FSCALE should always return 0.0 if ST(0) input is 0.0, regardless of

value of ST(1); this might otherwise return infinity or NaN if not trapped. Fixes fade-in on MDK2.
sarah-walker-pcem · Jun 2, 2021 · 2e037b5 · 2e037b5
1 parent 0ad51dd
commit 2e037b5
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/src/x87_ops_misc.h b/src/x87_ops_misc.h
@@ -673,7 +673,8 @@ static int opFSCALE(uint32_t fetchdat)
         cpu_state.pc++;
         if (fplog) pclog("FSCALE\n");
         temp64 = (int64_t)ST(1);
-        ST(0) = ST(0) * pow(2.0, (double)temp64);
+        if (ST(0) != 0.0)
+                ST(0) = ST(0) * pow(2.0, (double)temp64);
         cpu_state.tag[cpu_state.TOP&7] = TAG_VALID;
         CLOCK_CYCLES(x87_timings.fscale);
         return 0;