Re: [Qemu-devel] [PATCH 1/2] softfloat: Enable run-time-configurable meaning of signaling NaN bit

[Leon Alrae]

On 25/03/16 12:50, Aleksandar Markovic wrote:
>  
> /*----------------------------------------------------------------------------
>  | The pattern for a default generated single-precision NaN.
>  
> *----------------------------------------------------------------------------*/
> +float32 float32_default_nan(float_status *status) {
>  #if defined(TARGET_SPARC)
> -const float32 float32_default_nan = const_float32(0x7FFFFFFF);
> +    return const_float32(0x7FFFFFFF);
>  #elif defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_ALPHA) || 
> \
>        defined(TARGET_XTENSA) || defined(TARGET_S390X) || 
> defined(TARGET_TRICORE)
> -const float32 float32_default_nan = const_float32(0x7FC00000);
> -#elif SNAN_BIT_IS_ONE
> -const float32 float32_default_nan = const_float32(0x7FBFFFFF);
> +    return const_float32(0x7FC00000);
>  #else
> -const float32 float32_default_nan = const_float32(0xFFC00000);
> +    if (status->snan_bit_is_one)
> +        return const_float32(0x7FBFFFFF);
> +    else
> +        return const_float32(0xFFC00000);

Here for MIPS (when FCR31.NAN2008 is set) we should generate 0x7FC00000
for single-precision. Reference:
"MIPS Architecture For Programmers, Volume I-A: Introduction to the
MIPS64 Architecture", Imagination Technologies LTD., Document Number:
MD00083, Revision 6.01, August 20, 2014, Table 6.3 "Value Supplied When
a New Quiet NaN Is Created", p. 84

Also, for double-precision we should generate 0x7FF8000000000000.

Thanks,
Leon