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package com.sun.org.apache.bcel.internal.generic;

import java.io.*;
import com.sun.org.apache.bcel.internal.util.ByteSequence;


Select - Abstract super class for LOOKUPSWITCH and TABLESWITCH instructions.

Author: M. Dahm
See Also:
/**
 * Select - Abstract super class for LOOKUPSWITCH and TABLESWITCH instructions.
 *
 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
 * @see LOOKUPSWITCH
 * @see TABLESWITCH
 * @see InstructionList
 */
public abstract class Select extends BranchInstruction
  implements VariableLengthInstruction, StackProducer
{
  protected int[]               match;        // matches, i.e., case 1: ...
  protected int[]               indices;      // target offsets
  protected InstructionHandle[] targets;      // target objects in instruction list
  protected int                 fixed_length; // fixed length defined by subclasses
  protected int                 match_length; // number of cases
  protected int                 padding = 0;  // number of pad bytes for alignment

  
Empty constructor needed for the Class.newInstance() statement in
Instruction.readInstruction(). Not to be used otherwise.

/**
   * Empty constructor needed for the Class.newInstance() statement in
   * Instruction.readInstruction(). Not to be used otherwise.
   */
  Select() {}

  
(Match, target) pairs for switch.
`Match' and `targets' must have the same length of course.

Params:
  • match – array of matching values
  • targets – instruction targets
  • target – default instruction target
/**
   * (Match, target) pairs for switch.
   * `Match' and `targets' must have the same length of course.
   *
   * @param match array of matching values
   * @param targets instruction targets
   * @param target default instruction target
   */
  Select(short opcode, int[] match, InstructionHandle[] targets,
         InstructionHandle target) {
    super(opcode, target);

    this.targets = targets;
    for(int i=0; i < targets.length; i++) {
      BranchInstruction.notifyTargetChanged(targets[i], this);
    }

    this.match = match;

    if((match_length = match.length) != targets.length)
      throw new ClassGenException("Match and target array have not the same length");

    indices = new int[match_length];
  }

  
Since this is a variable length instruction, it may shift the following
instructions which then need to update their position.
Called by InstructionList.setPositions when setting the position for every
instruction. In the presence of variable length instructions `setPositions'
performs multiple passes over the instruction list to calculate the
correct (byte) positions and offsets by calling this function.

Params:
  • offset – additional offset caused by preceding (variable length) instructions
  • max_offset – the maximum offset that may be caused by these instructions
Returns:additional offset caused by possible change of this instruction's length
/**
   * Since this is a variable length instruction, it may shift the following
   * instructions which then need to update their position.
   *
   * Called by InstructionList.setPositions when setting the position for every
   * instruction. In the presence of variable length instructions `setPositions'
   * performs multiple passes over the instruction list to calculate the
   * correct (byte) positions and offsets by calling this function.
   *
   * @param offset additional offset caused by preceding (variable length) instructions
   * @param max_offset the maximum offset that may be caused by these instructions
   * @return additional offset caused by possible change of this instruction's length
   */
  @Override
  protected int updatePosition(int offset, int max_offset) {
    position += offset; // Additional offset caused by preceding SWITCHs, GOTOs, etc.

    short old_length = length;

    /* Alignment on 4-byte-boundary, + 1, because of tag byte.
     */
    padding = (4 - ((position + 1) % 4)) % 4;
    length  = (short)(fixed_length + padding); // Update length

    return length - old_length;
  }

  
Dump instruction as byte code to stream out.

Params:
  • out – Output stream
/**
   * Dump instruction as byte code to stream out.
   * @param out Output stream
   */
  @Override
  public void dump(DataOutputStream out) throws IOException {
    out.writeByte(opcode);

    for(int i=0; i < padding; i++) // Padding bytes
      out.writeByte(0);

    index = getTargetOffset();     // Write default target offset
    out.writeInt(index);
  }

  
Read needed data (e.g. index) from file.

/**
   * Read needed data (e.g. index) from file.
   */
  @Override
  protected void initFromFile(ByteSequence bytes, boolean wide) throws IOException
  {
    padding = (4 - (bytes.getIndex() % 4)) % 4; // Compute number of pad bytes

    for(int i=0; i < padding; i++) {
      bytes.readByte();
    }

    // Default branch target common for both cases (TABLESWITCH, LOOKUPSWITCH)
    index = bytes.readInt();
  }

  
Returns:mnemonic for instruction
/**
   * @return mnemonic for instruction
   */
  @Override
  public String toString(boolean verbose) {
    final StringBuilder buf = new StringBuilder(super.toString(verbose));

    if(verbose) {
      for(int i=0; i < match_length; i++) {
        String s = "null";

        if(targets[i] != null)
          s = targets[i].getInstruction().toString();

          buf.append("(").append(match[i]).append(", ")
             .append(s).append(" = {").append(indices[i]).append("})");
      }
    }
    else
      buf.append(" ...");

    return buf.toString();
  }

  
Set branch target for `i'th case

/**
   * Set branch target for `i'th case
   */
  public final void setTarget(int i, InstructionHandle target) {
    notifyTargetChanging(targets[i], this);
    targets[i] = target;
    notifyTargetChanged(targets[i], this);
  }

  
Params:
  • old_ih – old target
  • new_ih – new target
/**
   * @param old_ih old target
   * @param new_ih new target
   */
  @Override
  public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
    boolean targeted = false;

    if(target == old_ih) {
      targeted = true;
      setTarget(new_ih);
    }

    for(int i=0; i < targets.length; i++) {
      if(targets[i] == old_ih) {
        targeted = true;
        setTarget(i, new_ih);
      }
    }

    if(!targeted)
      throw new ClassGenException("Not targeting " + old_ih);
  }

  
Returns:true, if ih is target of this instruction
/**
   * @return true, if ih is target of this instruction
   */
  @Override
  public boolean containsTarget(InstructionHandle ih) {
    if(target == ih)
      return true;

    for(int i=0; i < targets.length; i++)
      if(targets[i] == ih)
        return true;

    return false;
  }

  
Inform targets that they're not targeted anymore.

/**
   * Inform targets that they're not targeted anymore.
   */
  @Override
  void dispose() {
    super.dispose();

    for(int i=0; i < targets.length; i++)
      targets[i].removeTargeter(this);
  }

  
Returns:array of match indices
/**
   * @return array of match indices
   */
  public int[] getMatchs() { return match; }

  
Returns:array of match target offsets
/**
   * @return array of match target offsets
   */
  public int[] getIndices() { return indices; }

  
Returns:array of match targets
/**
   * @return array of match targets
   */
  public InstructionHandle[] getTargets() { return targets; }
}