Re: [Qemu-devel] [PATCH v3 3/4] target-ppc: Implement bcdcfz. instruction

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

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On Mon, Oct 31, 2016 at 03:34:48PM -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 <joserz@linux.vnet.ibm.com>
> ---
>  target-ppc/helper.h                 |  1 +
>  target-ppc/int_helper.c             | 48 +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  7 ++++--
>  3 files changed, 54 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index 33286c6..8546bb9 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -373,6 +373,7 @@ 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_3(bcdctn, i32, avr, avr, i32)
> +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 aaaf642..6581887 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -2727,6 +2727,54 @@ uint32_t helper_bcdctn(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
>      return cr;
>  }
>  
> +uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> +{
> +    int i;
> +    int j;
> +    int cr = 0;
> +    int invalid = 0;
> +    int neq_flag = 0;
> +    int zone_digit = 0;
> +    int zone_lead = ps ? 0xF : 0x3;
> +    int digit = 0;
> +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> +    int sgnb = b->u8[BCD_DIG_BYTE(0)] >> 4;
> +
> +    if (unlikely((sgnb < 0xA) && ps)) {
> +        invalid = 1;
> +    }
> +
> +    for (i = 0, j = 1; i < 31; i += 2, j++) {
> +        zone_digit = (i) ? b->u8[BCD_DIG_BYTE(i)] >> 4 : zone_lead;
> +        digit = b->u8[BCD_DIG_BYTE(i)] & 0xF;
> +
> +        if (unlikely(zone_digit != zone_lead || digit > 0x9)) {
> +            invalid = 1;
> +            break;
> +        }
> +
> +        neq_flag += (digit != 0);
> +        bcd_put_digit(&ret, digit, j);
> +    }
> +
> +    if ((ps && (sgnb == 0xB || sgnb == 0xD)) ||
> +            (!ps && (sgnb & 0x4))) {
> +        bcd_put_digit(&ret, BCD_NEG_PREF, 0);
> +        cr = (neq_flag) ? 1 << CRF_LT : 1 << CRF_EQ;
> +    } else {
> +        bcd_put_digit(&ret, BCD_PLUS_PREF_1, 0);
> +        cr = (neq_flag) ? 1 << CRF_GT : 1 << CRF_EQ;
> +    }

As with bcdcfn., you can test for zero on the final result more easily
than building up the neq_flag as you go.

Actually.. rather than having a bcd_is_zero() as I suggested on the
other patch, you could have a helper that returns all the EQ, LT, GT
flags for a given BCD input.  You should be able to use that in all
these instructions (except for the invalid case, obviously) - on the
output value for bcdcfn. and bcdcfz. and on the input value for
bcdctn. and bcdctz.

> +
> +    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 301088e..ecf0e54 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -972,6 +972,7 @@ GEN_BCD(bcdadd)
>  GEN_BCD(bcdsub)
>  GEN_BCD2(bcdcfn)
>  GEN_BCD2(bcdctn)
> +GEN_BCD2(bcdcfz)
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> @@ -986,7 +987,8 @@ 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;
> @@ -1008,7 +1010,8 @@ 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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