From 0a9a1e5d4cb30725fe7144f9a09ff9b0b6bd8560 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <98398945+AdrianConlon@users.noreply.github.com>
Date: Sun, 7 Jan 2024 16:20:58 +0000
Subject: [PATCH] Complete all the undocumente M6502 features.  Hurrah!

---
 M6502/inc/mos6502.h   | 12 ++++++++++++
 M6502/src/mos6502.cpp | 15 +++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/M6502/inc/mos6502.h b/M6502/inc/mos6502.h
index 9ac11ba..876a795 100644
--- a/M6502/inc/mos6502.h
+++ b/M6502/inc/mos6502.h
@@ -174,6 +174,12 @@ namespace EightBit {
 			BUS().ADDRESS() = address;
 		}
 
+		void maybe_fixup(const register16_t address, const uint8_t unfixed_page) noexcept {
+			if (address.high != unfixed_page)
+				fixup(address, unfixed_page);
+		}
+
+
 		// Status flag operations
 		
 		constexpr void set_flag(int which, int condition) noexcept { P() = setBit(P(), which, condition); }
@@ -306,6 +312,12 @@ namespace EightBit {
 		void sha_AbsoluteY() noexcept;
 		void sha_IndirectIndexedY() noexcept;
 
+		// TAS
+		void tas_AbsoluteY() noexcept;
+
+		// LAS
+		void las_AbsoluteY() noexcept;
+
 		// SYA
 		void sya_AbsoluteX() noexcept;
 
diff --git a/M6502/src/mos6502.cpp b/M6502/src/mos6502.cpp
index 98ab8c5..2140faa 100644
--- a/M6502/src/mos6502.cpp
+++ b/M6502/src/mos6502.cpp
@@ -292,7 +292,7 @@ int EightBit::MOS6502::execute() noexcept {
 	case 0x98:	swallow(); A() = through(Y());								break;	// TYA (implied)
 	case 0x99:	sta_AbsoluteY();											break;	// STA (absolute, Y)
 	case 0x9a:	swallow(); S() = X();										break;	// TXS (implied)
-	case 0x9b:																break;
+	case 0x9b:	tas_AbsoluteY();											break;	// *TAS (absolute, Y)
 	case 0x9c:	sya_AbsoluteX();											break;  // *SYA (absolute, X)
 	case 0x9d:	sta_AbsoluteX();											break;	// STA (absolute, X)
 	case 0x9e:	sxa_AbsoluteY();											break;  // *SXA (absolute, Y)
@@ -325,7 +325,7 @@ int EightBit::MOS6502::execute() noexcept {
 	case 0xb8:	swallow(); reset_flag(VF);									break;	// CLV (implied)
 	case 0xb9:	A() = through(AM_AbsoluteY());								break;	// LDA (absolute, Y)
 	case 0xba:	swallow(); X() = through(S());								break;	// TSX (implied)
-	case 0xbb:																break;
+	case 0xbb:	las_AbsoluteY();											break;	// *LAS (absolute, Y)
 	case 0xbc:	Y() = through(AM_AbsoluteX());								break;	// LDY (absolute, X)
 	case 0xbd:	A() = through(AM_AbsoluteX());								break;	// LDA (absolute, X)
 	case 0xbe:	X() = through(AM_AbsoluteY());								break;	// LDX (absolute, Y)
@@ -891,6 +891,17 @@ void EightBit::MOS6502::sya_AbsoluteX() noexcept {
 	memoryWrite(Y() & (address.high + 1));
 }
 
+void EightBit::MOS6502::tas_AbsoluteY() noexcept {
+	S() = A() & X();
+	sha_AbsoluteY();
+}
+
+void EightBit::MOS6502::las_AbsoluteY() noexcept {
+	const auto [address, page] = Address_AbsoluteY();
+	maybe_fixup(address, page);
+	A() = X() = S() = through(memoryRead(address) & S());
+}
+
 void EightBit::MOS6502::sxa_AbsoluteY() noexcept {
 	const auto [address, page] = Address_AbsoluteY();
 	fixup(address, page);