/**
   * 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");
    }
  }
  /**
   * Here Starts the code of a function according to the given function name that has the given
   * number of local variables.
   *
   * @param numberOfLocals The number of local variables
   */
  public void function(short numberOfLocals) throws ProgramException {

    short newSP = (short) (getSP() + numberOfLocals);
    checkSP(newSP);
    workingStackSegment.setStartAddress(newSP);

    // disable non relevant range of the local segment - enable only the number
    // of locals of this function.
    localSegment.setEnabledRange(getSP(), newSP - 1, true);

    for (int i = 0; i < numberOfLocals; i++) {
      pushValue(MAIN_STACK, (short) 0);
    }

    String functionName = currentInstruction.getStringArg();

    // adds the new function to the top of the call stack.
    callStack.pushFunction(functionName);

    // sets the static segment range
    setStaticRange(functionName);
  }