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Re: [Qemu-arm] [PATCH] softfloat: Handle default NaN mode after pickNaNM
From: |
Alex Bennée |
Subject: |
Re: [Qemu-arm] [PATCH] softfloat: Handle default NaN mode after pickNaNMulAdd, not before |
Date: |
Tue, 08 May 2018 12:30:28 +0100 |
User-agent: |
mu4e 1.1.0; emacs 26.1 |
Peter Maydell <address@hidden> writes:
> It is implementation defined whether a multiply-add of
> (0,inf,qnan) or (inf,0,qnan) raises InvalidaOperation or
> not, so we let the target-specific pickNaNMulAdd function
> handle this. This means that we must do the "return the
> default NaN in default NaN mode" check after the call,
> not before. Correct the ordering, and restore the comment
> from the old propagateFloat64MulAddNaN() that warned about
> this corner case.
>
> This fixes a regression from 2.11 for Arm guests where we would
> incorrectly fail to set the Invalid flag for these cases.
>
> Cc: address@hidden
> Signed-off-by: Peter Maydell <address@hidden>
Reviewed-by: Alex Bennée <address@hidden>
Tested-by: Alex Bennée <address@hidden>
> ---
> fpu/softfloat.c | 52 ++++++++++++++++++++++++++++---------------------
> 1 file changed, 30 insertions(+), 22 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 70e0c40a1c..8401b37bd4 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -602,34 +602,42 @@ static FloatParts pick_nan(FloatParts a, FloatParts b,
> float_status *s)
> static FloatParts pick_nan_muladd(FloatParts a, FloatParts b, FloatParts c,
> bool inf_zero, float_status *s)
> {
> + int which;
> +
> if (is_snan(a.cls) || is_snan(b.cls) || is_snan(c.cls)) {
> s->float_exception_flags |= float_flag_invalid;
> }
>
> - if (s->default_nan_mode) {
> - a.cls = float_class_dnan;
> - } else {
> - switch (pickNaNMulAdd(is_qnan(a.cls), is_snan(a.cls),
> - is_qnan(b.cls), is_snan(b.cls),
> - is_qnan(c.cls), is_snan(c.cls),
> - inf_zero, s)) {
> - case 0:
> - break;
> - case 1:
> - a = b;
> - break;
> - case 2:
> - a = c;
> - break;
> - case 3:
> - a.cls = float_class_dnan;
> - return a;
> - default:
> - g_assert_not_reached();
> - }
> + which = pickNaNMulAdd(is_qnan(a.cls), is_snan(a.cls),
> + is_qnan(b.cls), is_snan(b.cls),
> + is_qnan(c.cls), is_snan(c.cls),
> + inf_zero, s);
>
> - a.cls = float_class_msnan;
> + if (s->default_nan_mode) {
> + /* Note that this check is after pickNaNMulAdd so that function
> + * has an opportunity to set the Invalid flag.
> + */
> + a.cls = float_class_dnan;
> + return a;
> }
> +
> + switch (which) {
> + case 0:
> + break;
> + case 1:
> + a = b;
> + break;
> + case 2:
> + a = c;
> + break;
> + case 3:
> + a.cls = float_class_dnan;
> + return a;
> + default:
> + g_assert_not_reached();
> + }
> + a.cls = float_class_msnan;
> +
> return a;
> }
--
Alex Bennée