Re: [Qemu-devel] [PATCH] target-arm: Squash input denormals in FRECPS and FRSQRTS

[Greg Bellows <greg.bellows@linaro.org>]

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On Fri, Jan 30, 2015 at 3:41 AM, Laurent Desnogues <
laurent.desnogues@gmail.com> wrote:

> On Thu, Jan 29, 2015 at 8:31 PM, Peter Maydell <peter.maydell@linaro.org>
> wrote:
> > The helper functions for FRECPS and FRSQRTS have special case
> > handling that includes checks for zero inputs, so squash input
> > denormals if necessary before those checks. This fixes incorrect
> > output when the FPCR DZ bit is set to enable squashing of input
> > denormals.
> >
> > Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>
> Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
>
> Thanks,
>
> Laurent
>
> > ---
> > A quick eyeball of helper-a64.c suggests that these are the only
> > other insns we needed to fix, and a risu test of these insns
> > confirms that (a) they're buggy and (b) this patch fixes them.
> > I haven't done an exhaustive coverage test of the whole instruction
> > set with the DZ bit set, though...
> >
> >  target-arm/helper-a64.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/target-arm/helper-a64.c b/target-arm/helper-a64.c
> > index ebd9247..8aa40e9 100644
> > --- a/target-arm/helper-a64.c
> > +++ b/target-arm/helper-a64.c
> > @@ -229,6 +229,9 @@ float32 HELPER(recpsf_f32)(float32 a, float32 b,
> void *fpstp)
> >  {
> >      float_status *fpst = fpstp;
> >
> > +    a = float32_squash_input_denormal(a, fpst);
> > +    b = float32_squash_input_denormal(b, fpst);
> > +
> >      a = float32_chs(a);
> >      if ((float32_is_infinity(a) && float32_is_zero(b)) ||
> >          (float32_is_infinity(b) && float32_is_zero(a))) {
> > @@ -241,6 +244,9 @@ float64 HELPER(recpsf_f64)(float64 a, float64 b,
> void *fpstp)
> >  {
> >      float_status *fpst = fpstp;
> >
> > +    a = float64_squash_input_denormal(a, fpst);
> > +    b = float64_squash_input_denormal(b, fpst);
> > +
> >      a = float64_chs(a);
> >      if ((float64_is_infinity(a) && float64_is_zero(b)) ||
> >          (float64_is_infinity(b) && float64_is_zero(a))) {
> > @@ -253,6 +259,9 @@ float32 HELPER(rsqrtsf_f32)(float32 a, float32 b,
> void *fpstp)
> >  {
> >      float_status *fpst = fpstp;
> >
> > +    a = float32_squash_input_denormal(a, fpst);
> > +    b = float32_squash_input_denormal(b, fpst);
> > +
> >      a = float32_chs(a);
> >      if ((float32_is_infinity(a) && float32_is_zero(b)) ||
> >          (float32_is_infinity(b) && float32_is_zero(a))) {
> > @@ -265,6 +274,9 @@ float64 HELPER(rsqrtsf_f64)(float64 a, float64 b,
> void *fpstp)
> >  {
> >      float_status *fpst = fpstp;
> >
> > +    a = float64_squash_input_denormal(a, fpst);
> > +    b = float64_squash_input_denormal(b, fpst);
> > +
> >      a = float64_chs(a);
> >      if ((float64_is_infinity(a) && float64_is_zero(b)) ||
> >          (float64_is_infinity(b) && float64_is_zero(a))) {
> > --
> > 1.9.1
> >
> >
>
>
​Reviewed-by: Greg Bellows <greg.bellows@linaro.org>​

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