On Tue, Jul 24, 2018 at 12:13:04PM +0000, Yasmin Beatriz wrote:
> After solving a corner case in bcdsub, this patch simplifies the logic
> of both bcdadd/sub instructions by removing some unnecessary local flags.
>
> Signed-off-by: Yasmin Beatriz <yasm...@linux.ibm.com>
> ---
> target/ppc/int_helper.c | 33 +++++++++------------------------
> 1 file changed, 9 insertions(+), 24 deletions(-)
>
> diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c
> index fa18e6e..b8ac4bb 100644
> --- a/target/ppc/int_helper.c
> +++ b/target/ppc/int_helper.c
> @@ -2671,16 +2671,14 @@ static int bcd_cmp_mag(ppc_avr_t *a, ppc_avr_t *b)
> return 0;
> }
>
> -static int bcd_add_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int
> *invalid,
> +static void bcd_add_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int
> *invalid,
> int *overflow)
> {
> int carry = 0;
> int i;
> - int is_zero = 1;
> for (i = 1; i <= 31; i++) {
> uint8_t digit = bcd_get_digit(a, i, invalid) +
> bcd_get_digit(b, i, invalid) + carry;
> - is_zero &= (digit == 0);
> if (digit > 9) {
> carry = 1;
> digit -= 10;
> @@ -2689,26 +2687,20 @@ static int bcd_add_mag(ppc_avr_t *t, ppc_avr_t *a,
> ppc_avr_t *b, int *invalid,
> }
>
> bcd_put_digit(t, digit, i);
> -
> - if (unlikely(*invalid)) {
> - return -1;
> - }
> }
>
> *overflow = carry;
> - return is_zero;
> }
>
> -static int bcd_sub_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int
> *invalid,
> +static void bcd_sub_mag(ppc_avr_t *t, ppc_avr_t *a, ppc_avr_t *b, int
> *invalid,
> int *overflow)
> {
> int carry = 0;
> int i;
> - int is_zero = 1;
> +
> for (i = 1; i <= 31; i++) {
> uint8_t digit = bcd_get_digit(a, i, invalid) -
> bcd_get_digit(b, i, invalid) + carry;
> - is_zero &= (digit == 0);
> if (digit & 0x80) {
> carry = -1;
> digit += 10;
> @@ -2717,14 +2709,9 @@ static int bcd_sub_mag(ppc_avr_t *t, ppc_avr_t *a,
> ppc_avr_t *b, int *invalid,
> }
>
> bcd_put_digit(t, digit, i);
> -
> - if (unlikely(*invalid)) {
> - return -1;
> - }
> }
>
> *overflow = carry;
> - return is_zero;
> }
>
> uint32_t helper_bcdadd(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b, uint32_t
> ps)
> @@ -2734,25 +2721,25 @@ uint32_t helper_bcdadd(ppc_avr_t *r, ppc_avr_t *a,
> ppc_avr_t *b, uint32_t ps)
> int sgnb = bcd_get_sgn(b);
> int invalid = (sgna == 0) || (sgnb == 0);
> int overflow = 0;
> - int zero = 0;
> uint32_t cr = 0;
> ppc_avr_t result = { .u64 = { 0, 0 } };
>
> if (!invalid) {
> if (sgna == sgnb) {
> result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgna, ps);
> - zero = bcd_add_mag(&result, a, b, &invalid, &overflow);
> - cr = (sgna > 0) ? CRF_GT : CRF_LT;
> + bcd_add_mag(&result, a, b, &invalid, &overflow);
> + cr = bcd_cmp_zero(&result);
> } else if (bcd_cmp_mag(a, b) > 0) {
> result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgna, ps);
> - zero = bcd_sub_mag(&result, a, b, &invalid, &overflow);
> + 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);
> + bcd_sub_mag(&result, b, a, &invalid, &overflow);
I don't think you actually need the sub here, since you know the
result is going to be zero.
Although.. in all of the different-sign cases aren't we effectively
doing the subtraction twice - once in bcd_cmp_mag() then again in
bcd_sub_mag()?
> + cr = CRF_EQ;
> } else {
> result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgnb, ps);
> - zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
> + bcd_sub_mag(&result, b, a, &invalid, &overflow);
> cr = (sgnb > 0) ? CRF_GT : CRF_LT;
> }
> }
> @@ -2762,8 +2749,6 @@ uint32_t helper_bcdadd(ppc_avr_t *r, ppc_avr_t *a,
> ppc_avr_t *b, uint32_t ps)
> cr = CRF_SO;
> } else if (overflow) {
> cr |= CRF_SO;
> - } else if (zero) {
> - cr = CRF_EQ;
> }
>
> *r = result;
--
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
signature.asc
Description: PGP signature
