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

[Thiemo Seufer]

Aurelien Jarno wrote:
> Hi all,
> 
> The current softfloat implementation changes qNaN into sNaN when 
> converting between formats, for no reason. The attached patch fixes
> that.

Did you take into account that MIPS and PA-RISC have the signalling
bit inverted to the rest of the world?

> It also 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.
> 
> Bye,
> Aurelien
> 
> Index: fpu/softfloat-specialize.h
> ===================================================================
> RCS file: /sources/qemu/qemu/fpu/softfloat-specialize.h,v
> retrieving revision 1.3
> diff -u -d -p -r1.3 softfloat-specialize.h
> --- fpu/softfloat-specialize.h        11 May 2007 17:10:14 -0000      1.3
> +++ fpu/softfloat-specialize.h        3 Nov 2007 17:21:38 -0000
> @@ -121,8 +121,7 @@ static commonNaNT float32ToCommonNaN( fl
>  static float32 commonNaNToFloat32( commonNaNT a )
>  {
>  
> -    return ( ( (bits32) a.sign )<<31 ) | 0x7FC00000 | ( a.high>>41 );
> -
> +    return ( ( (bits32) a.sign )<<31 ) | 0x7F800000 | ( a.high>>41 );
>  }
>  
>  
> /*----------------------------------------------------------------------------
> @@ -233,7 +232,7 @@ static float64 commonNaNToFloat64( commo
>  
>      return
>            ( ( (bits64) a.sign )<<63 )
> -        | LIT64( 0x7FF8000000000000 )
> +        | LIT64( 0x7FF0000000000000 )
>          | ( a.high>>12 );
>  
>  }
> @@ -329,7 +328,7 @@ 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;
>  
>  }
> @@ -343,7 +342,7 @@ static floatx80 commonNaNToFloatx80( com
>  {
>      floatx80 z;
>  
> -    z.low = LIT64( 0xC000000000000000 ) | ( a.high>>1 );
> +    z.low = a.high;
>      z.high = ( ( (bits16) a.sign )<<15 ) | 0x7FFF;
>      return z;
>  
> @@ -449,7 +448,7 @@ 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
>  `. `'   address@hidden         | address@hidden
>    `-    people.debian.org/~aurel32 | www.aurel32.net
> 
> 
>