GLK: ADVSYS: Created dedicated function pointer class, cleanup method opcodes

2 files changed, 81 insertions, 27 deletions

diff --git a/engines/glk/advsys/vm.cpp b/engines/glk/advsys/vm.cpp
index a06cd28512..dbfe0ad3a1 100644
--- a/engines/glk/advsys/vm.cpp
+++ b/engines/glk/advsys/vm.cpp
@@ -83,7 +83,7 @@ OpcodeMethod VM::_METHODS[0x34] = {
 };
 
 VM::VM(OSystem *syst, const GlkGameDescription &gameDesc) : GlkInterface(syst, gameDesc), Game(),
-	_pc(0), _fp(-1), _status(IN_PROGRESS) {
+		_fp(_stack), _pc(0), _status(IN_PROGRESS) {
 }
 
 ExecutionResult VM::execute(int offset) {
@@ -263,21 +263,21 @@ void VM::opRETURN() {
 		_fp = _stack.pop();
 		_pc = _stack.pop();
 
-		int varsSize = _stack.pop();
-		_stack.resize(_stack.size() - varsSize);
+		int argsSize = _stack.pop();
+		_stack.resize(_stack.size() - argsSize);
 		_stack.top() = val;
 	}
 }
 
 void VM::opCALL() {
-	int varSize = readCodeByte();
-	int topIndex = _stack.size() - 1;
+	int argsSize = readCodeByte();
 
-	_stack.push(varSize);
+	_stack.push(argsSize);
 	_stack.push(_pc);
 	_stack.push(_fp);
-	_fp = _stack.size();
-	_pc = getActionField(_stack[topIndex - varSize], A_CODE);
+
+	_fp.set();
+	_pc = getActionField(_fp[_fp[FP_ARGS_SIZE] + FP_ARGS], A_CODE);
 }
 
 void VM::opSVAR() {
@@ -285,7 +285,7 @@ void VM::opSVAR() {
 }
 
 void VM::opSSET() {
-	setVariable(getCodeByte(), _stack.top());
+	setVariable(readCodeByte(), _stack.top());
 }
 
 void VM::opSPLIT() {
@@ -328,8 +328,6 @@ void VM::opASET() {
 }
 
 void VM::opTMP() {
-	int val = readCodeByte();
-
 }
 
 void VM::opTSET() {
@@ -357,21 +355,19 @@ void VM::opRNDMIZE() {
 }
 
 void VM::opSEND() {
-	int varSize = readCodeByte();
-	int topIndex = _stack.size() - 1;
-
-	_stack.push(varSize);
+	int argsSize = readCodeByte();
+	_stack.push(argsSize);
 	_stack.push(_pc);
 	_stack.push(_fp);
-	_fp = _stack.size();
+	_fp.set();
 
-	int val = _stack[topIndex - varSize];
+	int val = _fp[_fp[FP_ARGS_SIZE] + FP_ARGS];
 	if (val)
 		val = getObjectField(val, O_CLASS);
 	else
-		val = _stack[topIndex - varSize + 1];
+		val = _fp[_fp[FP_ARGS_SIZE] + FP_ARGS];
 
-	if (val && (val = getObjectProperty(val, _stack[topIndex - varSize + 2])) != 0) {
+	if (val && (val = getObjectProperty(val, _fp[_fp[FP_ARGS_SIZE] + 1])) != 0) {
 		_pc = getActionField(val, A_CODE);
 	} else {
 		// Return NIL if there's no action for the given message
diff --git a/engines/glk/advsys/vm.h b/engines/glk/advsys/vm.h
index e5432d3f0a..e7477b9f1b 100644
--- a/engines/glk/advsys/vm.h
+++ b/engines/glk/advsys/vm.h
@@ -103,26 +103,84 @@ enum Opcode {
 	OP_XNLIT   = 0xC0           ///< Extra short load a negative literal
 };
 
+/**
+ * Indexes useable in function pointer array offsets
+ */
+enum FPOffset {
+	FP_FP = 0,
+	FP_PC = 1,
+	FP_ARGS_SIZE = 2,
+	FP_ARGS = 3
+};
+
 class VM;
 typedef void (VM::*OpcodeMethod)();
 
 /**
+ * Fixed stack
+ */
+class FixedStack : public Common::FixedStack<int, 500> {
+public:
+	void resize(size_t newSize) {
+		assert(newSize <= _size);
+		_size = newSize;
+	}
+};
+
+/**
+ * Implements a function pointer reference into the stack. It also allows
+ * positive array indexing to reference the following:
+ *		0  = Previous function pointer
+ *		1  = Return PC
+ *		2  = Size of argument block
+ *		3+ = Any function call arguments
+ */
+class FunctionPointer {
+private:
+	FixedStack &_stack;
+	int _index;
+public:
+	/**
+	 * Constructor
+	 */
+	FunctionPointer(FixedStack &s) : _stack(s), _index(-1) {}
+
+	/**
+	 * Array indexing
+	 */
+	int &operator[](int idx) { return _stack[_index - idx - 1]; }
+
+	/**
+	 * Sets the index in the stack of the function pointer
+	 */
+	FunctionPointer &operator=(int index) {
+		_index = index;
+		return *this;
+	}
+
+	/**
+	 * Returns the index in the stack of the function pointer
+	 */
+	operator int() const { return _index; }
+
+	/**
+	 * Sets the function pointer to the top of the stack
+	 */
+	void set() {
+		_index = _stack.size();
+	}
+};
+
+/**
  * Main VM for AdvSys
  */
 class VM : public GlkInterface, public Game {
-	class FixedStack : public Common::FixedStack<int, 500> {
-	public:
-		void resize(size_t newSize) {
-			assert(newSize <= _size);
-			_size = newSize;
-		}
-	};
 private:
 	static OpcodeMethod _METHODS[0x34];
 	int _pc;
 	ExecutionResult _status;
 	FixedStack _stack;
-	int _fp;
+	FunctionPointer _fp;
 private:
 	/**
 	 * Execute a single opcode within the script