Re: [Qemu-ppc] [PATCH] 3/4] target-ppc: Implement bcdcfz. instruction

[David Gibson]

On Wed, Oct 26, 2016 at 11:18:57AM -0200, Jose Ricardo Ziviani wrote:
> bcdcfz. converts from Zoned numeric format to BCD. 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             | 55 
> +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  7 +++--
>  3 files changed, 61 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index 92eaaf0..f460635 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -371,6 +371,7 @@ 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_3(bcdcfz, 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 cffe82c..8cbbdfc 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -2459,6 +2459,17 @@ static int bcd_preferred_sgn(int sgn, int ps)
>      }
>  }
>  
> +static uint8_t get_nibble(ppc_avr_t *bcd, int n)
> +{
> +    uint8_t result;
> +    if (!(n & 1)) {
> +        result = bcd->u8[BCD_DIG_BYTE(n)] & 0xF;
> +    } else {
> +       result = bcd->u8[BCD_DIG_BYTE(n)] >> 4;
> +    }
> +    return result;
> +}

This can be merged with bcd_get_digit() without too much effort.

>  static uint8_t bcd_get_digit(ppc_avr_t *bcd, int n, int *invalid)
>  {
>      uint8_t result;
> @@ -2713,6 +2724,50 @@ uint32_t helper_bcdctn(ppc_avr_t *r, ppc_avr_t *b)
>      return cr;
>  }
>  
> +uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> +{
> +    int i;
> +    int j = 0;
> +    int cr = 0;
> +    int invalid = 0;
> +    int eq_flag = 0;
> +    int zone_digit = 0;
> +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> +    int sgnb = get_nibble(b, 1);
> +
> +    if (unlikely(((sgnb < 0xA) && ps) ||
> +                ((get_nibble(b, 0) > 0x9) && !ps))) {

The second half of this condition doesn't belong here.  It's a
requirement for both ps values, and would make more sense applied
along with the same test on the other digits.

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

I don't see why you're doing this in reverse order.

> +        zone_digit = get_nibble(b, i);
> +        if (unlikely((ps && zone_digit != 0xF) ||
> +                    (!ps && zone_digit != 0x3))) {
> +            invalid = 1;

In this and the other instructions it would make sense to break out of
the function as soon as you detect an invalid encoding.

> +        }

You never check for invalid encoding in the low input nibble
(i.e. value > 0x9).

> +        eq_flag += zone_digit;

What?? How on earth does adding up the zone digits help you.  For a
valid encoding the answer should always be either 0x2d (PS=0) or 0xe1
(PS=1).

> +        bcd_put_digit(&ret, get_nibble(b, i - 1), j);
> +    }
> +    bcd_put_digit(&ret, get_nibble(b, 0), 1);
> +
> +    if ((ps && (sgnb == 0xB || sgnb == 0xD)) ||
> +            (!ps && (sgnb & 0x4))) {
> +        bcd_put_digit(&ret, BCD_NEG_PREF, 0);
> +        cr = (!eq_flag) ? 1 << CRF_LT : 1 << CRF_EQ;
> +    } else {
> +        bcd_put_digit(&ret, BCD_PLUS_PREF_1, 0);
> +        cr = (!eq_flag) ? 1 << CRF_GT : 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 4364881..9192f8f 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -917,6 +917,7 @@ GEN_BCD(bcdadd)
>  GEN_BCD(bcdsub)
>  GEN_BCD2(bcdcfn)
>  GEN_BCD3(bcdctn)
> +GEN_BCD2(bcdcfz)
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> @@ -931,7 +932,8 @@ static void gen_xpnd04_1(DisasContext *ctx)
>          gen_bcdctn(ctx);
>          break;
>      case 6:
> -        break; /* bcdcfz. */
> +        gen_bcdcfz(ctx);
> +        break;
>      case 7:
>          gen_bcdcfn(ctx);
>          break;
> @@ -952,7 +954,8 @@ static void gen_xpnd04_2(DisasContext *ctx)
>      case 4:
>          break; /* bcdctz. */
>      case 6:
> -        break; /* bcdcfz. */
> +        gen_bcdcfz(ctx);
> +        break;
>      case 7:
>          gen_bcdcfn(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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