Re: [Qemu-devel] [PATCH 5/7] target-ppc: Implement bcdsr. instruction

[David Gibson]

On Sat, Dec 03, 2016 at 03:00:04AM -0200, Jose Ricardo Ziviani wrote:
> bcdsr.: Decimal shift and round. This instruction works like bcds.
> however, when performing right shift, 1 will be added to the
> result if the last digit was >= 5.
> 
> Signed-off-by: Jose Ricardo Ziviani <address@hidden>
> ---
>  target-ppc/helper.h                 |  1 +
>  target-ppc/int_helper.c             | 45 
> +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  1 +
>  target-ppc/translate/vmx-ops.inc.c  |  2 ++
>  4 files changed, 49 insertions(+)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index 386ea67..d9528eb 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -394,6 +394,7 @@ 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_4(bcdus, i32, avr, avr, avr, i32)
> +DEF_HELPER_4(bcdsr, 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 4b5eea1..c9fcb1a 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -3124,6 +3124,51 @@ uint32_t helper_bcdus(ppc_avr_t *r, ppc_avr_t *a, 
> ppc_avr_t *b, uint32_t ps)
>      return cr;
>  }
>  
> +uint32_t helper_bcdsr(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
> +{
> +    int cr;
> +    int i;
> +    int unused = 0;
> +    int invalid = 0;
> +    bool ox_flag = false;
> +    int sgnb = bcd_get_sgn(b);
> +    ppc_avr_t ret = *b;
> +    ret.u64[LO_IDX] &= ~0xf;
> +
> +#if defined(HOST_WORDS_BIGENDIAN)
> +    ppc_avr_t bcd_one = { .u64 = { 0, 0x10 } };
> +    int upper = ARRAY_SIZE(a->s32) - 1;

Same comment as previous patches about the shift argument.

> +#else
> +    ppc_avr_t bcd_one = { .u64 = { 0x10, 0 } };
> +    int upper = 0;
> +#endif
> +
> +    if (bcd_is_valid(b) == false) {
> +        return CRF_SO;
> +    }
> +
> +    if (a->s32[upper] > 0) {
> +        i = (a->s32[upper] > 31) ? 31 : a->s32[upper];
> +        ulshift(&ret.u64[LO_IDX], &ret.u64[HI_IDX], i * 4, &ox_flag);
> +    } else {
> +        i = (a->s32[upper] < -31) ? 31 : -a->s32[upper];
> +        urshift(&ret.u64[LO_IDX], &ret.u64[HI_IDX], i * 4);
> +
> +        if (bcd_get_digit(&ret, 0, &invalid) >= 5) {

So, the ISA actually says you increment only if the last digit is >
5.  That doesn't seem like correct rounding, so it might be an error
in the ISA document - best check this with the hardware people.

> +            bcd_add_mag(&ret, &ret, &bcd_one, &invalid, &unused);
> +        }
> +    }
> +    bcd_put_digit(&ret, bcd_preferred_sgn(sgnb, ps), 0);
> +
> +    cr = bcd_cmp_zero(&ret);
> +    if (unlikely(ox_flag)) {
> +        cr |= 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 fc54881..451abb5 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -1018,6 +1018,7 @@ GEN_BCD2(bcdsetsgn)
>  GEN_BCD(bcdcpsgn);
>  GEN_BCD(bcds);
>  GEN_BCD(bcdus);
> +GEN_BCD(bcdsr);
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> diff --git a/target-ppc/translate/vmx-ops.inc.c 
> b/target-ppc/translate/vmx-ops.inc.c
> index cdd3abe..fa9c996 100644
> --- a/target-ppc/translate/vmx-ops.inc.c
> +++ b/target-ppc/translate/vmx-ops.inc.c
> @@ -132,6 +132,8 @@ GEN_HANDLER_E_2(vprtybd, 0x4, 0x1, 0x18, 9, 0, PPC_NONE, 
> PPC2_ISA300),
>  GEN_HANDLER_E_2(vprtybq, 0x4, 0x1, 0x18, 10, 0, PPC_NONE, PPC2_ISA300),
>  
>  GEN_VXFORM_DUAL(vsubcuw, xpnd04_1, 0, 22, PPC_ALTIVEC, PPC_NONE),
> +GEN_VXFORM_300(bcdsr, 0, 23),
> +GEN_VXFORM_300(bcdsr, 0, 31),
>  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),

-- 
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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