On Sat, 17 Apr 2021 at 01:02, Richard Henderson
<richard.hender...@linaro.org> wrote:
>
> For Arm BFDOT and BFMMLA, we need a version of round-to-odd
> that overflows to infinity, instead of the max normal number.
>
> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
> ---
> include/fpu/softfloat-types.h | 4 +++-
> fpu/softfloat.c | 8 ++++++--
> 2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/include/fpu/softfloat-types.h b/include/fpu/softfloat-types.h
> index 8a3f20fae9..3b757c3d6a 100644
> --- a/include/fpu/softfloat-types.h
> +++ b/include/fpu/softfloat-types.h
> @@ -134,8 +134,10 @@ typedef enum __attribute__((__packed__)) {
> float_round_up = 2,
> float_round_to_zero = 3,
> float_round_ties_away = 4,
> - /* Not an IEEE rounding mode: round to the closest odd mantissa value */
> + /* Not an IEEE rounding mode: round to closest odd, overflow to max */
> float_round_to_odd = 5,
> + /* Not an IEEE rounding mode: round to closest odd, overflow to inf */
> + float_round_to_odd_inf = 6,
> } FloatRoundMode;
>
> /*
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 67cfa0fd82..76097679b0 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -694,13 +694,12 @@ static FloatParts round_canonical(FloatParts p,
> float_status *s,
>
> switch (p.cls) {
> case float_class_normal:
> + overflow_norm = false;
> switch (s->float_rounding_mode) {
> case float_round_nearest_even:
> - overflow_norm = false;
> inc = ((frac & roundeven_mask) != frac_lsbm1 ? frac_lsbm1 : 0);
> break;
> case float_round_ties_away:
> - overflow_norm = false;
> inc = frac_lsbm1;
> break;
> case float_round_to_zero:
> @@ -717,6 +716,8 @@ static FloatParts round_canonical(FloatParts p,
> float_status *s,
> break;
> case float_round_to_odd:
> overflow_norm = true;
> + /* fall through */
> + case float_round_to_odd_inf:
> inc = frac & frac_lsb ? 0 : round_mask;
> break;
> default:
> @@ -771,6 +772,7 @@ static FloatParts round_canonical(FloatParts p,
> float_status *s,
> ? frac_lsbm1 : 0);
> break;
> case float_round_to_odd:
> + case float_round_to_odd_inf:
> inc = frac & frac_lsb ? 0 : round_mask;
> break;
> default:
> @@ -6860,6 +6862,8 @@ float128 float128_round_to_int(float128 a, float_status
> *status)
>
> case float_round_to_zero:
> break;
> + default:
> + g_assert_not_reached();
> }
> return packFloat128( aSign, 0, 0, 0 );
> }
This code change looks OK as far as it goes, but there are a bunch
of other places in softfloat.c which switch on the float rounding mode.
If this rounding mode is only supported for a particular subset of
operations we should at least document that in the comment.
thanks
-- PMM
