Re: [Qemu-devel] [PATCH v4 2/6] target-ppc: Implement bcds. instruction

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

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On Mon, Dec 19, 2016 at 02:47:40PM -0200, Jose Ricardo Ziviani wrote:
> bcds.: Decimal shift. Given two registers vra and vrb, this instruction
> shift the vrb value by vra bits into the result register.
> 
> Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> ---
>  target-ppc/helper.h                 |  1 +
>  target-ppc/int_helper.c             | 40 +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  3 +++
>  target-ppc/translate/vmx-ops.inc.c  |  3 ++-
>  4 files changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index 4707db4..1a49b40 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -398,6 +398,7 @@ 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_3(bcdsetsgn, i32, avr, avr, i32)
> +DEF_HELPER_4(bcds, 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 7989b1f..35e14dc 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -3043,6 +3043,46 @@ uint32_t helper_bcdsetsgn(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
>      return bcd_cmp_zero(r);
>  }
>  
> +uint32_t helper_bcds(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
> +{
> +    int cr;
> +#if defined(HOST_WORDS_BIGENDIAN)
> +    int i = a->s8[7];
> +#else
> +    int i = a->s8[8];
> +#endif
> +    bool ox_flag = false;
> +    int sgnb = bcd_get_sgn(b);
> +    ppc_avr_t ret = *b;
> +    ret.u64[LO_IDX] &= ~0xf;
> +
> +    if (bcd_is_valid(b) == false) {
> +        return CRF_SO;
> +    }
> +
> +    if (unlikely(i > 31)) {
> +        i = 31;
> +    } else if (unlikely(i < -31)) {
> +        i = -31;
> +    }
> +
> +    if (i > 0) {
> +        ulshift(&ret.u64[LO_IDX], &ret.u64[HI_IDX], i * 4, &ox_flag);
> +    } else {
> +        urshift(&ret.u64[LO_IDX], &ret.u64[HI_IDX], -i * 4);
> +    }
> +    bcd_put_digit(&ret, bcd_preferred_sgn(sgnb, ps), 0);
> +
> +    *r = ret;
> +
> +    cr = bcd_cmp_zero(r);
> +    if (unlikely(ox_flag)) {

I can imagine use cases where an overflow is not unlikely.  Best to
remove the unlikely() here and let the CPU's dynamic branch prediction
handle it.

> +        cr |= CRF_SO;
> +    }
> +
> +    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 e8e527f..84ebb7e 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -1016,6 +1016,7 @@ GEN_BCD2(bcdcfsq)
>  GEN_BCD2(bcdctsq)
>  GEN_BCD2(bcdsetsgn)
>  GEN_BCD(bcdcpsgn);
> +GEN_BCD(bcds);
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> @@ -1090,6 +1091,8 @@ 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)
> +GEN_VXFORM_DUAL(vsubudm, PPC2_ALTIVEC_207, PPC_NONE, \
> +                bcds, 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 57dce6e..7b4b009 100644
> --- a/target-ppc/translate/vmx-ops.inc.c
> +++ b/target-ppc/translate/vmx-ops.inc.c
> @@ -62,7 +62,8 @@ GEN_VXFORM_207(vaddudm, 0, 3),
>  GEN_VXFORM_DUAL(vsububm, bcdadd, 0, 16, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM_DUAL(vsubuhm, bcdsub, 0, 17, PPC_ALTIVEC, PPC_NONE),
>  GEN_VXFORM(vsubuwm, 0, 18),
> -GEN_VXFORM_207(vsubudm, 0, 19),
> +GEN_VXFORM_DUAL(vsubudm, bcds, 0, 19, PPC2_ALTIVEC_207, PPC2_ISA300),
> +GEN_VXFORM_300(bcds, 0, 27),
>  GEN_VXFORM(vmaxub, 1, 0),
>  GEN_VXFORM(vmaxuh, 1, 1),
>  GEN_VXFORM(vmaxuw, 1, 2),

-- 
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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