From 5328e9eb10b2abeaf303310b06b37269d79dde12 Mon Sep 17 00:00:00 2001
From: Exzap <13877693+Exzap@users.noreply.github.com>
Date: Fri, 26 Jul 2024 05:13:45 +0200
Subject: [PATCH] CPU: Fix overflow bit calculation in SUBFO instruction

Since rD can overlap with rA or rB the result needs to be stored in a temporary
---
 src/Cafe/HW/Espresso/Interpreter/PPCInterpreterALU.hpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/Cafe/HW/Espresso/Interpreter/PPCInterpreterALU.hpp b/src/Cafe/HW/Espresso/Interpreter/PPCInterpreterALU.hpp
index ed97288d..fe9316f0 100644
--- a/src/Cafe/HW/Espresso/Interpreter/PPCInterpreterALU.hpp
+++ b/src/Cafe/HW/Espresso/Interpreter/PPCInterpreterALU.hpp
@@ -212,11 +212,12 @@ static void PPCInterpreter_SUBF(PPCInterpreter_t* hCPU, uint32 opcode)
 
 static void PPCInterpreter_SUBFO(PPCInterpreter_t* hCPU, uint32 opcode)
 {
-	// untested (Don't Starve Giant Edition uses this)
+	// Seen in Don't Starve Giant Edition and Teslagrad
 	// also used by DS Virtual Console (Super Mario 64 DS)
 	PPC_OPC_TEMPL3_XO();
-	hCPU->gpr[rD] = ~hCPU->gpr[rA] + hCPU->gpr[rB] + 1;
-	PPCInterpreter_setXerOV(hCPU, checkAdditionOverflow(~hCPU->gpr[rA], hCPU->gpr[rB], hCPU->gpr[rD]));
+	uint32 result = ~hCPU->gpr[rA] + hCPU->gpr[rB] + 1;
+	PPCInterpreter_setXerOV(hCPU, checkAdditionOverflow(~hCPU->gpr[rA], hCPU->gpr[rB], result));
+	hCPU->gpr[rD] = result;
 	if (opHasRC())
 		ppc_update_cr0(hCPU, hCPU->gpr[rD]);
 	PPCInterpreter_nextInstruction(hCPU);