[Mesa-stable] [Mesa-dev] [PATCH 24/53] st/nine: Handle RSQ special cases

[Tom Stellard]

On Thu, Jan 08, 2015 at 01:46:32PM +0100, Marek Olšák wrote:
> On Wed, Jan 7, 2015 at 7:09 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> > On Wed, Jan 7, 2015 at 11:36 AM, Axel Davy <axel.davy at ens.fr> wrote:
> >> We should use the absolute value of the input as input to ureg_RSQ.
> >>
> >> Moreover, an input of 0.0 should return FLT_MAX.
> >>
> >> Reviewed-by: David Heidelberg <david at ixit.cz>
> >> Signed-off-by: Axel Davy <axel.davy at ens.fr>
> >>
> >> Cc: "10.4" <mesa-stable at lists.freedesktop.org>
> >> ---
> >>  src/gallium/state_trackers/nine/nine_shader.c | 13 ++++++++++++-
> >>  1 file changed, 12 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/src/gallium/state_trackers/nine/nine_shader.c b/src/gallium/state_trackers/nine/nine_shader.c
> >> index da77da5..4dee5f5 100644
> >> --- a/src/gallium/state_trackers/nine/nine_shader.c
> >> +++ b/src/gallium/state_trackers/nine/nine_shader.c
> >> @@ -1957,6 +1957,17 @@ DECL_SPECIAL(POW)
> >>      return D3D_OK;
> >>  }
> >>
> >> +DECL_SPECIAL(RSQ)
> >> +{
> >> +    struct ureg_program *ureg = tx->ureg;
> >> +    struct ureg_dst dst = tx_dst_param(tx, &tx->insn.dst[0]);
> >> +    struct ureg_src src = tx_src_param(tx, &tx->insn.src[0]);
> >> +    struct ureg_dst tmp = tx_scratch(tx);
> >> +    ureg_RSQ(ureg, tmp, ureg_abs(src));
> >> +    ureg_MIN(ureg, dst, ureg_imm1f(ureg, FLT_MAX), ureg_src(tmp));
> >
> > When would this MIN not return the value in tmp? In the description
> > you say that RSQ(0.0) should return FLT_MAX... is the theory that
> > MIN(NaN, FLT_MAX) == FLT_MAX? Is RSQ(0) in tgsi defined to return NaN?
> 
> No, because legacy versions of MIN and MAX aren't commutative. To
> clarify this more, the legacy versions of MIN/MAX return x if either
> operand is NaN (non-commutative), while DX10 versions return the one
> that isn't NaN (commutative). For compatibility with the legacy
> versions, the FLT_MAX constant must be in x.
> 

Is it documented anywhere how min/max and other tgsi comparison instructions
are supposed to handle NaN and +-inf?  If not, we really need to get this
documented somewhere.

-Tom

> Marek
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