From afb90fee062b0a80f3e685517381650ad0419a27 Mon Sep 17 00:00:00 2001
From: PalindromicBreadLoaf <herbthehaircut@proton.me>
Date: Thu, 24 Jul 2025 08:36:37 -0400
Subject: [PATCH] Implement a few stack instructions

---
 src/cpu.cpp | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/cpu.h   |  6 ++++++
 2 files changed, 68 insertions(+)

diff --git a/src/cpu.cpp b/src/cpu.cpp
index 0f1db53..58f1472 100644
--- a/src/cpu.cpp
+++ b/src/cpu.cpp
@@ -596,9 +596,18 @@ void CPU::ExecuteInstruction() {
         case 0x2B: PLD(); break;  // PLD
         case 0x4B: PHK(); break;  // PHK
 
+        // Push Effective Instructions
+        case 0xF4: PEA(); break;    //PEA
+        case 0xD4: PEI(); break;    //PEI
+        case 0x62: PER(); break;    //PER
+
+        // REP - Reset Status Bits
+        case 0xC2: REP(); break;
+
         // More Subroutines
         case 0x60: RTS(); break;                    // RTS
         case 0x6B: RTL(); break;                    // RTL
+        case 0x40: RTI(); break;                    // RTI
 
         // ROL - Rotate Left
         case 0x2A: ROL_Accumulator(); break;    // ROL A
@@ -4099,4 +4108,57 @@ void CPU::ROR_DirectPageX() {
     }
 
     if (D & 0xFF) cycles++;
+}
+
+void CPU::PEA() {
+    const uint16_t address = ReadWord(PC);
+    PC += 2;
+
+    PushWord(address);
+    cycles += 5;
+}
+
+void CPU::PEI() {
+    const uint8_t offset = ReadByte(PC++);
+    const uint32_t indirect_addr = D + offset;
+
+    const uint16_t effective_addr = ReadWord(indirect_addr);
+
+    PushWord(effective_addr);
+    cycles += 6;
+
+    if (D & 0xFF) cycles++;
+}
+
+void CPU::PER() {
+    const auto displacement = static_cast<int16_t>(ReadWord(PC));
+    PC += 2;
+
+    const auto effective_addr = static_cast<uint16_t>(PC + displacement);
+
+    PushWord(effective_addr);
+    cycles += 6;
+}
+
+void CPU::REP() {
+    const uint8_t mask = ReadByte(PC++);
+
+    P &= ~mask;
+
+    cycles += 3;
+}
+
+void CPU::RTI() {
+    if (emulation_mode) {
+        P = PopByte();
+        PC = PopWord();
+        cycles += 7;
+    } else {
+        // Native mode
+        P = PopByte();
+        const uint16_t pc_addr = PopWord();
+        PB = PopByte();
+        PC = (static_cast<uint32_t>(PB) << 16) | pc_addr;
+        cycles += 6;
+    }
 }
\ No newline at end of file
diff --git a/src/cpu.h b/src/cpu.h
index 411b715..346067a 100644
--- a/src/cpu.h
+++ b/src/cpu.h
@@ -327,6 +327,12 @@ public:
     void ROR_AbsoluteX();
     void ROR_DirectPage();
     void ROR_DirectPageX();
+
+    void PEA();
+    void PEI();
+    void PER();
+    void REP();
+    void RTI();
 };
 
 #endif //CPU_H