/*

 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.

 */

/*

 * Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You under the Apache License, Version 2.0

 * (the "License"); you may not use this file except in compliance with

 * the License.  You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.sun.org.apache.xalan.internal.xsltc.compiler.util;

import java.io.DataOutputStream;

import java.io.IOException;

import com.sun.org.apache.bcel.internal.Const;

import com.sun.org.apache.bcel.internal.generic.ConstantPoolGen;

import com.sun.org.apache.bcel.internal.generic.Instruction;

import com.sun.org.apache.bcel.internal.generic.Visitor;

/**

 * A special abstract dummy subclass of

 * {@link org.apache.bcel.generic.Instruction} used to mark locations of

 * interest in an {@link com.sun.org.apache.bcel.internal.generic.InstructionList}.  It and

 * its subclasses are only used as placeholders, and do not contribute to the

 * actual byte code instruction stream.

 */

abstract class MarkerInstruction extends Instruction {

    /**

     * Zero-argument constructor.  Sets the opcode to an invalid value and

     * sets the length to zero, as it will not be written as part of the

     * generated byte code.

     */

    public MarkerInstruction() {

        super(Const.UNDEFINED, (short) 0);

    }

    /**

     * {@link com.sun.org.apache.bcel.internal.generic.Visitor}s will know nothing about this

     * kind of {@link org.apche.bcel.generic.Instruction}, so this method does

     * nothing.

     */

    public void accept(Visitor v) {

    }

    /**

     * The number of JVM stack entries consumed by the instruction.

     * This instruction is just a place holder, so it does not consume any

     * stack entries.

     * @param cpg The {@link com.sun.org.apache.bcel.internal.generic.ConstantPoolGen} for the

     * current {@link com.sun.org.apache.bcel.internal.generic.ClassGen}

     * @return <code>0</code> always

     */

    final public int consumeStack(ConstantPoolGen cpg) {

        return 0;

    }

    /**

     * The number of JVM stack entries produced by the instruction.

     * This instruction is just a place holder, so it does not produce any

     * stack entries.

     * @param cpg The {@link com.sun.org.apache.bcel.internal.generic.ConstantPoolGen} for the

     * current {@link com.sun.org.apache.bcel.internal.generic.ClassGen}

     * @return <code>0</code> always

     */

    final public int produceStack(ConstantPoolGen cpg) {

        return 0;

    }

    /**

     * Produce a copy of the instruction.  By default a

     * {@link MarkerInstruction} has no parameters, so the base implementation

     * of {@link #copy()} returns the instruction itself.

     * @return The instruction itself.

     */

    public Instruction copy() {

        return this;

    }

    /**

     * Dump instruction as byte code to stream out.  A {@link MarkerInstruction}

     * has no effect on the generated byte code so it is never emitted to the

     * output stream.

     * @param out Output stream

     */

    final public void dump(DataOutputStream out) throws IOException {

    }

}