WideForm.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.commons.compress.harmony.unpack200.bytecode.forms;

import org.apache.commons.compress.harmony.unpack200.bytecode.ByteCode;
import org.apache.commons.compress.harmony.unpack200.bytecode.OperandManager;

/**
 * This class implements the byte code form for the wide instruction. Unlike other instructions, it can take multiple forms, depending on what is being widened.
 */
public class WideForm extends VariableInstructionForm {

    public WideForm(final int opcode, final String name) {
        super(opcode, name);
    }

    /*
     * (non-Javadoc)
     *
     * @see org.apache.commons.compress.harmony.unpack200.bytecode.forms.ByteCodeForm#setByteCodeOperands(org.apache.commons.
     * compress.harmony.unpack200.bytecode.ByteCode, org.apache.commons.compress.harmony.unpack200.bytecode.OperandTable,
     * org.apache.commons.compress.harmony.unpack200.SegmentConstantPool)
     */
    @Override
    public void setByteCodeOperands(final ByteCode byteCode, final OperandManager operandManager, final int codeLength) {
        final int instruction = operandManager.nextWideByteCode();
        if (instruction == 132) {
            setByteCodeOperandsFormat2(instruction, byteCode, operandManager, codeLength);
        } else {
            setByteCodeOperandsFormat1(instruction, byteCode, operandManager, codeLength);
        }
    }

    /**
     * This method sets the rewrite array for the bytecode using Format 1 of the JVM spec: an opcode and two index bytes. This is used for ?load/?store/ret
     *
     * @param instruction    should be 132
     * @param byteCode       the byte code whose rewrite array should be updated
     * @param operandManager the source of the operands
     * @param codeLength     ignored
     */
    protected void setByteCodeOperandsFormat1(final int instruction, final ByteCode byteCode, final OperandManager operandManager, final int codeLength) {

        // Even though this code is really similar to the
        // code for setByteCodeOperandsFormat2, I've left it
        // distinct here. This is so changing one will
        // not change the other - if there is a need to change,
        // there's a good chance that the formats will
        // differ, so an updater will not have to disentangle
        // it.
        final int local = operandManager.nextLocal();

        // Unlike most byte codes, the wide bytecode is a
        // variable-sized bytecode. Because of this, the
        // rewrite array has to be defined here individually
        // for each bytecode, rather than in the ByteCodeForm
        // class.

        final int[] newRewrite = new int[4];
        int rewriteIndex = 0;

        // Fill in what we can now
        // wide opcode
        newRewrite[rewriteIndex++] = byteCode.getOpcode();

        // "real" instruction that is widened
        newRewrite[rewriteIndex++] = instruction;

        // Index bytes
        setRewrite2Bytes(local, rewriteIndex, newRewrite);
        rewriteIndex += 2;

        byteCode.setRewrite(newRewrite);
    }

    /**
     * This method sets the rewrite array for the bytecode using Format 2 of the JVM spec: an opcode, two index bytes, and two constant bytes. This is used for
     * iinc.
     *
     * @param instruction    int should be 132
     * @param byteCode       ByteCode whose rewrite array should be updated
     * @param operandManager OperandManager source of the operands
     * @param codeLength     ignored
     */
    protected void setByteCodeOperandsFormat2(final int instruction, final ByteCode byteCode, final OperandManager operandManager, final int codeLength) {

        final int local = operandManager.nextLocal();
        final int constWord = operandManager.nextShort();

        // Unlike most byte codes, the wide bytecode is a
        // variable-sized bytecode. Because of this, the
        // rewrite array has to be defined here individually
        // for each bytecode, rather than in the ByteCodeForm
        // class.

        final int[] newRewrite = new int[6];
        int rewriteIndex = 0;

        // Fill in what we can now
        // wide opcode
        newRewrite[rewriteIndex++] = byteCode.getOpcode();

        // "real" instruction that is widened
        newRewrite[rewriteIndex++] = instruction;

        // Index bytes
        setRewrite2Bytes(local, rewriteIndex, newRewrite);
        rewriteIndex += 2;

        // constant bytes
        setRewrite2Bytes(constWord, rewriteIndex, newRewrite);
        rewriteIndex += 2; // not strictly necessary, but just in case
        // something comes along later

        byteCode.setRewrite(newRewrite);
    }
}