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     * Given an int operand, set the rewrite bytes for the next available operand position and the three immediately
031     * following it to a highest-byte, mid-high, mid-low, low-byte encoding of the operand.
032     *
033     * Note that unlike the ByteCode setOperand* operations, this starts with an actual bytecode rewrite array (rather
034     * than a ByteCodeForm prototype rewrite array). Also, this method overwrites -1 values in the rewrite array - so if
035     * you start with an array that looks like: {100, -1, -1, -1, -1, 200, -1, -1, -1, -1} then calling
036     * setRewrite4Bytes(0, rewrite) the first time will convert it to: {100, 0, 0, 0, 0, 200, -1, -1, -1, -1} Calling
037     * setRewrite4Bytes(0, rewrite) a second time will convert it to: {100, 0, 0, 0, 0, 200, 0, 0, 0, 0}
038     *
039     * @param operand int to set the rewrite bytes to
040     * @param rewrite int[] bytes to rewrite
041     */
042    public void setRewrite4Bytes(final int operand, final int[] rewrite) {
043        int firstOperandPosition = -1;
044
045        // Find the first -1 in the rewrite array
046        for (int index = 0; index < rewrite.length - 3; index++) {
047            if ((rewrite[index] == -1) && (rewrite[index + 1] == -1) && (rewrite[index + 2] == -1)
048                && (rewrite[index + 3] == -1)) {
049                firstOperandPosition = index;
050                break;
051            }
052        }
053        setRewrite4Bytes(operand, firstOperandPosition, rewrite);
054    }
055
056    /**
057     * This method writes operand directly into the rewrite array at index position specified.
058     *
059     * @param operand value to write
060     * @param absPosition position in array to write. Note that this is absolute position in the array, so one can
061     *        overwrite the bytecode if one isn't careful.
062     * @param rewrite array to write into
063     */
064    public void setRewrite4Bytes(final int operand, final int absPosition, final int[] rewrite) {
065        if (absPosition < 0) {
066            throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
067        }
068
069        final int byteCodeRewriteLength = rewrite.length;
070
071        if (absPosition + 3 > byteCodeRewriteLength) {
072            throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition
073                + " but this won't fit in the rewrite array");
074        }
075
076        rewrite[absPosition] = ((0xFF000000) & operand) >> 24;
077        rewrite[absPosition + 1] = ((0x00FF0000) & operand) >> 16;
078        rewrite[absPosition + 2] = ((0x0000FF00) & operand) >> 8;
079        rewrite[absPosition + 3] = ((0x000000FF) & operand);
080    }
081
082    /**
083     * This method writes operand directly into the rewrite array at index position specified.
084     *
085     * @param operand value to write
086     * @param absPosition position in array to write. Note that this is absolute position in the array, so one can
087     *        overwrite the bytecode if one isn't careful.
088     * @param rewrite array to write into
089     */
090    public void setRewrite2Bytes(final int operand, final int absPosition, final int[] rewrite) {
091        if (absPosition < 0) {
092            throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
093        }
094
095        final int byteCodeRewriteLength = rewrite.length;
096
097        if (absPosition + 1 > byteCodeRewriteLength) {
098            throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition
099                + " but this won't fit in the rewrite array");
100        }
101
102        rewrite[absPosition] = ((0xFF00) & operand) >> 8;
103        rewrite[absPosition + 1] = ((0x00FF) & operand);
104    }
105}