7 files changed, 61 insertions, 6 deletions
diff --git a/engines/gargoyle/frotz/frotz.cpp b/engines/gargoyle/frotz/frotz.cpp
index df6d7364ac..5c861890bf 100644
--- a/engines/gargoyle/frotz/frotz.cpp
+++ b/engines/gargoyle/frotz/frotz.cpp
@@ -74,6 +74,9 @@ void Frotz::initialize() {
 
 	// Call process initialization
 	Processor::initialize();
+
+	// Restart the game
+	z_restart();
 }
 
 Common::Error Frotz::loadGameState(int slot) {
diff --git a/engines/gargoyle/frotz/glk_interface.cpp b/engines/gargoyle/frotz/glk_interface.cpp
index f60ecc5009..13d0a562b5 100644
--- a/engines/gargoyle/frotz/glk_interface.cpp
+++ b/engines/gargoyle/frotz/glk_interface.cpp
@@ -26,7 +26,7 @@ namespace Gargoyle {
 namespace Frotz {
 
 GlkInterface::GlkInterface(OSystem *syst, const GargoyleGameDescription *gameDesc) :
-		Glk(syst, gameDesc), UserOptions(),
+		Glk(syst, gameDesc),
 		oldstyle(0), curstyle(0), cury(1), curx(1), fixforced(0),
 		curr_fg(-2), curr_bg(-2), curr_font(1), prev_font(1), temp_font(0),
 		curr_status_ht(0), mach_status_ht(0), gos_status(nullptr), gos_upper(nullptr),
diff --git a/engines/gargoyle/frotz/glk_interface.h b/engines/gargoyle/frotz/glk_interface.h
index 1d30364683..f02fa0dd8c 100644
--- a/engines/gargoyle/frotz/glk_interface.h
+++ b/engines/gargoyle/frotz/glk_interface.h
@@ -40,7 +40,7 @@ enum SoundEffect {
  * Implements an intermediate interface on top of the GLK layer, providing screen
  * and sound effect handling
  */
-class GlkInterface : public Glk, public UserOptions, public virtual Mem {
+class GlkInterface : public Glk, public virtual UserOptions, public virtual Mem {
 public:
 	zchar statusline[256];
 	int oldstyle;
diff --git a/engines/gargoyle/frotz/mem.cpp b/engines/gargoyle/frotz/mem.cpp
index cb5a73b8d1..d9ff53d449 100644
--- a/engines/gargoyle/frotz/mem.cpp
+++ b/engines/gargoyle/frotz/mem.cpp
@@ -112,11 +112,15 @@ void Header::loadHeader(Common::SeekableReadStream &f) {
 
 /*--------------------------------------------------------------------------*/
 
-Mem::Mem() : story_fp(nullptr), blorb_ofs(0), blorb_len(0), story_size(0) {
+Mem::Mem() : story_fp(nullptr), blorb_ofs(0), blorb_len(0), story_size(0),
+		first_undo(nullptr), last_undo(nullptr), curr_undo(nullptr),
+		undo_mem(nullptr), prev_zmp(nullptr), undo_diff(nullptr),
+		undo_count(0), reserve_mem(0) {
 }
 
 void Mem::initialize() {
 	initializeStoryFile();
+	initializeUndo();
 	loadGameHeader();
 
 	// Allocate memory for story data
@@ -173,6 +177,29 @@ void Mem::initializeStoryFile() {
 		error("This file is too small to be a Z-code file.");
 }
 
+void Mem::initializeUndo() {
+	void *reserved = nullptr;
+
+	if (reserve_mem != 0) {
+		if ((reserved = malloc(reserve_mem)) == NULL)
+			return;
+	}
+
+	// Allocate h_dynamic_size bytes for previous dynamic zmp state
+	// + 1.5 h_dynamic_size for Quetzal diff + 2.
+	undo_mem = new zbyte[(h_dynamic_size * 5) / 2 + 2];
+	if (undo_mem != nullptr) {
+		prev_zmp = undo_mem;
+		undo_diff = undo_mem + h_dynamic_size;
+		memcpy(prev_zmp, zmp, h_dynamic_size);
+	} else {
+		_undo_slots = 0;
+	}
+
+	if (reserve_mem != 0)
+		delete reserved;
+}
+
 void Mem::loadGameHeader() {
 	// Load header
 	zmp = new byte[64];
diff --git a/engines/gargoyle/frotz/mem.h b/engines/gargoyle/frotz/mem.h
index 55cc4dc6fe..e12c062ff8 100644
--- a/engines/gargoyle/frotz/mem.h
+++ b/engines/gargoyle/frotz/mem.h
@@ -82,6 +82,21 @@ enum {
 };
 
 /**
+ * Stores undo information
+ */
+struct undo_struct {
+	undo_struct *next;
+	undo_struct *prev;
+	long pc;
+	long diff_size;
+	zword frame_count;
+	zword stack_size;
+	zword frame_offset;
+	// undo diff and stack data follow
+};
+typedef undo_struct undo_t;
+
+/**
  * Story file header data
  */
 struct Header {
@@ -160,13 +175,18 @@ public:
 	void loadHeader(Common::SeekableReadStream &f);
 };
 
-class Mem : public Header {
+class Mem : public Header, public virtual UserOptions {
 protected:
 	Common::SeekableReadStream *story_fp;
 	uint blorb_ofs, blorb_len;
 	uint story_size;
 	byte *pcp;
 	byte *zmp;
+
+	undo_t *first_undo, *last_undo, *curr_undo;
+	zbyte *undo_mem, *prev_zmp, *undo_diff;
+	int undo_count;
+	int reserve_mem;
 private:
 	/**
 	 * Handles setting the story file, parsing it if it's a Blorb file
@@ -174,6 +194,11 @@ private:
 	void initializeStoryFile();
 
 	/**
+	 * Setup undo data
+	 */
+	void initializeUndo();
+
+	/**
 	 * Handles loading the game header
 	 */
 	void loadGameHeader();
diff --git a/engines/gargoyle/frotz/processor.cpp b/engines/gargoyle/frotz/processor.cpp
index 20fb387b74..721f64b4bf 100644
--- a/engines/gargoyle/frotz/processor.cpp
+++ b/engines/gargoyle/frotz/processor.cpp
@@ -132,7 +132,7 @@ Opcode Processor::ext_opcodes[64] = {
 };
 
 Processor::Processor(OSystem *syst, const GargoyleGameDescription *gameDesc) : 
-		GlkInterface(syst, gameDesc), Mem(), Errors(),
+		GlkInterface(syst, gameDesc), Errors(),
 		_finished(0), _sp(nullptr), _fp(nullptr), _frameCount(0),
 		zargc(0), _decoded(nullptr), _encoded(nullptr), _resolution(0),
 		_randomInterval(0), _randomCtr(0), first_restart(true) {
diff --git a/engines/gargoyle/frotz/processor.h b/engines/gargoyle/frotz/processor.h
index a11fa1b966..77192b4f6a 100644
--- a/engines/gargoyle/frotz/processor.h
+++ b/engines/gargoyle/frotz/processor.h
@@ -412,7 +412,7 @@ private:
 	zchar unicode_tolower(zchar c);
 
 	/**@}*/
-private:
+protected:
 	/**
 	 * \defgroup General Opcode methods
 	 * @{