code: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements. See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership. The ASF licenses this file
   * to you 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.
   */
  /*
   * $Id$
   */
  
  package org.apache.xalan.xsltc.compiler.util;
  
  import org.apache.bcel.generic.LocalVariableGen;
  import org.apache.bcel.generic.Type;
  
  /**
   * @author Jacek Ambroziak
   */
  final class SlotAllocator {
  
      private int   _firstAvailableSlot;
      private int   _size = 8;
      private int   _free = 0;
      private int[] _slotsTaken = new int[_size];
      
      public void initialize(LocalVariableGen[] vars) {
  	final int length = vars.length;
  	int slot = 0, size, index;
  
  	for (int i = 0; i < length; i++) {
  	    size  = vars[i].getType().getSize();
  	    index = vars[i].getIndex();
  	    slot  = Math.max(slot, index + size);
  	}
  	_firstAvailableSlot = slot;
      }
  
      public int allocateSlot(Type type) {
  	final int size = type.getSize();
  	final int limit = _free;
  	int slot = _firstAvailableSlot, where = 0;
  
  	if (_free + size > _size) {
  	    final int[] array = new int[_size *= 2];
  	    for (int j = 0; j < limit; j++)
  		array[j] = _slotsTaken[j];
  	    _slotsTaken = array;
  	}
  
  	while (where < limit) {
  	    if (slot + size <= _slotsTaken[where]) {
  		// insert
  		for (int j = limit - 1; j >= where; j--)
  		    _slotsTaken[j + size] = _slotsTaken[j];
  		break;
  	    }
  	    else {
  		slot = _slotsTaken[where++] + 1;
  	    }
  	}
  	
  	for (int j = 0; j < size; j++)
  	    _slotsTaken[where + j] = slot + j;
  	
  	_free += size;
  	return slot;
      }
  
      public void releaseSlot(LocalVariableGen lvg) {
  	final int size = lvg.getType().getSize();
  	final int slot = lvg.getIndex();
  	final int limit = _free;
  	
  	for (int i = 0; i < limit; i++) {
  	    if (_slotsTaken[i] == slot) {
  		int j = i + size;
  		while (j < limit) {
  		    _slotsTaken[i++] = _slotsTaken[j++];
  		}
  		_free -= size;
  		return;
  	    }
  	}
  	String state = "Variable slot allocation error"+
  	               "(size="+size+", slot="+slot+", limit="+limit+")";
  	ErrorMsg err = new ErrorMsg(ErrorMsg.INTERNAL_ERR, state);
  	throw new Error(err.toString());
      }
  }
  