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

[Aurelien Jarno]

Hi all,

The current softfloat implementation changes qNaN into sNaN when 
converting between formats, for no reason. The attached patch fixes
that. 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