From 367a82c11d4c7f4ce4f8a8cedfd1b17b93775f53 Mon Sep 17 00:00:00 2001
From: SimoneN64 <simococo03@gmail.com>
Date: Mon, 28 Aug 2023 15:58:18 +0200
Subject: [PATCH] Cop0's Index as a union

---
 src/backend/core/registers/Cop0.cpp           | 14 ++++----
 src/backend/core/registers/Cop0.hpp           | 12 ++++++-
 .../core/registers/cop/cop0instructions.cpp   | 32 +++++++++----------
 3 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/src/backend/core/registers/Cop0.cpp b/src/backend/core/registers/Cop0.cpp
index e56c468e..dc32365f 100644
--- a/src/backend/core/registers/Cop0.cpp
+++ b/src/backend/core/registers/Cop0.cpp
@@ -19,13 +19,13 @@ void Cop0::Reset() {
   EPC = 0xFFFFFFFFFFFFFFFFll;
   ErrorEPC = 0xFFFFFFFFFFFFFFFFll;
   wired = 0;
-  index = 63;
+  index.raw = 63;
   badVaddr = 0xFFFFFFFFFFFFFFFF;
 }
 
 u32 Cop0::GetReg32(u8 addr) {
   switch(addr) {
-    case COP0_REG_INDEX: return index & 0x8000003F;
+    case COP0_REG_INDEX: return index.raw & INDEX_MASK;
     case COP0_REG_RANDOM: return GetRandom();
     case COP0_REG_ENTRYLO0: return entryLo0.raw;
     case COP0_REG_ENTRYLO1: return entryLo1.raw;
@@ -54,7 +54,7 @@ u32 Cop0::GetReg32(u8 addr) {
     case 23: case 24: case 25:
     case 31: return openbus;
     default:
-      Util::panic("Unsupported word read from COP0 register {}", index);
+      Util::panic("Unsupported word read from COP0 register {}", addr);
   }
 }
 
@@ -75,14 +75,14 @@ u64 Cop0::GetReg64(u8 addr) const {
     case 23: case 24: case 25:
     case 31: return openbus;
     default:
-      Util::panic("Unsupported dword read from COP0 register {}", index);
+      Util::panic("Unsupported dword read from COP0 register {}", addr);
   }
 }
 
 void Cop0::SetReg32(u8 addr, u32 value) {
   openbus = value & 0xFFFFFFFF;
   switch(addr) {
-    case COP0_REG_INDEX: index = value; break;
+    case COP0_REG_INDEX: index.raw = value & INDEX_MASK; break;
     case COP0_REG_RANDOM: break;
     case COP0_REG_ENTRYLO0:
       entryLo0.raw = value & ENTRY_LO_MASK;
@@ -137,7 +137,7 @@ void Cop0::SetReg32(u8 addr, u32 value) {
     case 23: case 24: case 25:
     case 31: break;
     default:
-      Util::panic("Unsupported word write from COP0 register {}", index);
+      Util::panic("Unsupported word write from COP0 register {}", addr);
   }
 }
 
@@ -352,7 +352,7 @@ void Cop0::decodeInterp(Registers& regs, u32 instr) {
     case 0x10 ... 0x1F:
       switch(mask_cop2) {
         case 0x01: tlbr(); break;
-        case 0x02: tlbw(index & 0x3F); break;
+        case 0x02: tlbw(index.i); break;
         case 0x06: tlbw(GetRandom()); break;
         case 0x08: tlbp(regs); break;
         case 0x18: eret(regs); break;
diff --git a/src/backend/core/registers/Cop0.hpp b/src/backend/core/registers/Cop0.hpp
index 4b190e9c..d9b33201 100644
--- a/src/backend/core/registers/Cop0.hpp
+++ b/src/backend/core/registers/Cop0.hpp
@@ -5,6 +5,7 @@
 namespace n64 {
 #define STATUS_MASK 0xFF57FFFF
 #define CONFIG_MASK 0x0F00800F
+#define INDEX_MASK 0x8000003F
 #define COP0_REG_INDEX 0
 #define COP0_REG_RANDOM 1
 #define COP0_REG_ENTRYLO0 2
@@ -133,6 +134,15 @@ union PageMask {
   };
 };
 
+union Index {
+  u32 raw;
+  struct {
+    unsigned i:6;
+    unsigned:25;
+    unsigned p:1;
+  };
+};
+
 struct TLBEntry {
   bool initialized;
   union {
@@ -220,7 +230,7 @@ struct Cop0 {
   PageMask pageMask{};
   EntryHi entryHi{};
   EntryLo entryLo0{}, entryLo1{};
-  u32 index{};
+  Index index{};
   Cop0Context context{};
   u32 wired{}, r7{};
   u64 badVaddr{}, count{};
diff --git a/src/backend/core/registers/cop/cop0instructions.cpp b/src/backend/core/registers/cop/cop0instructions.cpp
index 0dffe94e..e89e5e1c 100644
--- a/src/backend/core/registers/cop/cop0instructions.cpp
+++ b/src/backend/core/registers/cop/cop0instructions.cpp
@@ -32,12 +32,11 @@ void Cop0::eret(Registers& regs) {
 
 
 void Cop0::tlbr() {
-  u8 Index = index & 0b111111;
-  if (Index >= 32) {
-    Util::panic("TLBR with TLB index {}", index);
+  if (index.i >= 32) {
+    Util::panic("TLBR with TLB index {}", index.i);
   }
 
-  TLBEntry entry = tlb[Index];
+  TLBEntry entry = tlb[index.i];
 
   entryHi.raw = entry.entryHi.raw;
   entryLo0.raw = entry.entryLo0.raw & 0x3FFFFFFF;
@@ -48,34 +47,35 @@ void Cop0::tlbr() {
   pageMask.raw = entry.pageMask.raw;
 }
 
-void Cop0::tlbw(int index) {
+void Cop0::tlbw(int index_) {
   PageMask page_mask{};
   page_mask = pageMask;
   u32 top = page_mask.mask & 0xAAA;
   page_mask.mask = top | (top >> 1);
 
-  if(index >= 32) {
-    Util::panic("TLBWI with TLB index {}", index);
+  if(index_ >= 32) {
+    Util::panic("TLBWI with TLB index {}", index_);
   }
 
-  tlb[index].entryHi.raw  = entryHi.raw;
-  tlb[index].entryHi.vpn2 &= ~page_mask.mask;
+  tlb[index_].entryHi.raw  = entryHi.raw;
+  tlb[index_].entryHi.vpn2 &= ~page_mask.mask;
 
-  tlb[index].entryLo0.raw = entryLo0.raw & 0x03FFFFFE;
-  tlb[index].entryLo1.raw = entryLo1.raw & 0x03FFFFFE;
-  tlb[index].pageMask.raw = page_mask.raw;
+  tlb[index_].entryLo0.raw = entryLo0.raw & 0x03FFFFFE;
+  tlb[index_].entryLo1.raw = entryLo1.raw & 0x03FFFFFE;
+  tlb[index_].pageMask.raw = page_mask.raw;
 
-  tlb[index].global = entryLo0.g && entryLo1.g;
-  tlb[index].initialized = true;
+  tlb[index_].global = entryLo0.g && entryLo1.g;
+  tlb[index_].initialized = true;
 }
 
 void Cop0::tlbp(Registers& regs) {
   int match = -1;
   TLBEntry* entry = TLBTryMatch(regs, entryHi.raw, &match);
   if(entry && match >= 0) {
-    index = match;
+    index.i = match;
+    index.p = 0;
   } else {
-    index = 0x80000000;
+    index.p = 1;
   }
 }