target-i386: fix helper_fxtract() wrt softfloat

With softfloat it's not possible to play with the overflow of an
unsigned value to get the 0 case partially correct. Use a special case
for that. Using a division to generate an infinity is the easiest way
that works for both softfloat and softfloat-native.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 16 insertions, 7 deletions

diff --git a/target-i386/op_helper.c b/target-i386/op_helper.c
index 943d217e6e..4850c63699 100644
--- a/target-i386/op_helper.c
+++ b/target-i386/op_helper.c
@@ -4005,15 +4005,24 @@ void helper_fpatan(void)
 void helper_fxtract(void)
 {
     CPU86_LDoubleU temp;
-    unsigned int expdif;
 
     temp.d = ST0;
-    expdif = EXPD(temp) - EXPBIAS;
-    /*DP exponent bias*/
-    ST0 = expdif;
-    fpush();
-    BIASEXPONENT(temp);
-    ST0 = temp.d;
+
+    if (floatx_is_zero(ST0)) {
+        /* Easy way to generate -inf and raising division by 0 exception */
+        ST0 = floatx_div(floatx_chs(floatx_one), floatx_zero, &env->fp_status);
+        fpush();
+        ST0 = temp.d;
+    } else {
+        int expdif;
+
+        expdif = EXPD(temp) - EXPBIAS;
+        /*DP exponent bias*/
+        ST0 = int32_to_floatx(expdif, &env->fp_status);
+        fpush();
+        BIASEXPONENT(temp);
+        ST0 = temp.d;
+    }
 }
 
 void helper_fprem1(void)