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
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index a156573..356cef8 100644 (file)
--- 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;