Short0Instruction.java

/*
 * $Id: Short0Instruction.java 536 2008-02-19 06:03:27Z weiju $
 * 
 * Created on 10/03/2005
 * Copyright 2005-2008 by Wei-ju Wu
 * This file is part of The Z-machine Preservation Project (ZMPP).
 *
 * ZMPP is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ZMPP is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ZMPP.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.zmpp.instructions;

import org.zmpp.vm.Machine;

/**
 * This class represents instructions of type SHORT, 0OP.
 *
 * @author Wei-ju Wu
 * @version 1.0
 */
public class Short0Instruction extends AbstractInstruction {

    /**
     * Constructor.
     *
     * @param machineState a reference to the MachineState object
     * @param opcode the instruction's opcode
     */
    public Short0Instruction(Machine machineState, int opcode) {

        super(machineState, opcode);
    }

    /**
     * {@inheritDoc}
     */
    public void doInstruction() {

        switch (getOpcode()) {

            case Short0StaticInfo.OP_RTRUE:
                returnFromRoutine(TRUE);
                break;
            case Short0StaticInfo.OP_RFALSE:
                returnFromRoutine(FALSE);
                break;
            case Short0StaticInfo.OP_NOP:
                nextInstruction();
                break;
            case Short0StaticInfo.OP_SAVE:
                saveToStorage(getMachine().getCpu().getProgramCounter() + 1);
                break;
            case Short0StaticInfo.OP_RESTORE:

                restoreFromStorage();
                break;
            case Short0StaticInfo.OP_RESTART:
                getMachine().restart();
                break;
            case Short0StaticInfo.OP_QUIT:
                getMachine().quit();
                break;
            case Short0StaticInfo.OP_RET_POPPED:
                returnFromRoutine(getCpu().getVariable(0));
                break;
            case Short0StaticInfo.OP_POP:
                if (getStoryFileVersion() < 5) {
                    pop();
                } else {
                    z_catch();
                }
                break;
            case Short0StaticInfo.OP_NEW_LINE:
                getMachine().getOutput().newline();
                nextInstruction();
                break;
            case Short0StaticInfo.OP_SHOW_STATUS:

                getMachine().updateStatusLine();
                nextInstruction();
                break;
            case Short0StaticInfo.OP_VERIFY:
                branchOnTest(getMachine().getGameData().hasValidChecksum());
                break;
            case Short0StaticInfo.OP_PIRACY:
                branchOnTest(true);
                break;
            default:
                throwInvalidOpcode();
        }
    }

    /**
     * {@inheritDoc}
     */
    public InstructionForm getInstructionForm() {
        return InstructionForm.SHORT;
    }

    /**
     * {@inheritDoc}
     */
    public OperandCount getOperandCount() {
        return OperandCount.C0OP;
    }

    /**
     * {@inheritDoc}
     */
    protected InstructionStaticInfo getStaticInfo() {

        return Short0StaticInfo.getInstance();
    }

    private void pop() {

        getCpu().getVariable(0);
        nextInstruction();
    }

    private void z_catch() {

        // Stores the index of the current stack frame
        storeResult((short) (getCpu().getRoutineContexts().size() - 1));
        nextInstruction();
    }
}