Re: [Qemu-devel] [PATCH] 1/4] target-ppc: Implement bcdcfn. instruction

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Oct 26, 2016 at 11:18:55AM -0200, Jose Ricardo Ziviani wrote:
> bcdcfn. converts from National numeric format to BCD. 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             | 54 ++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c | 75 +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-ops.inc.c  |  4 +-
>  4 files changed, 132 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index 04c6421..d30ec60 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -369,6 +369,7 @@ 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(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 5aee0a8..494c74e 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -2417,6 +2417,8 @@ void helper_vsubecuq(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, ppc_avr_t *c)
>  #define BCD_NEG_PREF    0xD
>  #define BCD_NEG_ALT     0xB
>  #define BCD_PLUS_ALT_2  0xE
> +#define NATIONAL_PLUS   0x2B
> +#define NATIONAL_NEG    0x2D
>  
>  #if defined(HOST_WORDS_BIGENDIAN)
>  #define BCD_DIG_BYTE(n) (15 - (n/2))
> @@ -2483,6 +2485,15 @@ static void bcd_put_digit(ppc_avr_t *bcd, uint8_t digit, int n)
>      }
>  }
>  
> +static uint8_t get_national_digit(ppc_avr_t *reg, int n)
> +{
> +#if defined(HOST_WORDS_BIGENDIAN)
> +    return reg->u16[8 - n] & 0xFF;
> +#else
> +    return reg->u16[n] & 0xFF;
> +#endif

You're discarding the high byte of each digit here, which means you
won't detect badly encoded values that have correct low bytes.

> +}
> +
>  static int bcd_cmp_mag(ppc_avr_t *a, ppc_avr_t *b)
>  {
>      int i;
> @@ -2613,6 +2624,49 @@ uint32_t helper_bcdsub(ppc_avr_t *r,  ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
>      return helper_bcdadd(r, a, &bcopy, ps);
>  }
>  
> +uint32_t helper_bcdcfn(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> +{
> +    int i;
> +    int is_zero = 0;
> +    int cr = 0;
> +    int national = 0;
> +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> +    uint16_t sgnb = get_national_digit(b, 0);
> +    int invalid = (sgnb != NATIONAL_PLUS && sgnb != NATIONAL_NEG);
> +
> +    for (i = 1; i < 8; i++) {
> +        national = get_national_digit(b, i);
> +
> +        is_zero += (national == 0x30);
> +        if (unlikely(national < 0x30 || national > 0x39)) {
> +            invalid = 1;
> +        }
> +
> +        bcd_put_digit(&ret, national & 0xf, i);
> +    }
> +
> +    if (sgnb == NATIONAL_PLUS ||
> +            (b->u64[0] == 0 && b->u64[1] == 0)) {

The second part of this test doesn't seem to make much sense.  I think
you're trying to always put a positive sign on a zero result.  But
you're testing the national encoded input, not the BCD encoded output,
and zero will *not* be all zero bits in national encoding.

> +        bcd_put_digit(&ret, (ps == 0) ? BCD_PLUS_PREF_1 : BCD_PLUS_PREF_2, 0);
> +    } else {
> +        bcd_put_digit(&ret, BCD_NEG_PREF, 0);
> +    }
> +
> +    if (!is_zero) {

From the logic above, 'is_zero' is currently a count of how many 0
digits the value has, not whether the value as a whole is zero.  That
means you will get the wrong result here.

> +        cr = (sgnb == NATIONAL_PLUS) ? 1 << CRF_GT : 1 << CRF_LT;
> +    } else {
> +        cr = 1 << CRF_EQ;
> +    }
> +
> +    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 c8998f3..2abdcac 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -871,8 +871,81 @@ static void gen_##op(DisasContext *ctx)             \
>      tcg_temp_free_i32(ps);                          \
>  }
>  
> +#define GEN_BCD2(op)                                \
> +static void gen_##op(DisasContext *ctx)             \
> +{                                                   \
> +    TCGv_ptr rd, rb;                                \
> +    TCGv_i32 ps;                                    \
> +                                                    \
> +    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));              \
> +                                                    \
> +    ps = tcg_const_i32((ctx->opcode & 0x200) != 0); \
> +                                                    \
> +    gen_helper_##op(cpu_crf[6], rd, rb, ps);        \
> +                                                    \
> +    tcg_temp_free_ptr(rb);                          \
> +    tcg_temp_free_ptr(rd);                          \
> +    tcg_temp_free_i32(ps);                          \
> +}
> +
>  GEN_BCD(bcdadd)
>  GEN_BCD(bcdsub)
> +GEN_BCD2(bcdcfn)
> +
> +static void gen_xpnd04_1(DisasContext *ctx)
> +{
> +    switch (opc4(ctx->opcode)) {
> +    case 0:
> +        break; /* bcdctsq. */
> +    case 2:
> +        break; /* bcdcfsq. */
> +    case 4:
> +        break; /* bcdctz. */
> +    case 5:
> +        break; /* bcdctn. */
> +    case 6:
> +        break; /* bcdcfz. */
> +    case 7:
> +        gen_bcdcfn(ctx);
> +        break;
> +    case 31:
> +        break; /* bcdsetsgn. */
> +    default:
> +        break;
> +    }
> +}
> +
> +static void gen_xpnd04_2(DisasContext *ctx)
> +{
> +    switch (opc4(ctx->opcode)) {
> +    case 0:
> +        break; /* bcdctsq. */
> +    case 2:
> +        break; /* bcdcfsq. */
> +    case 4:
> +        break; /* bcdctz. */
> +    case 6:
> +        break; /* bcdcfz. */
> +    case 7:
> +        gen_bcdcfn(ctx);
> +        break;
> +    case 31:
> +        break; /* bcdsetsgn. */
> +    default:
> +        break;
> +    }
> +}

I thougt the main opcode table now had support for opc4, so you
shouldn't need these special expanders.

> +GEN_VXFORM_DUAL(vsubcuw, PPC_ALTIVEC, PPC_NONE, \
> +                xpnd04_1, PPC_NONE, PPC2_ISA300)
> +GEN_VXFORM_DUAL(vsubsws, PPC_ALTIVEC, PPC_NONE, \
> +                xpnd04_2, PPC_NONE, PPC2_ISA300)
>  
>  GEN_VXFORM_DUAL(vsububm, PPC_ALTIVEC, PPC_NONE, \
>                  bcdadd, PPC_NONE, PPC2_ALTIVEC_207)
> @@ -949,3 +1022,5 @@ GEN_VXFORM_DUAL(vsldoi, PPC_ALTIVEC, PPC_NONE,
>  #undef GEN_VXFORM_NOA
>  #undef GEN_VXFORM_UIMM
>  #undef GEN_VAFORM_PAIRED
> +
> +#undef GEN_BCD2
> diff --git a/target-ppc/translate/vmx-ops.inc.c b/target-ppc/translate/vmx-ops.inc.c
> index 68cba3e..7a5fec6 100644
> --- a/target-ppc/translate/vmx-ops.inc.c
> +++ b/target-ppc/translate/vmx-ops.inc.c
> @@ -122,7 +122,7 @@ GEN_VXFORM_300(vslv, 2, 29),
>  GEN_VXFORM(vslo, 6, 16),
>  GEN_VXFORM(vsro, 6, 17),
>  GEN_VXFORM(vaddcuw, 0, 6),
> -GEN_VXFORM(vsubcuw, 0, 22),
> +GEN_VXFORM_DUAL(vsubcuw, xpnd04_1, 0, 22, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM(vaddubs, 0, 8),
>  GEN_VXFORM(vadduhs, 0, 9),
>  GEN_VXFORM(vadduws, 0, 10),
> @@ -134,7 +134,7 @@ GEN_VXFORM_DUAL(vsubuhs, bcdsub, 0, 25, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM(vsubuws, 0, 26),
>  GEN_VXFORM(vsubsbs, 0, 28),
>  GEN_VXFORM(vsubshs, 0, 29),
> -GEN_VXFORM(vsubsws, 0, 30),
> +GEN_VXFORM_DUAL(vsubsws, xpnd04_2, 0, 30, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM_207(vadduqm, 0, 4),
>  GEN_VXFORM_207(vaddcuq, 0, 5),
>  GEN_VXFORM_DUAL(vaddeuqm, vaddecuq, 30, 0xFF, PPC_NONE, PPC2_ALTIVEC_207),

-- 
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

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