softfloat: Add flag specific to Inf - Inf

PowerPC has this flag, and it's easier to compute it here
than after the fact.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211119160502.17432-3-richard.henderson@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

fpu/softfloat-parts.c.inc

@@ -354,7 +354,7 @@ static FloatPartsN *partsN(addsub)(FloatPartsN *a, FloatPartsN *b,
                 return a;
             }
             /* Inf - Inf */
-            float_raise(float_flag_invalid, s);
+            float_raise(float_flag_invalid | float_flag_invalid_isi, s);
             parts_default_nan(a, s);
             return a;
         }
@@ -494,6 +494,7 @@ static FloatPartsN *partsN(muladd)(FloatPartsN *a, FloatPartsN *b,
 
         if (ab_mask & float_cmask_inf) {
             if (c->cls == float_class_inf && a->sign != c->sign) {
+                float_raise(float_flag_invalid | float_flag_invalid_isi, s);
                 goto d_nan;
             }
             goto return_inf;

include/fpu/softfloat-types.h

@@ -152,6 +152,7 @@ enum {
     float_flag_inexact         = 0x0010,
     float_flag_input_denormal  = 0x0020,
     float_flag_output_denormal = 0x0040,
+    float_flag_invalid_isi     = 0x0080,  /* inf - inf */
 };
 
 /*