Re: [Qemu-devel] [PATCH] Fix NaN handling in softfloat

[Aurelien Jarno <aurelien@aurel32.net>]

Aurelien Jarno a écrit :
>> I have looked quickly at your patch, it looks like the right approach to
>> define target specific things at only one place in the file. I will get
>> a closer tomorrow.
>>
> 
> Sorry I have been busy with real life stuff, and haven't looked at your
> patch. I have seen you have committed it.
> 
> I have rebased the patch I already posted against the current CVS, it is
> less intrusive now. It defines float32_default_nan and 
> float64_default_nan for the various targets, as it varies even within 
> targets which have the same convention for the SNAN bit.
> 
> It also keeps the mantissa when converting FP numbers, so that qNaN are
> not changed into sNaN on MIPS and HPPA. If the mantissa becames zero a
> new NaN number is generated.
> 
> It finally fixes an off-by-one in the extended double precision
> format (aka floatx80), the mantissa is 64-bit long and not 63-bit
> long.
> 
> With this patch applied all the glibc 2.7 floating point tests
> are successfull on MIPS and MIPSEL.


Any news about this patch?



> Index: fpu/softfloat-specialize.h
> ===================================================================
> RCS file: /sources/qemu/qemu/fpu/softfloat-specialize.h,v
> retrieving revision 1.5
> diff -u -d -p -r1.5 softfloat-specialize.h
> --- fpu/softfloat-specialize.h	18 Nov 2007 14:33:23 -0000	1.5
> +++ fpu/softfloat-specialize.h	20 Nov 2007 23:18:44 -0000
> @@ -65,7 +65,13 @@ typedef struct {
>  /*----------------------------------------------------------------------------
>  | The pattern for a default generated single-precision NaN.
>  *----------------------------------------------------------------------------*/
> -#if SNAN_BIT_IS_ONE
> +#if defined(TARGET_SPARC)
> +#define float32_default_nan make_float32(0x7FFFFFFF)
> +#elif defined(TARGET_POWERPC)
> +#define float32_default_nan make_float32(0x7FC00000)
> +#elif defined(TARGET_HPPA)
> +#define float32_default_nan make_float32(0x7FA00000)
> +#elif SNAN_BIT_IS_ONE
>  #define float32_default_nan make_float32(0x7FBFFFFF)
>  #else
>  #define float32_default_nan make_float32(0xFFC00000)
> @@ -125,8 +131,12 @@ static commonNaNT float32ToCommonNaN( fl
>  
>  static float32 commonNaNToFloat32( commonNaNT a )
>  {
> -    return make_float32(
> -        ( ( (bits32) a.sign )<<31 ) | 0x7FC00000 | ( a.high>>41 ) );
> +    bits32 mantissa = a.high>>41;
> +    if ( mantissa )
> +        return make_float32(
> +            ( ( (bits32) a.sign )<<31 ) | 0x7F800000 | ( a.high>>41 ) );
> +    else
> +        return float32_default_nan;
>  }
>  
>  /*----------------------------------------------------------------------------
> @@ -180,7 +190,13 @@ static float32 propagateFloat32NaN( floa
>  /*----------------------------------------------------------------------------
>  | The pattern for a default generated double-precision NaN.
>  *----------------------------------------------------------------------------*/
> -#if SNAN_BIT_IS_ONE
> +#if defined(TARGET_SPARC)
> +#define float64_default_nan make_float64(LIT64( 0x7FFFFFFFFFFFFFFF ))
> +#elif defined(TARGET_POWERPC)
> +#define float64_default_nan make_float64(LIT64( 0x7FF8000000000000 ))
> +#elif defined(TARGET_HPPA)
> +#define float64_default_nan make_float64(LIT64( 0x7FF4000000000000 ))
> +#elif SNAN_BIT_IS_ONE
>  #define float64_default_nan make_float64(LIT64( 0x7FF7FFFFFFFFFFFF ))
>  #else
>  #define float64_default_nan make_float64(LIT64( 0xFFF8000000000000 ))
> @@ -244,10 +260,15 @@ static commonNaNT float64ToCommonNaN( fl
>  
>  static float64 commonNaNToFloat64( commonNaNT a )
>  {
> -    return make_float64(
> -          ( ( (bits64) a.sign )<<63 )
> -        | LIT64( 0x7FF8000000000000 )
> -        | ( a.high>>12 ));
> +    bits64 mantissa = a.high>>12;
> +
> +    if ( mantissa )
> +        return make_float64(
> +              ( ( (bits64) a.sign )<<63 )
> +            | LIT64( 0x7FF0000000000000 )
> +            | ( a.high>>12 ));
> +    else
> +        return float64_default_nan;
>  }
>  
>  /*----------------------------------------------------------------------------
> @@ -366,7 +387,7 @@ static commonNaNT floatx80ToCommonNaN( f
>      if ( floatx80_is_signaling_nan( a ) ) float_raise( float_flag_invalid STATUS_VAR);
>      z.sign = a.high>>15;
>      z.low = 0;
> -    z.high = a.low<<1;
> +    z.high = a.low;
>      return z;
>  }
>  
> @@ -379,7 +400,10 @@ static floatx80 commonNaNToFloatx80( com
>  {
>      floatx80 z;
>  
> -    z.low = LIT64( 0xC000000000000000 ) | ( a.high>>1 );
> +    if (a.high)
> +        z.low = a.high;
> +    else
> +        z.low = floatx80_default_nan_low;
>      z.high = ( ( (bits16) a.sign )<<15 ) | 0x7FFF;
>      return z;
>  }
> @@ -500,7 +524,7 @@ static float128 commonNaNToFloat128( com
>      float128 z;
>  
>      shift128Right( a.high, a.low, 16, &z.high, &z.low );
> -    z.high |= ( ( (bits64) a.sign )<<63 ) | LIT64( 0x7FFF800000000000 );
> +    z.high |= ( ( (bits64) a.sign )<<63 ) | LIT64( 0x7FFF000000000000 );
>      return z;
>  }
>  
> 


-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32@debian.org         | aurelien@aurel32.net
   `-    people.debian.org/~aurel32 | www.aurel32.net