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From: frank.chang@sifive.com
To: qemu-devel@nongnu.org, qemu-riscv@nongnu.org
Cc: Frank Chang <frank.chang@sifive.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Subject: [PATCH] target/riscv: fix vssub.vv saturation bug
Date: Mon, 19 Apr 2021 14:01:44 +0800	[thread overview]
Message-ID: <20210419060145.11152-1-frank.chang@sifive.com> (raw)

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



WARNING: multiple messages have this Message-ID (diff)
From: frank.chang@sifive.com
To: qemu-devel@nongnu.org, qemu-riscv@nongnu.org
Cc: Frank Chang <frank.chang@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Subject: [PATCH] target/riscv: fix vssub.vv saturation bug
Date: Mon, 19 Apr 2021 14:01:44 +0800	[thread overview]
Message-ID: <20210419060145.11152-1-frank.chang@sifive.com> (raw)

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



             reply	other threads:[~2021-04-19  6:03 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-19  6:01 frank.chang [this message]
2021-04-19  6:01 ` [PATCH] target/riscv: fix vssub.vv saturation bug frank.chang
2021-04-19  6:25 ` Alistair Francis
2021-04-19  6:25   ` Alistair Francis
2021-04-19  6:31   ` Frank Chang
2021-04-19  6:31     ` Frank Chang
2021-04-19  8:49     ` Alistair Francis
2021-04-19  8:49       ` Alistair Francis

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