1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.compress.harmony.unpack200.bytecode.forms;
18
19 /**
20 * This abstract class implements the common code for instructions which have variable lengths. This is currently the *switch instructions and some wide (_w)
21 * instructions.
22 */
23 public abstract class VariableInstructionForm extends ByteCodeForm {
24
25 public VariableInstructionForm(final int opcode, final String name) {
26 super(opcode, name);
27 }
28
29 /**
30 * This method writes operand directly into the rewrite array at index position specified.
31 *
32 * @param operand value to write
33 * @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.
34 * @param rewrite array to write into
35 */
36 public void setRewrite2Bytes(final int operand, final int absPosition, final int[] rewrite) {
37 if (absPosition < 0) {
38 throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
39 }
40
41 final int byteCodeRewriteLength = rewrite.length;
42
43 if (absPosition + 1 > byteCodeRewriteLength) {
44 throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition + " but this won't fit in the rewrite array");
45 }
46
47 rewrite[absPosition] = (0xFF00 & operand) >> 8;
48 rewrite[absPosition + 1] = 0x00FF & operand;
49 }
50
51 /**
52 * This method writes operand directly into the rewrite array at index position specified.
53 *
54 * @param operand value to write
55 * @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.
56 * @param rewrite array to write into
57 */
58 public void setRewrite4Bytes(final int operand, final int absPosition, final int[] rewrite) {
59 if (absPosition < 0) {
60 throw new Error("Trying to rewrite " + this + " but there is no room for 4 bytes");
61 }
62
63 final int byteCodeRewriteLength = rewrite.length;
64
65 if (absPosition + 3 > byteCodeRewriteLength) {
66 throw new Error("Trying to rewrite " + this + " with an int at position " + absPosition + " but this won't fit in the rewrite array");
67 }
68
69 rewrite[absPosition] = (0xFF000000 & operand) >> 24;
70 rewrite[absPosition + 1] = (0x00FF0000 & operand) >> 16;
71 rewrite[absPosition + 2] = (0x0000FF00 & operand) >> 8;
72 rewrite[absPosition + 3] = 0x000000FF & operand;
73 }
74
75 /**
76 * 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,
77 * mid-low, low-byte encoding of the operand.
78 *
79 * Note that unlike the ByteCode setOperand* operations, this starts with an actual bytecode rewrite array (rather than a ByteCodeForm prototype rewrite
80 * 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,
81 * -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,
82 * rewrite) a second time will convert it to: {100, 0, 0, 0, 0, 200, 0, 0, 0, 0}
83 *
84 * @param operand int to set the rewrite bytes to
85 * @param rewrite int[] bytes to rewrite
86 */
87 public void setRewrite4Bytes(final int operand, final int[] rewrite) {
88 int firstOperandPosition = -1;
89
90 // Find the first -1 in the rewrite array
91 for (int index = 0; index < rewrite.length - 3; index++) {
92 if (rewrite[index] == -1 && rewrite[index + 1] == -1 && rewrite[index + 2] == -1 && rewrite[index + 3] == -1) {
93 firstOperandPosition = index;
94 break;
95 }
96 }
97 setRewrite4Bytes(operand, firstOperandPosition, rewrite);
98 }
99 }