Re: [Qemu-ppc] [PATCH] 4/4] target-ppc: Implement bcdctz. instruction

[David Gibson]

On Wed, Oct 26, 2016 at 11:18:58AM -0200, Jose Ricardo Ziviani wrote:
> bcdctz. converts from BCD to Zoned numeric format. Zoned format uses
> a byte to represent a digit where the most significant nibble is 0x3
> or 0xf, depending on the preferred signal.
> 
> Signed-off-by: Jose Ricardo Ziviani <address@hidden>
> ---
>  target-ppc/helper.h                 |  1 +
>  target-ppc/int_helper.c             | 54 
> +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  7 +++--
>  3 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index f460635..3b928b8 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -372,6 +372,7 @@ 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_3(bcdcfz, i32, avr, avr, i32)
> +DEF_HELPER_3(bcdctz, 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 8cbbdfc..e0a84bb 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -2768,6 +2768,60 @@ uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, 
> uint32_t ps)
>      *r = ret;
>      return cr;
>  }
> +
> +uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> +{
> +    int i;
> +    int j;
> +    int cr = 0;
> +    int invalid = 0;
> +    uint8_t digit = 0;
> +    int sgnb = bcd_get_sgn(b);
> +    int zone_lead = (ps) ? 0xF0 : 0x30;
> +    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);

This doesn't look right.  The zoned format can accomodate 16 digits.
The low word of the packed format can accomodate 15 digits + sign.  So
it should be possible to convert a packed for with a value in the low
nibble of the upper word.

> +    for (i = 31, j = 16; i > 1; i -= 2, j--) {

Again not seeing any point for the reverse order.

> +        digit = get_nibble(b, j);
> +        ret.u8[BCD_DIG_BYTE(i)] = zone_lead + digit;
> +
> +        if (unlikely(digit > 9)) {
> +            invalid = 1;
> +        }
> +    }
> +
> +    if (unlikely(!sgnb)) {
> +        sgnb = (!get_nibble(b, 0)) ? 1 : -1;
> +    }

Doesn't bcd_get_sgn() returning 0 indicate a badly encoded sign
point.  In which case you should set invalid, rather than making up a
sign according to this apparently arbitrary scheme.

> +
> +    if (ps) {
> +        bcd_put_digit(&ret, (sgnb == 1) ? 0xC : 0xD, 1);
> +    } else {
> +        bcd_put_digit(&ret, (sgnb == 1) ? 0x3 : 0x7, 1);
> +    }
> +    bcd_put_digit(&ret, get_nibble(b, 1), 0);
> +
> +    if (!eq_flag) {
> +        cr = (sgnb == 1) ? 1 << CRF_GT : 1 << CRF_LT;
> +    } 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 9192f8f..62c44f0 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -918,6 +918,7 @@ GEN_BCD(bcdsub)
>  GEN_BCD2(bcdcfn)
>  GEN_BCD3(bcdctn)
>  GEN_BCD2(bcdcfz)
> +GEN_BCD2(bcdctz)
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> @@ -927,7 +928,8 @@ static void gen_xpnd04_1(DisasContext *ctx)
>      case 2:
>          break; /* bcdcfsq. */
>      case 4:
> -        break; /* bcdctz. */
> +        gen_bcdctz(ctx);
> +        break;
>      case 5:
>          gen_bcdctn(ctx);
>          break;
> @@ -952,7 +954,8 @@ static void gen_xpnd04_2(DisasContext *ctx)
>      case 2:
>          break; /* bcdcfsq. */
>      case 4:
> -        break; /* bcdctz. */
> +        gen_bcdctz(ctx);
> +        break;
>      case 6:
>          gen_bcdcfz(ctx);
>          break;

-- 
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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