switch.java

该开源工具主要用于class文件的操作

package org.apache.bcel.generic;

/* ====================================================================
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/** 
 * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or
 * TABLESWITCH instruction, depending on whether the match values (int[]) can be
 * sorted with no gaps between the numbers.
 *
 * @version $Id: SWITCH.java,v 1.1.1.1 2001/10/29 20:00:27 jvanzyl Exp $
 * @author  <A HREF="mailto:[e-mail]">M. Dahm</A>
 */
public final class SWITCH implements CompoundInstruction {
  private int[]               match;
  private InstructionHandle[] targets;
  private Select              instruction;
  private int                 match_length;

  /**
   * Template for switch() constructs. If the match array can be
   * sorted in ascending order with gaps no larger than max_gap
   * between the numbers, a TABLESWITCH instruction is generated, and
   * a LOOKUPSWITCH otherwise. The former may be more efficient, but
   * needs more space.
   * 
   * Note, that the key array always will be sorted, though we leave
   * the original arrays unaltered.
   *
   * @param match array of match values (case 2: ... case 7: ..., etc.)
   * @param targets the instructions to be branched to for each case
   * @param target the default target
   * @param max_gap maximum gap that may between case branches
   */
  public SWITCH(int[] match, InstructionHandle[] targets,
		InstructionHandle target, int max_gap) {
    this.match   = (int[])match.clone();
    this.targets = (InstructionHandle[])targets.clone();

    if((match_length = match.length) < 2) // (almost) empty switch, or just default
      instruction = new TABLESWITCH(match, targets, target);
    else {
      sort(0, match_length - 1);
      
      if(matchIsOrdered(max_gap)) {
	fillup(max_gap, target);

	instruction = new TABLESWITCH(this.match, this.targets, target);
      }
      else
	instruction = new LOOKUPSWITCH(this.match, this.targets, target);
    }
  }

  public SWITCH(int[] match, InstructionHandle[] targets,
		InstructionHandle target) {
    this(match, targets, target, 1);
  }
  
  private final void fillup(int max_gap, InstructionHandle target) {
    int                 max_size = match_length + match_length * max_gap;
    int[]               m_vec    = new int[max_size];
    InstructionHandle[] t_vec    = new InstructionHandle[max_size];
    int                 count    = 1;

    m_vec[0] = match[0];
    t_vec[0] = targets[0];

    for(int i=1; i < match_length; i++) {
      int prev = match[i-1];
      int gap  = match[i] - prev; 

      for(int j=1; j < gap; j++) {
	m_vec[count] = prev + j;
	t_vec[count] = target;
	count++;
      }

      m_vec[count] = match[i];
      t_vec[count] = targets[i];
      count++;
    }	

    match   = new int[count];
    targets = new InstructionHandle[count];

    System.arraycopy(m_vec, 0, match, 0, count);
    System.arraycopy(t_vec, 0, targets, 0, count);
  }

  /**
   * Sort match and targets array with QuickSort.
   */
  private final void sort(int l, int r) {
    int i = l, j = r;
    int h, m = match[(l + r) / 2];
    InstructionHandle h2;

    do {
      while(match[i] < m) i++;
      while(m < match[j]) j--;

      if(i <= j) {
	h=match[i]; match[i]=match[j]; match[j]=h; // Swap elements
	h2=targets[i]; targets[i]=targets[j]; targets[j]=h2; // Swap instructions, too
	i++; j--;
      }
    } while(i <= j);

    if(l < j) sort(l, j);
    if(i < r) sort(i, r);
  }

  /**
   * @return match is sorted in ascending order with no gap bigger than max_gap?
   */
  private final boolean matchIsOrdered(int max_gap) {
    for(int i=1; i < match_length; i++)
      if(match[i] - match[i-1] > max_gap)
	return false;

    return true;
  }

  public final InstructionList getInstructionList() {
    return new InstructionList(instruction);
  }

  public final Instruction getInstruction() {
    return instruction;
  }
}