001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one or more
003 *  contributor license agreements.  See the NOTICE file distributed with
004 *  this work for additional information regarding copyright ownership.
005 *  The ASF licenses this file to You under the Apache License, Version 2.0
006 *  (the "License"); you may not use this file except in compliance with
007 *  the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 */
017package org.apache.commons.compress.harmony.unpack200.bytecode.forms;
018
019/**
020 * This abstract class implements the common code for instructions which have variable lengths. This is currently the
021 * *switch instructions and some wide (_w) instructions.
022 */
023public abstract class VariableInstructionForm extends ByteCodeForm {
024
025    public VariableInstructionForm(final int opcode, final String name) {
026        super(opcode, name);
027    }
028
029    /**
030     * This method writes operand directly into the rewrite array at index position specified.
031     *
032     * @param operand value to write
033     * @param absPosition position in array to write. Note that this is absolute position in the array, so one can
034     *        overwrite the bytecode if one isn't careful.
035     * @param rewrite array to write into
036     */
037    public void setRewrite2Bytes(final int operand, final int absPosition, final int[] rewrite) {
038        if (absPosition < 0) {
039            throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
040        }
041
042        final int byteCodeRewriteLength = rewrite.length;
043
044        if (absPosition + 1 > byteCodeRewriteLength) {
045            throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition
046                + " but this won't fit in the rewrite array");
047        }
048
049        rewrite[absPosition] = (0xFF00 & operand) >> 8;
050        rewrite[absPosition + 1] = 0x00FF & operand;
051    }
052
053    /**
054     * This method writes operand directly into the rewrite array at index position specified.
055     *
056     * @param operand value to write
057     * @param absPosition position in array to write. Note that this is absolute position in the array, so one can
058     *        overwrite the bytecode if one isn't careful.
059     * @param rewrite array to write into
060     */
061    public void setRewrite4Bytes(final int operand, final int absPosition, final int[] rewrite) {
062        if (absPosition < 0) {
063            throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
064        }
065
066        final int byteCodeRewriteLength = rewrite.length;
067
068        if (absPosition + 3 > byteCodeRewriteLength) {
069            throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition
070                + " but this won't fit in the rewrite array");
071        }
072
073        rewrite[absPosition] = (0xFF000000 & operand) >> 24;
074        rewrite[absPosition + 1] = (0x00FF0000 & operand) >> 16;
075        rewrite[absPosition + 2] = (0x0000FF00 & operand) >> 8;
076        rewrite[absPosition + 3] = 0x000000FF & operand;
077    }
078
079    /**
080     * Given an int operand, set the rewrite bytes for the next available operand position and the three immediately
081     * following it to a highest-byte, mid-high, mid-low, low-byte encoding of the operand.
082     *
083     * Note that unlike the ByteCode setOperand* operations, this starts with an actual bytecode rewrite array (rather
084     * than a ByteCodeForm prototype rewrite array). Also, this method overwrites -1 values in the rewrite array - so if
085     * you start with an array that looks like: {100, -1, -1, -1, -1, 200, -1, -1, -1, -1} then calling
086     * setRewrite4Bytes(0, rewrite) the first time will convert it to: {100, 0, 0, 0, 0, 200, -1, -1, -1, -1} Calling
087     * setRewrite4Bytes(0, rewrite) a second time will convert it to: {100, 0, 0, 0, 0, 200, 0, 0, 0, 0}
088     *
089     * @param operand int to set the rewrite bytes to
090     * @param rewrite int[] bytes to rewrite
091     */
092    public void setRewrite4Bytes(final int operand, final int[] rewrite) {
093        int firstOperandPosition = -1;
094
095        // Find the first -1 in the rewrite array
096        for (int index = 0; index < rewrite.length - 3; index++) {
097            if (rewrite[index] == -1 && rewrite[index + 1] == -1 && rewrite[index + 2] == -1
098                && rewrite[index + 3] == -1) {
099                firstOperandPosition = index;
100                break;
101            }
102        }
103        setRewrite4Bytes(operand, firstOperandPosition, rewrite);
104    }
105}