On Mon, Apr 19, 2021 at 4:02 PM <frank.ch...@sifive.com> wrote:
>
> From: Frank Chang <frank.ch...@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.ch...@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_...@c-sky.com>
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
Reviewed-by: Alistair Francis <alistair.fran...@wdc.com>
Message-id: 20210212150256.885-4-zhiwei_...@c-sky.com
Message-Id: <20210212150256.885-4-zhiwei_...@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
>
>
