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[Qemu-devel] [PATCH] target/ppc: bcdsub fix sign when result is zero

Yasmin Beatriz posted 1 patch 7 years, 3 months ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/1531767792-17705-1-git-send-email-yasmins@linux.ibm.com
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target/ppc/int_helper.c | 3 +++
1 file changed, 3 insertions(+)
[Qemu-devel] [PATCH] target/ppc: bcdsub fix sign when result is zero
Posted by Yasmin Beatriz 7 years, 3 months ago 
When the result of bcdsub is equal to zero, the result sign may be
set to negative in some cases, and this does not follow the Power ISA
specifications as to decimal integer arithmetic instructions.

Signed-off-by: Yasmin Beatriz <yasmins@linux.ibm.com>
---
 target/ppc/int_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c
index 03d37da..fa18e6e 100644
--- a/target/ppc/int_helper.c
+++ b/target/ppc/int_helper.c
@@ -2747,6 +2747,9 @@ uint32_t helper_bcdadd(ppc_avr_t *r,  ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
             result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgna, ps);
             zero = bcd_sub_mag(&result, a, b, &invalid, &overflow);
             cr = (sgna > 0) ? CRF_GT : CRF_LT;
+        } else if (bcd_cmp_mag(a, b) == 0) {
+            result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(0, ps);
+            zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
         } else {
             result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgnb, ps);
             zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
-- 
1.8.3.1
Re: [Qemu-devel] [PATCH] target/ppc: bcdsub fix sign when result is zero
Posted by David Gibson 7 years, 3 months ago 
On Mon, Jul 16, 2018 at 07:03:12PM +0000, Yasmin Beatriz wrote:
> When the result of bcdsub is equal to zero, the result sign may be
> set to negative in some cases, and this does not follow the Power ISA
> specifications as to decimal integer arithmetic instructions.
> 
> Signed-off-by: Yasmin Beatriz <yasmins@linux.ibm.com>

The fix looks correct, but since this has been broken forever and
we're in hard freeze I'm going to apply for 3.1, not 3.0.

Fwiw, I think the surrounding logic can probably be simplified a
little as well - I think this is now the only case with a zero result,
so I think the 'zero' local can probably be removed.

> ---
>  target/ppc/int_helper.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c
> index 03d37da..fa18e6e 100644
> --- a/target/ppc/int_helper.c
> +++ b/target/ppc/int_helper.c
> @@ -2747,6 +2747,9 @@ uint32_t helper_bcdadd(ppc_avr_t *r,  ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
>              result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgna, ps);
>              zero = bcd_sub_mag(&result, a, b, &invalid, &overflow);
>              cr = (sgna > 0) ? CRF_GT : CRF_LT;
> +        } else if (bcd_cmp_mag(a, b) == 0) {
> +            result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(0, ps);
> +            zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
>          } else {
>              result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgnb, ps);
>              zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);

-- 
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
Re: [Qemu-devel] [PATCH] target/ppc: bcdsub fix sign when result is zero
Posted by Yasmin Beatriz 7 years, 3 months ago 
On Wed, Jul 18, 2018 at 12:22:02PM +1000, David Gibson wrote:
> On Mon, Jul 16, 2018 at 07:03:12PM +0000, Yasmin Beatriz wrote:
> > When the result of bcdsub is equal to zero, the result sign may be
> > set to negative in some cases, and this does not follow the Power ISA
> > specifications as to decimal integer arithmetic instructions.
> > 
> > Signed-off-by: Yasmin Beatriz <yasmins@linux.ibm.com>
> 
> The fix looks correct, but since this has been broken forever and
> we're in hard freeze I'm going to apply for 3.1, not 3.0.
> 
> Fwiw, I think the surrounding logic can probably be simplified a
> little as well - I think this is now the only case with a zero result,
> so I think the 'zero' local can probably be removed.

You are right. I am working on this and will send a new patch very soon.
Thank you for the note.
 
> > ---
> >  target/ppc/int_helper.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c
> > index 03d37da..fa18e6e 100644
> > --- a/target/ppc/int_helper.c
> > +++ b/target/ppc/int_helper.c
> > @@ -2747,6 +2747,9 @@ uint32_t helper_bcdadd(ppc_avr_t *r,  ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
> >              result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgna, ps);
> >              zero = bcd_sub_mag(&result, a, b, &invalid, &overflow);
> >              cr = (sgna > 0) ? CRF_GT : CRF_LT;
> > +        } else if (bcd_cmp_mag(a, b) == 0) {
> > +            result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(0, ps);
> > +            zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
> >          } else {
> >              result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgnb, ps);
> >              zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
> 
> -- 
> 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

Patchew 2.1-devel-b67e4c2

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