[Qemu-devel] [PATCH v2 1/2] softfloat: fix {min, max}nummag for same-abs-value inputs

["Alex Bennée" <alex.bennee@linaro.org>]

From: "Emilio G. Cota" <cota@braap.org>

Before 8936006 ("fpu/softfloat: re-factor minmax", 2018-02-21),
we used to return +Zero for maxnummag(-Zero,+Zero); after that
commit, we return -Zero.

Fix it by making {min,max}nummag consistent with {min,max}num,
deferring to the latter when the absolute value of the operands
is the same.

With this fix we now pass fp-test.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 fpu/softfloat.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index b46dccc63e..9b99aa6ec8 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1704,7 +1704,6 @@ static FloatParts minmax_floats(FloatParts a, FloatParts b, bool ismin,
         return pick_nan(a, b, s);
     } else {
         int a_exp, b_exp;
-        bool a_sign, b_sign;
 
         switch (a.cls) {
         case float_class_normal:
@@ -1735,20 +1734,22 @@ static FloatParts minmax_floats(FloatParts a, FloatParts b, bool ismin,
             break;
         }
 
-        a_sign = a.sign;
-        b_sign = b.sign;
-        if (ismag) {
-            a_sign = b_sign = 0;
+        if (ismag && (a_exp != b_exp || a.frac != b.frac)) {
+            bool a_less = a_exp < b_exp;
+            if (a_exp == b_exp) {
+                a_less = a.frac < b.frac;
+            }
+            return a_less ^ ismin ? b : a;
         }
 
-        if (a_sign == b_sign) {
+        if (a.sign == b.sign) {
             bool a_less = a_exp < b_exp;
             if (a_exp == b_exp) {
                 a_less = a.frac < b.frac;
             }
-            return a_sign ^ a_less ^ ismin ? b : a;
+            return a.sign ^ a_less ^ ismin ? b : a;
         } else {
-            return a_sign ^ ismin ? b : a;
+            return a.sign ^ ismin ? b : a;
         }
     }
 }
-- 
2.17.0