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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.instruction;

import java.util.Objects;
import proguard.classfile.*;
import proguard.classfile.attribute.CodeAttribute;
import proguard.classfile.instruction.visitor.InstructionVisitor;

/**
 * This interface describes an instruction that branches to a given offset in the code.
 *
 * @author Eric Lafortune
 */
public class BranchInstruction extends Instruction {
  public int branchOffset;

  /** Creates an uninitialized BranchInstruction. */
  public BranchInstruction() {}

  /**
   * Creates a BranchInstruction with the given branch offset. The branch offset is relative to this
   * instruction's offset.
   */
  public BranchInstruction(byte opcode, int branchOffset) {
    this.opcode = opcode;
    this.branchOffset = branchOffset;
  }

  /**
   * Copies the given instruction into this instruction.
   *
   * @param branchInstruction the instruction to be copied.
   * @return this instruction.
   */
  public BranchInstruction copy(BranchInstruction branchInstruction) {
    this.opcode = branchInstruction.opcode;
    this.branchOffset = branchInstruction.branchOffset;

    return this;
  }

  // Implementations for Instruction.

  public byte canonicalOpcode() {
    // Remove the _w extension, if any.
    switch (opcode) {
      case Instruction.OP_GOTO_W:
        return Instruction.OP_GOTO;

      case Instruction.OP_JSR_W:
        return Instruction.OP_JSR;

      default:
        return opcode;
    }
  }

  public Instruction shrink() {
    // Do we need an ordinary branch or a wide branch?
    if (requiredBranchOffsetSize() == 2) {
      // Can we replace the wide branch by an ordinary branch?
      if (opcode == Instruction.OP_GOTO_W) {
        opcode = Instruction.OP_GOTO;
      } else if (opcode == Instruction.OP_JSR_W) {
        opcode = Instruction.OP_JSR;
      }
    } else {
      // Can we provide a wide branch?
      if (opcode == Instruction.OP_GOTO || opcode == Instruction.OP_GOTO_W) {
        opcode = Instruction.OP_GOTO_W;
      } else if (opcode == Instruction.OP_JSR) {
        opcode = Instruction.OP_JSR_W;
      } else {
        throw new IllegalArgumentException(
            "Branch instruction can't be widened (" + this.toString() + ")");
      }
    }

    return this;
  }

  protected void readInfo(byte[] code, int offset) {
    branchOffset = readSignedValue(code, offset, branchOffsetSize());
  }

  protected void writeInfo(byte[] code, int offset) {
    if (requiredBranchOffsetSize() > branchOffsetSize()) {
      throw new IllegalArgumentException(
          "Instruction has invalid branch offset size (" + this.toString(offset) + ")");
    }

    writeSignedValue(code, offset, branchOffset, branchOffsetSize());
  }

  public int length(int offset) {
    return 1 + branchOffsetSize();
  }

  public void accept(
      Clazz clazz,
      Method method,
      CodeAttribute codeAttribute,
      int offset,
      InstructionVisitor instructionVisitor) {
    instructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, this);
  }

  public String toString(int offset) {
    return "[" + offset + "] " + toString() + " (target=" + (offset + branchOffset) + ")";
  }

  // Implementations for Object.

  @Override
  public String toString() {
    return getName() + " " + (branchOffset >= 0 ? "+" : "") + branchOffset;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    BranchInstruction that = (BranchInstruction) o;
    return opcode == that.opcode && branchOffset == that.branchOffset;
  }

  @Override
  public int hashCode() {
    return Objects.hash(opcode, branchOffset);
  }

  // Small utility methods.

  /** Returns the branch offset size for this instruction. */
  private int branchOffsetSize() {
    return opcode == Instruction.OP_GOTO_W || opcode == Instruction.OP_JSR_W ? 4 : 2;
  }

  /** Computes the required branch offset size for this instruction's branch offset. */
  private int requiredBranchOffsetSize() {
    return (short) branchOffset == branchOffset ? 2 : 4;
  }
}