Re: [Qemu-devel] [PATCH v3] Softfloat: Add support to softfloat to return floatxx_default_nan when, the corresponding target status flag is set.

[Peter Maydell <peter.maydell@linaro.org>]

On 7 February 2011 17:00, Christophe Lyon <christophe.lyon@st.com> wrote:
>
> Some CPUs have a status flag imposing to return floatxx_default_nan
> whatever the input value, when converting from one FP format to
> another. Implement this, using the already existing default_nan_mode
> status flag (currently used on ARM and SH4 at the moment).
>
> Signed-off-by: Christophe Lyon <christophe.lyon@st.com>

Your subject is a bit long, which can make it wrap annoyingly in git logs.
I'd suggest something like:

===begin===
softfloat: Honour default_nan_mode for float-to-float conversions

Honour the default_nan_mode flag when doing conversions between
different floating point formats, as well as when returning a NaN from
a two-operand floating point function. This corrects the behaviour
of float<->double conversions on both ARM and SH4.
===endit===

> +/*----------------------------------------------------------------------------
> +| The pattern for a default generated haft-precision NaN.
> +*----------------------------------------------------------------------------*/

"half-precision".

> @@ -2767,11 +2767,7 @@ bits16 float32_to_float16( float32 a, flag ieee STATUS_PARAM)
>     aExp = extractFloat32Exp( a );
>     aSign = extractFloat32Sign( a );
>     if ( aExp == 0xFF ) {
> -        if (aSig) {
> -            /* Make sure correct exceptions are raised.  */
> -            float32ToCommonNaN(a STATUS_VAR);
> -            aSig |= 0x00400000;
> -        }
> +        if ( aSig ) return commonNaNToFloat16( float32ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
>         return packFloat16(aSign, 0x1f, aSig >> 13);
>     }
>     if (aExp == 0 && aSign == 0) {

This is float32_to_float16() but it looks like you've missed
float16_to_float32() ?

Otherwise, looks good, and I can confirm that it fixes
behaviour of VCVT.F32.F64 and VCVT.F64.F32 when
the FPSCR.DN bit is set.

-- PMM