001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   https://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.commons.compress.harmony.unpack200.bytecode.forms;
020
021/**
022 * This abstract class implements the common code for instructions which have variable lengths. This is currently the *switch instructions and some wide (_w)
023 * instructions.
024 */
025public abstract class VariableInstructionForm extends ByteCodeForm {
026
027    /**
028     * Constructs a new instance with the specified opcode, name, operandType and rewrite.
029     *
030     * @param opcode  index corresponding to the opcode's value.
031     * @param name    String printable name of the opcode.
032     */
033    public VariableInstructionForm(final int opcode, final String name) {
034        super(opcode, name);
035    }
036
037    /**
038     * This method writes operand directly into the rewrite array at index position specified.
039     *
040     * @param operand     value to write
041     * @param absPosition position in array to write. Note that this is absolute position in the array, so one can overwrite the bytecode if one isn't careful.
042     * @param rewrite     array to write into
043     */
044    public void setRewrite2Bytes(final int operand, final int absPosition, final int[] rewrite) {
045        if (absPosition < 0) {
046            throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
047        }
048
049        final int byteCodeRewriteLength = rewrite.length;
050
051        if (absPosition + 1 > byteCodeRewriteLength) {
052            throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition + " but this won't fit in the rewrite array");
053        }
054
055        rewrite[absPosition] = (0xFF00 & operand) >> 8;
056        rewrite[absPosition + 1] = 0x00FF & operand;
057    }
058
059    /**
060     * This method writes operand directly into the rewrite array at index position specified.
061     *
062     * @param operand     value to write
063     * @param absPosition position in array to write. Note that this is absolute position in the array, so one can overwrite the bytecode if one isn't careful.
064     * @param rewrite     array to write into
065     */
066    public void setRewrite4Bytes(final int operand, final int absPosition, final int[] rewrite) {
067        if (absPosition < 0) {
068            throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
069        }
070
071        final int byteCodeRewriteLength = rewrite.length;
072
073        if (absPosition + 3 > byteCodeRewriteLength) {
074            throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition + " but this won't fit in the rewrite array");
075        }
076
077        rewrite[absPosition] = (0xFF000000 & operand) >> 24;
078        rewrite[absPosition + 1] = (0x00FF0000 & operand) >> 16;
079        rewrite[absPosition + 2] = (0x0000FF00 & operand) >> 8;
080        rewrite[absPosition + 3] = 0x000000FF & operand;
081    }
082
083    /**
084     * Given an int operand, set the rewrite bytes for the next available operand position and the three immediately following it to a highest-byte, mid-high,
085     * mid-low, low-byte encoding of the operand.
086     *
087     * Note that unlike the ByteCode setOperand* operations, this starts with an actual bytecode rewrite array (rather than a ByteCodeForm prototype rewrite
088     * array). Also, this method overwrites -1 values in the rewrite array - so if you start with an array that looks like: {100, -1, -1, -1, -1, 200, -1, -1,
089     * -1, -1} then calling setRewrite4Bytes(0, rewrite) the first time will convert it to: {100, 0, 0, 0, 0, 200, -1, -1, -1, -1} Calling setRewrite4Bytes(0,
090     * rewrite) a second time will convert it to: {100, 0, 0, 0, 0, 200, 0, 0, 0, 0}
091     *
092     * @param operand int to set the rewrite bytes to
093     * @param rewrite int[] bytes to rewrite
094     */
095    public void setRewrite4Bytes(final int operand, final int[] rewrite) {
096        int firstOperandPosition = -1;
097
098        // Find the first -1 in the rewrite array
099        for (int index = 0; index < rewrite.length - 3; index++) {
100            if (rewrite[index] == -1 && rewrite[index + 1] == -1 && rewrite[index + 2] == -1 && rewrite[index + 3] == -1) {
101                firstOperandPosition = index;
102                break;
103            }
104        }
105        setRewrite4Bytes(operand, firstOperandPosition, rewrite);
106    }
107}