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

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

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On Wed, Nov 16, 2016 at 06:07:29PM -0200, Jose Ricardo Ziviani wrote:
> bcdcpsgn.: Decimal copy sign. Given two registers vra and vrb, it
> copies the vra value with vrb sign to the result register vrt.
> 
> Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> ---
>  target-ppc/helper.h                 |  1 +
>  target-ppc/int_helper.c             | 30 ++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  3 +++
>  target-ppc/translate/vmx-ops.inc.c  |  2 +-
>  4 files changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index 503f257..dada48e 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -384,6 +384,7 @@ DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
>  DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
>  DEF_HELPER_3(bcdcfsq, i32, avr, avr, i32)
>  DEF_HELPER_3(bcdctsq, i32, avr, avr, i32)
> +DEF_HELPER_4(bcdcpsgn, i32, avr, 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 1025438..a215bfe 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -2961,6 +2961,36 @@ uint32_t helper_bcdctsq(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
>      return cr;
>  }
>  
> +uint32_t helper_bcdcpsgn(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
> +{
> +    int i;
> +    int cr = 0;
> +    int sgna = bcd_get_sgn(a);
> +    int sgnb = bcd_get_sgn(b);
> +    int invalid = (sgna == 0) || (sgnb == 0);
> +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> +
> +    for (i = 1; i < 32; i++) {
> +        bcd_put_digit(&ret, bcd_get_digit(a, i, &invalid), i);
> +        bcd_get_digit(b, i, &invalid);

This is a lot of bit fiddling to accomplish what you could pretty much
do just by copying the entire register.  Checking for invalid input
makes it a bit more complex than that, of course, but you still don't
need to assemble every digit separately in the target.

> +
> +        if (unlikely(invalid)) {
> +            break;
> +        }
> +    }
> +    bcd_put_digit(&ret, bcd_get_digit(b, 0, &invalid), 0);

This won't work.  bcd_get_digit() will set invalid if digit 0 is an
invalid *digit*.  But some valid sign indicators are not valid digits,
so this will erroneously set invalid in those cases.

> +
> +    cr = bcd_cmp_zero(a);
> +
> +    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 1579b58..c14b666 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -991,6 +991,7 @@ GEN_BCD2(bcdcfz)
>  GEN_BCD2(bcdctz)
>  GEN_BCD2(bcdcfsq)
>  GEN_BCD2(bcdctsq)
> +GEN_BCD(bcdcpsgn);
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> @@ -1056,6 +1057,8 @@ GEN_VXFORM_DUAL(vsubuhm, PPC_ALTIVEC, PPC_NONE, \
>                  bcdsub, PPC_NONE, PPC2_ALTIVEC_207)
>  GEN_VXFORM_DUAL(vsubuhs, PPC_ALTIVEC, PPC_NONE, \
>                  bcdsub, PPC_NONE, PPC2_ALTIVEC_207)
> +GEN_VXFORM_DUAL(vaddshs, PPC_ALTIVEC, PPC_NONE, \
> +                bcdcpsgn, PPC_NONE, PPC2_ISA300)
>  
>  static void gen_vsbox(DisasContext *ctx)
>  {
> diff --git a/target-ppc/translate/vmx-ops.inc.c b/target-ppc/translate/vmx-ops.inc.c
> index f02b3be..70d7d2b 100644
> --- a/target-ppc/translate/vmx-ops.inc.c
> +++ b/target-ppc/translate/vmx-ops.inc.c
> @@ -131,7 +131,7 @@ GEN_VXFORM_DUAL(vaddubs, vmul10uq, 0, 8, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM_DUAL(vadduhs, vmul10euq, 0, 9, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM(vadduws, 0, 10),
>  GEN_VXFORM(vaddsbs, 0, 12),
> -GEN_VXFORM(vaddshs, 0, 13),
> +GEN_VXFORM_DUAL(vaddshs, bcdcpsgn, 0, 13, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM(vaddsws, 0, 14),
>  GEN_VXFORM_DUAL(vsububs, bcdadd, 0, 24, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM_DUAL(vsubuhs, bcdsub, 0, 25, PPC_ALTIVEC, PPC_NONE),

-- 
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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