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[PATCH] target/riscv: fix vssub.vv saturation bug

frank.chang@sifive.com posted 1 patch 4 years, 7 months ago
Test checkpatch passed
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20210419060145.11152-1-frank.chang@sifive.com
target/riscv/vector_helper.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
[PATCH] target/riscv: fix vssub.vv saturation bug
Posted by frank.chang@sifive.com 4 years, 7 months ago 
From: Frank Chang <frank.chang@sifive.com>

Doing a negate (0x0 – 0x80000000) using vssub.vv produces
an incorrect result of 0x80000000 (should saturate to 0x7fffffff)

Fix this bug by treating zero as a positive number.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
---
 target/riscv/vector_helper.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index a156573d281..356cef8a090 100644
--- a/target/riscv/vector_helper.c
+++ b/target/riscv/vector_helper.c
@@ -2451,7 +2451,7 @@ static inline int8_t ssub8(CPURISCVState *env, int vxrm, int8_t a, int8_t b)
 {
     int8_t res = a - b;
     if ((res ^ a) & (a ^ b) & INT8_MIN) {
-        res = a > 0 ? INT8_MAX : INT8_MIN;
+        res = a >= 0 ? INT8_MAX : INT8_MIN;
         env->vxsat = 0x1;
     }
     return res;
@@ -2461,7 +2461,7 @@ static inline int16_t ssub16(CPURISCVState *env, int vxrm, int16_t a, int16_t b)
 {
     int16_t res = a - b;
     if ((res ^ a) & (a ^ b) & INT16_MIN) {
-        res = a > 0 ? INT16_MAX : INT16_MIN;
+        res = a >= 0 ? INT16_MAX : INT16_MIN;
         env->vxsat = 0x1;
     }
     return res;
@@ -2471,7 +2471,7 @@ static inline int32_t ssub32(CPURISCVState *env, int vxrm, int32_t a, int32_t b)
 {
     int32_t res = a - b;
     if ((res ^ a) & (a ^ b) & INT32_MIN) {
-        res = a > 0 ? INT32_MAX : INT32_MIN;
+        res = a >= 0 ? INT32_MAX : INT32_MIN;
         env->vxsat = 0x1;
     }
     return res;
@@ -2481,7 +2481,7 @@ static inline int64_t ssub64(CPURISCVState *env, int vxrm, int64_t a, int64_t b)
 {
     int64_t res = a - b;
     if ((res ^ a) & (a ^ b) & INT64_MIN) {
-        res = a > 0 ? INT64_MAX : INT64_MIN;
+        res = a >= 0 ? INT64_MAX : INT64_MIN;
         env->vxsat = 0x1;
     }
     return res;
-- 
2.17.1
Re: [PATCH] target/riscv: fix vssub.vv saturation bug
Posted by Alistair Francis 4 years, 7 months ago 
On Mon, Apr 19, 2021 at 4:02 PM <frank.chang@sifive.com> wrote:
>
> From: Frank Chang <frank.chang@sifive.com>
>
> Doing a negate (0x0 – 0x80000000) using vssub.vv produces
> an incorrect result of 0x80000000 (should saturate to 0x7fffffff)
>
> Fix this bug by treating zero as a positive number.
>
> Signed-off-by: Frank Chang <frank.chang@sifive.com>

Thanks for the patch!

A similar fix is already in the riscv-to-apply.next queue

   target/riscv: Fixup saturate subtract function

   The overflow predication ((a - b) ^ a) & (a ^ b) & INT64_MIN is right.
   However, when the predication is ture and a is 0, it should return maximum.

   Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
   Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
   Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
   Message-id: 20210212150256.885-4-zhiwei_liu@c-sky.com
   Message-Id: <20210212150256.885-4-zhiwei_liu@c-sky.com>


Alistair

> ---
>  target/riscv/vector_helper.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> index a156573d281..356cef8a090 100644
> --- a/target/riscv/vector_helper.c
> +++ b/target/riscv/vector_helper.c
> @@ -2451,7 +2451,7 @@ static inline int8_t ssub8(CPURISCVState *env, int vxrm, int8_t a, int8_t b)
>  {
>      int8_t res = a - b;
>      if ((res ^ a) & (a ^ b) & INT8_MIN) {
> -        res = a > 0 ? INT8_MAX : INT8_MIN;
> +        res = a >= 0 ? INT8_MAX : INT8_MIN;
>          env->vxsat = 0x1;
>      }
>      return res;
> @@ -2461,7 +2461,7 @@ static inline int16_t ssub16(CPURISCVState *env, int vxrm, int16_t a, int16_t b)
>  {
>      int16_t res = a - b;
>      if ((res ^ a) & (a ^ b) & INT16_MIN) {
> -        res = a > 0 ? INT16_MAX : INT16_MIN;
> +        res = a >= 0 ? INT16_MAX : INT16_MIN;
>          env->vxsat = 0x1;
>      }
>      return res;
> @@ -2471,7 +2471,7 @@ static inline int32_t ssub32(CPURISCVState *env, int vxrm, int32_t a, int32_t b)
>  {
>      int32_t res = a - b;
>      if ((res ^ a) & (a ^ b) & INT32_MIN) {
> -        res = a > 0 ? INT32_MAX : INT32_MIN;
> +        res = a >= 0 ? INT32_MAX : INT32_MIN;
>          env->vxsat = 0x1;
>      }
>      return res;
> @@ -2481,7 +2481,7 @@ static inline int64_t ssub64(CPURISCVState *env, int vxrm, int64_t a, int64_t b)
>  {
>      int64_t res = a - b;
>      if ((res ^ a) & (a ^ b) & INT64_MIN) {
> -        res = a > 0 ? INT64_MAX : INT64_MIN;
> +        res = a >= 0 ? INT64_MAX : INT64_MIN;
>          env->vxsat = 0x1;
>      }
>      return res;
> --
> 2.17.1
>
>
Re: [PATCH] target/riscv: fix vssub.vv saturation bug
Posted by Frank Chang 4 years, 7 months ago 
Alistair Francis <alistair23@gmail.com> 於 2021年4月19日 週一 下午2:28寫道：

> On Mon, Apr 19, 2021 at 4:02 PM <frank.chang@sifive.com> wrote:
> >
> > From: Frank Chang <frank.chang@sifive.com>
> >
> > Doing a negate (0x0 – 0x80000000) using vssub.vv produces
> > an incorrect result of 0x80000000 (should saturate to 0x7fffffff)
> >
> > Fix this bug by treating zero as a positive number.
> >
> > Signed-off-by: Frank Chang <frank.chang@sifive.com>
>
> Thanks for the patch!
>
> A similar fix is already in the riscv-to-apply.next queue
>
>    target/riscv: Fixup saturate subtract function
>
>    The overflow predication ((a - b) ^ a) & (a ^ b) & INT64_MIN is right.
>    However, when the predication is ture and a is 0, it should return
> maximum.
>
>    Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
>    Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>    Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
>    Message-id: 20210212150256.885-4-zhiwei_liu@c-sky.com
>    Message-Id: <20210212150256.885-4-zhiwei_liu@c-sky.com>
>
>
> Alistair
>

Thanks, I might missed that patch.
Frank Chang


>
> > ---
> >  target/riscv/vector_helper.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> > index a156573d281..356cef8a090 100644
> > --- a/target/riscv/vector_helper.c
> > +++ b/target/riscv/vector_helper.c
> > @@ -2451,7 +2451,7 @@ static inline int8_t ssub8(CPURISCVState *env, int
> vxrm, int8_t a, int8_t b)
> >  {
> >      int8_t res = a - b;
> >      if ((res ^ a) & (a ^ b) & INT8_MIN) {
> > -        res = a > 0 ? INT8_MAX : INT8_MIN;
> > +        res = a >= 0 ? INT8_MAX : INT8_MIN;
> >          env->vxsat = 0x1;
> >      }
> >      return res;
> > @@ -2461,7 +2461,7 @@ static inline int16_t ssub16(CPURISCVState *env,
> int vxrm, int16_t a, int16_t b)
> >  {
> >      int16_t res = a - b;
> >      if ((res ^ a) & (a ^ b) & INT16_MIN) {
> > -        res = a > 0 ? INT16_MAX : INT16_MIN;
> > +        res = a >= 0 ? INT16_MAX : INT16_MIN;
> >          env->vxsat = 0x1;
> >      }
> >      return res;
> > @@ -2471,7 +2471,7 @@ static inline int32_t ssub32(CPURISCVState *env,
> int vxrm, int32_t a, int32_t b)
> >  {
> >      int32_t res = a - b;
> >      if ((res ^ a) & (a ^ b) & INT32_MIN) {
> > -        res = a > 0 ? INT32_MAX : INT32_MIN;
> > +        res = a >= 0 ? INT32_MAX : INT32_MIN;
> >          env->vxsat = 0x1;
> >      }
> >      return res;
> > @@ -2481,7 +2481,7 @@ static inline int64_t ssub64(CPURISCVState *env,
> int vxrm, int64_t a, int64_t b)
> >  {
> >      int64_t res = a - b;
> >      if ((res ^ a) & (a ^ b) & INT64_MIN) {
> > -        res = a > 0 ? INT64_MAX : INT64_MIN;
> > +        res = a >= 0 ? INT64_MAX : INT64_MIN;
> >          env->vxsat = 0x1;
> >      }
> >      return res;
> > --
> > 2.17.1
> >
> >
>
Re: [PATCH] target/riscv: fix vssub.vv saturation bug
Posted by Alistair Francis 4 years, 7 months ago 
On Mon, Apr 19, 2021 at 4:31 PM Frank Chang <0xc0de0125@gmail.com> wrote:
>
> Alistair Francis <alistair23@gmail.com> 於 2021年4月19日 週一 下午2:28寫道：
>>
>> On Mon, Apr 19, 2021 at 4:02 PM <frank.chang@sifive.com> wrote:
>> >
>> > From: Frank Chang <frank.chang@sifive.com>
>> >
>> > Doing a negate (0x0 – 0x80000000) using vssub.vv produces
>> > an incorrect result of 0x80000000 (should saturate to 0x7fffffff)
>> >
>> > Fix this bug by treating zero as a positive number.
>> >
>> > Signed-off-by: Frank Chang <frank.chang@sifive.com>
>>
>> Thanks for the patch!
>>
>> A similar fix is already in the riscv-to-apply.next queue
>>
>>    target/riscv: Fixup saturate subtract function
>>
>>    The overflow predication ((a - b) ^ a) & (a ^ b) & INT64_MIN is right.
>>    However, when the predication is ture and a is 0, it should return maximum.
>>
>>    Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
>>    Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>>    Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
>>    Message-id: 20210212150256.885-4-zhiwei_liu@c-sky.com
>>    Message-Id: <20210212150256.885-4-zhiwei_liu@c-sky.com>
>>
>>
>> Alistair
>
>
> Thanks, I might missed that patch.

No worries. Thanks anyway for the fix.

Alistair

> Frank Chang
>
>>
>>
>> > ---
>> >  target/riscv/vector_helper.c | 8 ++++----
>> >  1 file changed, 4 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
>> > index a156573d281..356cef8a090 100644
>> > --- a/target/riscv/vector_helper.c
>> > +++ b/target/riscv/vector_helper.c
>> > @@ -2451,7 +2451,7 @@ static inline int8_t ssub8(CPURISCVState *env, int vxrm, int8_t a, int8_t b)
>> >  {
>> >      int8_t res = a - b;
>> >      if ((res ^ a) & (a ^ b) & INT8_MIN) {
>> > -        res = a > 0 ? INT8_MAX : INT8_MIN;
>> > +        res = a >= 0 ? INT8_MAX : INT8_MIN;
>> >          env->vxsat = 0x1;
>> >      }
>> >      return res;
>> > @@ -2461,7 +2461,7 @@ static inline int16_t ssub16(CPURISCVState *env, int vxrm, int16_t a, int16_t b)
>> >  {
>> >      int16_t res = a - b;
>> >      if ((res ^ a) & (a ^ b) & INT16_MIN) {
>> > -        res = a > 0 ? INT16_MAX : INT16_MIN;
>> > +        res = a >= 0 ? INT16_MAX : INT16_MIN;
>> >          env->vxsat = 0x1;
>> >      }
>> >      return res;
>> > @@ -2471,7 +2471,7 @@ static inline int32_t ssub32(CPURISCVState *env, int vxrm, int32_t a, int32_t b)
>> >  {
>> >      int32_t res = a - b;
>> >      if ((res ^ a) & (a ^ b) & INT32_MIN) {
>> > -        res = a > 0 ? INT32_MAX : INT32_MIN;
>> > +        res = a >= 0 ? INT32_MAX : INT32_MIN;
>> >          env->vxsat = 0x1;
>> >      }
>> >      return res;
>> > @@ -2481,7 +2481,7 @@ static inline int64_t ssub64(CPURISCVState *env, int vxrm, int64_t a, int64_t b)
>> >  {
>> >      int64_t res = a - b;
>> >      if ((res ^ a) & (a ^ b) & INT64_MIN) {
>> > -        res = a > 0 ? INT64_MAX : INT64_MIN;
>> > +        res = a >= 0 ? INT64_MAX : INT64_MIN;
>> >          env->vxsat = 0x1;
>> >      }
>> >      return res;
>> > --
>> > 2.17.1
>> >
>> >

Patchew 2.1-devel-b67e4c2

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