bcel/generic/LocalVariableInstruction.java

/*
 * 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 org.apache.bcel.generic;

import java.io.DataOutputStream;
import java.io.IOException;

import org.apache.bcel.Const;
import org.apache.bcel.util.ByteSequence;

/**
 * Abstract super class for instructions dealing with local variables.
 *
 * @version $Id$
 */
public abstract class LocalVariableInstruction extends Instruction implements TypedInstruction,
        IndexedInstruction {

    /**
     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
     */
    @Deprecated
    protected int n = -1; // index of referenced variable

    private short c_tag = -1; // compact version, such as ILOAD_0
    private short canon_tag = -1; // canonical tag such as ILOAD


    private boolean wide() {
        return n > Const.MAX_BYTE;
    }


    /**
     * Empty constructor needed for Instruction.readInstruction.
     * Not to be used otherwise.
     * tag and length are defined in readInstruction and initFromFile, respectively.
     */
    LocalVariableInstruction(final short canon_tag, final short c_tag) {
        super();
        this.canon_tag = canon_tag;
        this.c_tag = c_tag;
    }


    /**
     * Empty constructor needed for Instruction.readInstruction.
     * Also used by IINC()!
     */
    LocalVariableInstruction() {
    }


    /**
     * @param opcode Instruction opcode
     * @param c_tag Instruction number for compact version, ALOAD_0, e.g.
     * @param n local variable index (unsigned short)
     */
    protected LocalVariableInstruction(final short opcode, final short c_tag, final int n) {
        super(opcode, (short) 2);
        this.c_tag = c_tag;
        canon_tag = opcode;
        setIndex(n);
    }


    /**
     * Dump instruction as byte code to stream out.
     * @param out Output stream
     */
    @Override
    public void dump( final DataOutputStream out ) throws IOException {
        if (wide()) {
            out.writeByte(Const.WIDE);
        }
        out.writeByte(super.getOpcode());
        if (super.getLength() > 1) { // Otherwise ILOAD_n, instruction, e.g.
            if (wide()) {
                out.writeShort(n);
            } else {
                out.writeByte(n);
            }
        }
    }


    /**
     * Long output format:
     *
     * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]"
     * "("&lt;length of instruction&gt;")" "&lt;"&lt; local variable index&gt;"&gt;"
     *
     * @param verbose long/short format switch
     * @return mnemonic for instruction
     */
    @Override
    public String toString( final boolean verbose ) {
        final short _opcode = super.getOpcode();
        if (((_opcode >= Const.ILOAD_0) && (_opcode <= Const.ALOAD_3))
         || ((_opcode >= Const.ISTORE_0) && (_opcode <= Const.ASTORE_3))) {
            return super.toString(verbose);
        }
        return super.toString(verbose) + " " + n;
    }


    /**
     * Read needed data (e.g. index) from file.
     * <pre>
     * (ILOAD &lt;= tag &lt;= ALOAD_3) || (ISTORE &lt;= tag &lt;= ASTORE_3)
     * </pre>
     */
    @Override
    protected void initFromFile( final ByteSequence bytes, final boolean wide ) throws IOException {
        if (wide) {
            n = bytes.readUnsignedShort();
            super.setLength(4);
        } else {
            final short _opcode = super.getOpcode();
            if (((_opcode >= Const.ILOAD) && (_opcode <= Const.ALOAD))
             || ((_opcode >= Const.ISTORE) && (_opcode <= Const.ASTORE))) {
                n = bytes.readUnsignedByte();
                super.setLength(2);
            } else if (_opcode <= Const.ALOAD_3) { // compact load instruction such as ILOAD_2
                n = (_opcode - Const.ILOAD_0) % 4;
                super.setLength(1);
            } else { // Assert ISTORE_0 <= tag <= ASTORE_3
                n = (_opcode - Const.ISTORE_0) % 4;
                super.setLength(1);
            }
        }
    }


    /**
     * @return local variable index (n) referred by this instruction.
     */
    @Override
    public final int getIndex() {
        return n;
    }


    /**
     * Set the local variable index.
     * also updates opcode and length
     * TODO Why?
     * @see #setIndexOnly(int)
     */
    @Override
    public void setIndex( final int n ) { // TODO could be package-protected?
        if ((n < 0) || (n > Const.MAX_SHORT)) {
            throw new ClassGenException("Illegal value: " + n);
        }
        this.n = n;
        // Cannot be < 0 as this is checked above
        if (n <= 3) { // Use more compact instruction xLOAD_n
            super.setOpcode((short) (c_tag + n));
            super.setLength(1);
        } else {
            super.setOpcode(canon_tag);
            if (wide()) {
                super.setLength(4);
            } else {
                super.setLength(2);
            }
        }
    }


    /** @return canonical tag for instruction, e.g., ALOAD for ALOAD_0
     */
    public short getCanonicalTag() {
        return canon_tag;
    }


    /**
     * Returns the type associated with the instruction -
     * in case of ALOAD or ASTORE Type.OBJECT is returned.
     * This is just a bit incorrect, because ALOAD and ASTORE
     * may work on every ReferenceType (including Type.NULL) and
     * ASTORE may even work on a ReturnaddressType .
     * @return type associated with the instruction
     */
    @Override
    public Type getType( final ConstantPoolGen cp ) {
        switch (canon_tag) {
            case Const.ILOAD:
            case Const.ISTORE:
                return Type.INT;
            case Const.LLOAD:
            case Const.LSTORE:
                return Type.LONG;
            case Const.DLOAD:
            case Const.DSTORE:
                return Type.DOUBLE;
            case Const.FLOAD:
            case Const.FSTORE:
                return Type.FLOAT;
            case Const.ALOAD:
            case Const.ASTORE:
                return Type.OBJECT;
            default:
                throw new ClassGenException("Oops: unknown case in switch" + canon_tag);
        }
    }

    /**
     * Sets the index of the referenced variable (n) only
     * @since 6.0
     * @see #setIndex(int)
     */
    final void setIndexOnly(final int n) {
        this.n = n;
    }
}