Re: [PATCH 3/3] target/openrisc: Setup FPU for detecting tininess before rounding

[Richard Henderson]

On 5/3/23 10:14, Stafford Horne wrote:
> > > +    set_default_nan_mode(1, &cpu->env.fp_status);
> > > +    set_float_detect_tininess(float_tininess_before_rounding,
> > > +                              &cpu->env.fp_status);
> >
> > You don't mention the nan change in the commit message.
>
> Right, and I am not sure I need it.  Let me remove it and run tests again.  I
> was just adding it as a few other architectures did who set
> float_tininess_before_rounding.

What that does is *not* propagate NaN payloads from (some) input to the output.  This is 
certainly true of RISC-V, which specifies this in their architecture manual.  OpenRISC 
does not specify any NaN behaviour at all.

It's not a bad choice, really, and it almost certainly simplifies the design of the FPU, 
as you can do NaN propagation and silencing in one step.


r~