIRED
> >  
> >  #undef GEN_BCD2
> > +#undef GEN_BCD3
> 
> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson