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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.
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package org.aspectj.apache.bcel.generic;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact [email protected].
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache BCEL", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * .
 */

/**
 * 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: SwitchBuilder.java,v 1.2 2008/05/28 23:52:57 aclement Exp $
 * @author  M. Dahm
 */
public final class SwitchBuilder {
  private int[]               match;
  private InstructionHandle[] targets;
  private InstructionSelect              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 SwitchBuilder(int[] match, InstructionHandle[] targets,InstructionHandle target, int max_gap) {
    this.match   = match.clone();
    this.targets = targets.clone();

    if((match_length = match.length) < 2) // (almost) empty switch, or just default
      if (match.length==0) {
    	  instruction = new LOOKUPSWITCH(match,targets,target);
      } else {
    	  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 SwitchBuilder(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++) {
      int diff = (match[i]-match[i-1]);
      if(diff > max_gap || diff<0) return false;
    }
    return true;
  }

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