[Qemu-devel] [PATCH v2] softfloat: fix floatx80_is_{quiet, signaling}_nan()

[Qemu-devel] [PATCH v2] softfloat: fix floatx80_is_{quiet, signaling}_nan()

[Aurelien Jarno]

floatx80_is_{quiet,signaling}_nan() functions are incorrectly detecting
the type of NaN, depending on SNAN_BIT_IS_ONE, one of the two is
returning the correct value, and the other true for any kind of NaN.

This patch fixes that by applying the same kind of comparison as for
other float formats, but taking into account the explicit bit.

* v1 -> v2
- fix sign of comparison
- add a comment about explicit bit

Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 fpu/softfloat-specialize.h |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index f293f24..62a980d 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -468,7 +468,8 @@ static float64 propagateFloat64NaN( float64 a, float64 b STATUS_PARAM)
 
 /*----------------------------------------------------------------------------
 | Returns 1 if the extended double-precision floating-point value `a' is a
-| quiet NaN; otherwise returns 0.
+| quiet NaN; otherwise returns 0. This slightly differs from the same
+| function for other types as floatx80 has an explicit bit.
 *----------------------------------------------------------------------------*/
 
 int floatx80_is_quiet_nan( floatx80 a )
@@ -482,19 +483,22 @@ int floatx80_is_quiet_nan( floatx80 a )
         && (bits64) ( aLow<<1 )
         && ( a.low == aLow );
 #else
-    return ( ( a.high & 0x7FFF ) == 0x7FFF ) && (bits64) ( a.low<<1 );
+    return ( ( a.high & 0x7FFF ) == 0x7FFF )
+        && (LIT64( 0x8000000000000000 ) <= ((bits64) ( a.low<<1 )));
 #endif
 }
 
 /*----------------------------------------------------------------------------
 | Returns 1 if the extended double-precision floating-point value `a' is a
-| signaling NaN; otherwise returns 0.
+| signaling NaN; otherwise returns 0. This slightly differs from the same
+| function for other types as floatx80 has an explicit bit.
 *----------------------------------------------------------------------------*/
 
 int floatx80_is_signaling_nan( floatx80 a )
 {
 #if SNAN_BIT_IS_ONE
-    return ( ( a.high & 0x7FFF ) == 0x7FFF ) && (bits64) ( a.low<<1 );
+    return ( ( a.high & 0x7FFF ) == 0x7FFF )
+        && (LIT64( 0x8000000000000000 ) <= ((bits64) ( a.low<<1 )));
 #else
     bits64 aLow;
 
-- 
1.7.2.3