softfloat: Add float*_min() and float*_max() functions

Add min and max operations to softfloat. This allows us to implement
propagation of NaNs and handling of negative zero correctly (unlike
the approach of having target helper routines return one of the operands
based on the result of a comparison op).
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

fpu/softfloat.c

@@ -6057,6 +6057,55 @@ int float128_compare_quiet( float128 a, float128 b STATUS_PARAM )
     return float128_compare_internal(a, b, 1 STATUS_VAR);
 }
 
+/* min() and max() functions. These can't be implemented as
+ * 'compare and pick one input' because that would mishandle
+ * NaNs and +0 vs -0.
+ */
+#define MINMAX(s, nan_exp)                                              \
+INLINE float ## s float ## s ## _minmax(float ## s a, float ## s b,     \
+                                        int ismin STATUS_PARAM )        \
+{                                                                       \
+    flag aSign, bSign;                                                  \
+    uint ## s ## _t av, bv;                                             \
+    a = float ## s ## _squash_input_denormal(a STATUS_VAR);             \
+    b = float ## s ## _squash_input_denormal(b STATUS_VAR);             \
+    if (float ## s ## _is_any_nan(a) ||                                 \
+        float ## s ## _is_any_nan(b)) {                                 \
+        return propagateFloat ## s ## NaN(a, b STATUS_VAR);             \
+    }                                                                   \
+    aSign = extractFloat ## s ## Sign(a);                               \
+    bSign = extractFloat ## s ## Sign(b);                               \
+    av = float ## s ## _val(a);                                         \
+    bv = float ## s ## _val(b);                                         \
+    if (aSign != bSign) {                                               \
+        if (ismin) {                                                    \
+            return aSign ? a : b;                                       \
+        } else {                                                        \
+            return aSign ? b : a;                                       \
+        }                                                               \
+    } else {                                                            \
+        if (ismin) {                                                    \
+            return (aSign ^ (av < bv)) ? a : b;                         \
+        } else {                                                        \
+            return (aSign ^ (av < bv)) ? b : a;                         \
+        }                                                               \
+    }                                                                   \
+}                                                                       \
+                                                                        \
+float ## s float ## s ## _min(float ## s a, float ## s b STATUS_PARAM)  \
+{                                                                       \
+    return float ## s ## _minmax(a, b, 1 STATUS_VAR);                   \
+}                                                                       \
+                                                                        \
+float ## s float ## s ## _max(float ## s a, float ## s b STATUS_PARAM)  \
+{                                                                       \
+    return float ## s ## _minmax(a, b, 0 STATUS_VAR);                   \
+}
+
+MINMAX(32, 0xff)
+MINMAX(64, 0x7ff)
+
+
 /* Multiply A by 2 raised to the power N.  */
 float32 float32_scalbn( float32 a, int n STATUS_PARAM )
 {

fpu/softfloat.h

@@ -324,6 +324,8 @@ int float32_le_quiet( float32, float32 STATUS_PARAM );
 int float32_lt_quiet( float32, float32 STATUS_PARAM );
 int float32_compare( float32, float32 STATUS_PARAM );
 int float32_compare_quiet( float32, float32 STATUS_PARAM );
+float32 float32_min(float32, float32 STATUS_PARAM);
+float32 float32_max(float32, float32 STATUS_PARAM);
 int float32_is_quiet_nan( float32 );
 int float32_is_signaling_nan( float32 );
 float32 float32_maybe_silence_nan( float32 );
@@ -436,6 +438,8 @@ int float64_le_quiet( float64, float64 STATUS_PARAM );
 int float64_lt_quiet( float64, float64 STATUS_PARAM );
 int float64_compare( float64, float64 STATUS_PARAM );
 int float64_compare_quiet( float64, float64 STATUS_PARAM );
+float64 float64_min(float64, float64 STATUS_PARAM);
+float64 float64_max(float64, float64 STATUS_PARAM);
 int float64_is_quiet_nan( float64 a );
 int float64_is_signaling_nan( float64 );
 float64 float64_maybe_silence_nan( float64 );