/**
   * Calls a function according to the given function number stating that the given number of
   * arguments have been pushed onto the stack
   *
   * <p>If callerIsBuiltIn then the caller is a builtIn function that called this function through
   * callFunctionFromBuiltIn. If address is -1 then a native function should be looked up and
   * called.
   */
  public void callFunction(
      short address, short numberOfArguments, String functionName, boolean callerIsBuiltIn)
      throws ProgramException {
    stackFrames.addElement(new Integer(workingStackSegment.getStartAddress()));
    workingStackSegment.setStartAddress(getSP() + 5);

    if (callerIsBuiltIn) {
      pushValue(MAIN_STACK, VMProgram.BUILTIN_FUNCTION_ADDRESS);
    } else {
      pushValue(MAIN_STACK, program.getPC());
    }
    pushFromRAM(MAIN_STACK, Definitions.LOCAL_POINTER_ADDRESS);
    pushFromRAM(MAIN_STACK, Definitions.ARG_POINTER_ADDRESS);
    pushFromRAM(MAIN_STACK, Definitions.THIS_POINTER_ADDRESS);
    pushFromRAM(MAIN_STACK, Definitions.THAT_POINTER_ADDRESS);
    ram.setValueAt(
        Definitions.ARG_POINTER_ADDRESS, (short) (getSP() - numberOfArguments - 5), false);
    ram.setValueAt(Definitions.LOCAL_POINTER_ADDRESS, getSP(), false);

    // enable in the arg segment only the number of args that were sent to the called function.
    argSegment.setEnabledRange(
        argSegment.getStartAddress(), argSegment.getStartAddress() + numberOfArguments - 1, true);

    if (address == VMProgram.BUILTIN_FUNCTION_ADDRESS) {
      // Perform some actions normally done in the function() method
      localSegment.setEnabledRange(
          localSegment.getStartAddress(),
          localSegment.getStartAddress() - 1,
          true); // no local variables
      callStack.pushFunction(functionName + " (built-in)");
      staticSegment.setEnabledRange(0, -1, true); // empty static segment
      // Read parameters from the stack
      short[] params = new short[numberOfArguments];
      for (int i = 0; i < numberOfArguments; ++i) {
        params[i] = argSegment.getValueAt(i);
      }
      // Call the built-in implementation
      builtInFunctionsRunner.callBuiltInFunction(functionName, params);
    } else if (address >= 0 || address < program.getSize()) {
      program.setPC(address);
      program.setPC(address); // make sure previouspc isn't pc-1
      // which might happen if the calling
      // function called this function in the
      // last line before the "return" and
      // was declared just before this function.
      // In this case encountering the "function"
      // command will issue an error about
      // "missing return"...
    } else {
      error("Illegal call address");
    }
  }
 /**
  * Calls a function according to the given function name with the given parameters from a built-in
  * function
  */
 public void callFunctionFromBuiltIn(String functionName, short[] params) throws ProgramException {
   // Push the arguments onto the stack
   for (int i = 0; i < params.length; ++i) {
     pushValue(METHOD_STACK, params[i]);
   }
   callFunction(program.getAddress(functionName), (short) params.length, functionName, true);
 }
  /** Sets the static segment range according to the the given function (file) name. */
  protected void setStaticRange(String functionName) throws ProgramException {
    int dotLocation = functionName.indexOf(".");
    if (dotLocation == -1) throw new ProgramException("Illegal function name: " + functionName);

    String className = functionName.substring(0, dotLocation);
    int[] range = program.getStaticRange(className);
    if (range == null)
      throw new ProgramException("Function name doesn't match class name: " + functionName);

    staticSegment.setStartAddress(range[0]);
    staticSegment.setEnabledRange(range[0], range[1], true);
  }
  /**
   * Constructs the CPU with given program, RAM, call stack, bus, stack and other memory segments.
   */
  public CPU(
      VMProgram program,
      RAM ram,
      CallStack callStack,
      Calculator calculator,
      Bus bus,
      AbsolutePointedMemorySegment stackSegment,
      TrimmedAbsoluteMemorySegment workingStackSegment,
      MemorySegment staticSegment,
      MemorySegment localSegment,
      MemorySegment argSegment,
      MemorySegment thisSegment,
      MemorySegment thatSegment,
      MemorySegment tempSegment,
      File builtInDir) {
    this.program = program;
    this.ram = ram;
    this.callStack = callStack;
    this.calculator = calculator;
    this.bus = bus;

    this.stackSegment = stackSegment;
    this.workingStackSegment = workingStackSegment;
    this.staticSegment = staticSegment;
    this.localSegment = localSegment;
    this.argSegment = argSegment;
    this.thisSegment = thisSegment;
    this.thatSegment = thatSegment;
    this.tempSegment = tempSegment;

    segments = new MemorySegment[HVMInstructionSet.NUMBER_OF_ACTUAL_SEGMENTS];
    segments[HVMInstructionSet.LOCAL_SEGMENT_CODE] = localSegment;
    segments[HVMInstructionSet.ARG_SEGMENT_CODE] = argSegment;
    segments[HVMInstructionSet.THIS_SEGMENT_CODE] = thisSegment;
    segments[HVMInstructionSet.THAT_SEGMENT_CODE] = thatSegment;
    segments[HVMInstructionSet.TEMP_SEGMENT_CODE] = tempSegment;

    stackFrames = new Vector();

    if (program.getGUI() != null) {
      builtInFunctionsRunner = new BuiltInFunctionsRunner(this, builtInDir);
    }
  }
  /** Returns the value of the function to the top of the stack. */
  public void returnFromFunction() throws ProgramException {

    // make sure that there's somewhere to return to (old local <> 0)
    if (stackSegment.getValueAt(Definitions.LOCAL_POINTER_ADDRESS) == 0)
      throw new ProgramException(
          "Nowhere to return to in "
              + getCallStack().getTopFunction()
              + "."
              + getCurrentInstruction().getIndexInFunction());

    // done in order to clear the method stack's contents
    workingStackSegment.setStartAddress(getSP());

    bus.send(ram, Definitions.LOCAL_POINTER_ADDRESS, ram, Definitions.R13_ADDRESS); // R13 = lcl
    bus.send(
        stackSegment,
        stackSegment.getValueAt(Definitions.LOCAL_POINTER_ADDRESS) - 5,
        ram,
        Definitions.R14_ADDRESS); // R14 = return address
    bus.send(
        stackSegment,
        getSP() - 1,
        stackSegment,
        ram.getValueAt(Definitions.ARG_POINTER_ADDRESS)); // *arg = return value
    setSP((short) (ram.getValueAt(Definitions.ARG_POINTER_ADDRESS) + 1)); // SP = arg + 1
    bus.send(
        stackSegment,
        ram.getValueAt(Definitions.R13_ADDRESS) - 1,
        ram,
        Definitions.THAT_POINTER_ADDRESS); // that = *(R13 - 1)
    bus.send(
        stackSegment,
        ram.getValueAt(Definitions.R13_ADDRESS) - 2,
        ram,
        Definitions.THIS_POINTER_ADDRESS); // this = *(R13 - 2)
    bus.send(
        stackSegment,
        ram.getValueAt(Definitions.R13_ADDRESS) - 3,
        ram,
        Definitions.ARG_POINTER_ADDRESS); // arg = *(R13 - 3)
    bus.send(
        stackSegment,
        ram.getValueAt(Definitions.R13_ADDRESS) - 4,
        ram,
        Definitions.LOCAL_POINTER_ADDRESS); // lcl = *(R13 - 4)

    // removes the top function from the call stack
    callStack.popFunction();

    // check whether there is a "calling frame"
    if (stackFrames.size() > 0) {
      // retrieve stack frame address of old function
      int frameAddress = ((Integer) stackFrames.lastElement()).intValue();
      stackFrames.removeElementAt(stackFrames.size() - 1);
      workingStackSegment.setStartAddress(frameAddress);

      // disable non relevant range of the local segment - enable only the locals
      // of the function that we returned to.
      localSegment.setEnabledRange(
          Math.max(localSegment.getStartAddress(), Definitions.STACK_START_ADDRESS),
          frameAddress - 1,
          true);

      // enable in the arg segment only the number of args that were sent to the function
      // that we returned to.
      argSegment.setEnabledRange(
          argSegment.getStartAddress(), localSegment.getStartAddress() - 6, true);

      // enable this, that according to their retrieved pointers
      thisSegment.setEnabledRange(
          Math.max(thisSegment.getStartAddress(), Definitions.HEAP_START_ADDRESS),
          Definitions.HEAP_END_ADDRESS,
          true);
      thatSegment.setEnabledRange(
          Math.max(thatSegment.getStartAddress(), Definitions.HEAP_START_ADDRESS),
          Definitions.SCREEN_END_ADDRESS,
          true);
    } /* else {
      	error("Nowhere to return to");
      } */
    // Allow return if we previously had "function" even with no call -
    // For the SimpleFunction test

    short returnAddress = ram.getValueAt(Definitions.R14_ADDRESS);
    if (returnAddress == VMProgram.BUILTIN_FUNCTION_ADDRESS) {
      staticSegment.setEnabledRange(0, -1, true); // empty static segment
      builtInFunctionsRunner.returnToBuiltInFunction(popValue(METHOD_STACK));
    } else if (returnAddress >= 0 && returnAddress < program.getSize()) {
      // sets the static segment range
      if (stackFrames.size() > 0) {
        setStaticRange(callStack.getTopFunction());
      } else {
        staticSegment.setStartAddress(Definitions.VAR_START_ADDRESS);
        staticSegment.setEnabledRange(
            Definitions.VAR_START_ADDRESS, Definitions.VAR_END_ADDRESS - 1, true);
      }
      program.setPC((short) (returnAddress - 1)); // set previousPC correctly
      program.setPC(returnAddress); // pc = *sp
    } else {
      error("Illegal return address");
    }
  }
 /**
  * Enters an infinite loop requested by a built-in function, de-facto halting the program.
  * important so that tests and other scripts finish counting (since a built-in infinite loop
  * doesn't count as steps). also needed because there is no good way to use the stop button to
  * stop an infinite loop in a built-in jack class. A message containing information may be
  * provided (can be null).
  */
 public void infiniteLoopFromBuiltIn(String message) {
   program.setPCToInfiniteLoopForBuiltIns(message);
 }
 /** Pops a value from the stack and goes to the given address if the value is not zero. */
 public void ifGoTo(short address) throws ProgramException {
   if (popAndReturn() != 0) {
     program.setPC(address);
   }
 }
 /** Goes to the label at the given address */
 public void goTo(short address) {
   program.setPC(address);
 }
  /**
   * Executes the current instruction (Program at pc). Returns false if END command, true otherwise.
   */
  public void executeInstruction() throws ProgramException {
    currentInstruction = program.getNextInstruction();

    if (currentInstruction == null) throw new ProgramException("No more instructions to execute");

    switch (currentInstruction.getOpCode()) {
      case HVMInstructionSet.ADD_CODE:
        add();
        break;
      case HVMInstructionSet.SUBSTRACT_CODE:
        substract();
        break;
      case HVMInstructionSet.NEGATE_CODE:
        negate();
        break;
      case HVMInstructionSet.EQUAL_CODE:
        equal();
        break;
      case HVMInstructionSet.GREATER_THAN_CODE:
        greaterThan();
        break;
      case HVMInstructionSet.LESS_THAN_CODE:
        lessThan();
        break;
      case HVMInstructionSet.AND_CODE:
        and();
        break;
      case HVMInstructionSet.OR_CODE:
        or();
        break;
      case HVMInstructionSet.NOT_CODE:
        not();
        break;

      case HVMInstructionSet.PUSH_CODE:
        push(currentInstruction.getArg0(), currentInstruction.getArg1());
        break;
      case HVMInstructionSet.POP_CODE:
        pop(currentInstruction.getArg0(), currentInstruction.getArg1());
        break;

      case HVMInstructionSet.GOTO_CODE:
        goTo(currentInstruction.getArg0());
        break;
      case HVMInstructionSet.IF_GOTO_CODE:
        ifGoTo(currentInstruction.getArg0());
        break;

      case HVMInstructionSet.FUNCTION_CODE:
        if (program.getCurrentPC() == program.getPreviousPC() + 1)
          throw new ProgramException("Missing return in " + callStack.getTopFunction());

        function(currentInstruction.getArg0());
        break;
      case HVMInstructionSet.RETURN_CODE:
        returnFromFunction();
        break;
      case HVMInstructionSet.CALL_CODE:
        callFunction(
            currentInstruction.getArg0(),
            currentInstruction.getArg1(),
            currentInstruction.getStringArg(),
            false);
        break;
    }
  }