fpu/softfloat: Introduce parts_is_snan_frac

Tested-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>

fpu/softfloat-specialize.h

@@ -86,6 +86,21 @@ this code that are retained.
 #define NO_SIGNALING_NANS 1
 #endif
 
+/*----------------------------------------------------------------------------
+| For the deconstructed floating-point with fraction FRAC, return true
+| if the fraction represents a signalling NaN; otherwise false.
+*----------------------------------------------------------------------------*/
+
+static bool parts_is_snan_frac(uint64_t frac, float_status *status)
+{
+#ifdef NO_SIGNALING_NANS
+    return false;
+#else
+    flag msb = extract64(frac, DECOMPOSED_BINARY_POINT - 1, 1);
+    return msb == status->snan_bit_is_one;
+#endif
+}
+
 /*----------------------------------------------------------------------------
 | The pattern for a default generated half-precision NaN.
 *----------------------------------------------------------------------------*/

fpu/softfloat.c

@@ -331,16 +331,8 @@ static FloatParts canonicalize(FloatParts part, const FloatFmt *parm,
             part.cls = float_class_inf;
         } else {
             part.frac <<= parm->frac_shift;
-#ifdef NO_SIGNALING_NANS
-            part.cls = float_class_qnan;
-#else
-            int64_t msb = part.frac << 2;
-            if ((msb < 0) == status->snan_bit_is_one) {
-                part.cls = float_class_snan;
-            } else {
-                part.cls = float_class_qnan;
-            }
-#endif
+            part.cls = (parts_is_snan_frac(part.frac, status)
+                        ? float_class_snan : float_class_qnan);
         }
     } else if (part.exp == 0) {
         if (likely(part.frac == 0)) {