proguard.classfile.editor.LineNumberTableAttributeTrimmer Maven / Gradle / Ivy

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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.

There is a newer version: 9.1.6

/*
 * ProGuardCORE -- library to process Java bytecode.
 *
 * Copyright (c) 2002-2020 Guardsquare NV
 *
 * Licensed 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 proguard.classfile.editor;

import java.util.Arrays;
import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;

/**
 * This {@link AttributeVisitor} trims the line number table attributes that it visits.
 *
 * @author Eric Lafortune
 */
public class LineNumberTableAttributeTrimmer implements AttributeVisitor {
  // Implementations for AttributeVisitor.

  public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

  public void visitLineNumberTableAttribute(
      Clazz clazz,
      Method method,
      CodeAttribute codeAttribute,
      LineNumberTableAttribute lineNumberTableAttribute) {
    LineNumberInfo[] lineNumberTable = lineNumberTableAttribute.lineNumberTable;
    int lineNumberTableLength = lineNumberTableAttribute.u2lineNumberTableLength;

    // Overwrite all empty line number entries.
    int newIndex = 0;
    for (int index = 0; index < lineNumberTableLength; index++) {
      LineNumberInfo lineNumberInfo = lineNumberTable[index];

      int startPC = lineNumberInfo.u2startPC;
      int lineNumber = lineNumberInfo.u2lineNumber;

      // The offset must lie inside the code.
      // The offset must be smaller than the next one.
      // The line number should be different from the previous one.
      if (startPC < codeAttribute.u4codeLength
          && (index == lineNumberTableLength - 1 || startPC < lineNumberTable[index + 1].u2startPC)
          && (index == 0 || lineNumber != lineNumberTable[index - 1].u2lineNumber)) {
        lineNumberTable[newIndex++] = lineNumberInfo;
      }
    }

    // Clear the unused array entries.
    Arrays.fill(lineNumberTable, newIndex, lineNumberTableAttribute.u2lineNumberTableLength, null);

    lineNumberTableAttribute.u2lineNumberTableLength = newIndex;
  }
}