From 2e037b50760c4ee35b86104e5102bbc1cb1881a5 Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Wed, 2 Jun 2021 21:13:39 +0100
Subject: [PATCH] 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.

---
 src/x87_ops_misc.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/x87_ops_misc.h b/src/x87_ops_misc.h
index bde89c78..8abb5442 100644
--- 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;