/*******************************************************************************
    * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
    *
    * All rights reserved. This program and the accompanying materials
    * are made available under the terms of the Eclipse Public License v1.0
    * which accompanies this distribution, and is available at
    * http://www.eclipse.org/legal/epl-v10.html
    *
    * Alternatively, the contents of this file may be used under the terms of
   * either the GNU Lesser General Public License Version 2.1 or later (the
   * "LGPL"), in which case the provisions of the LGPL are applicable instead
   * of those above. If you wish to allow use of your version of this file only
   * under the terms of the LGPL, and not to allow others to use your version of
   * this file under the terms of the EPL, indicate your decision by deleting
   * the provisions above and replace them with the notice and other provisions
   * required by the LGPL. If you do not delete the provisions above, a recipient
   * may use your version of this file under the terms of the EPL or the LGPL.
   * 
   * Based on the original MiniSat specification from:
   * 
   * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
   * Sixth International Conference on Theory and Applications of Satisfiability
   * Testing, LNCS 2919, pp 502-518, 2003.
   *
   * See www.minisat.se for the original solver in C++.
   * 
   *******************************************************************************/
  package org.sat4j.minisat.restarts;
  
  import org.sat4j.minisat.core.RestartStrategy;
  import org.sat4j.minisat.core.SearchParams;
  
  /**
   * Luby series
   */
  public final class LubyRestarts implements RestartStrategy {
  
  	private static final int DEFAULT_LUBY_FACTOR = 32;
  	private static final int PRECOMPUTED_VALUES_IN_POOL = 32;
  	/**
       * 
       */
  	private static final long serialVersionUID = 1L;
  
  	private static int[] cachedValues = new int[] { 0, 1, 1, 2 };
  
  	public static final int luby(int i) {
  		if (i >= Integer.MAX_VALUE / 2) {
  			throw new IllegalArgumentException("i is too big");
  		}
  		if (i >= cachedValues.length) {
  			int oldsize = cachedValues.length;
  			int newsize = i << 1;
  			int[] newContent = new int[newsize + 1];
  			System.arraycopy(cachedValues, 0, newContent, 0, oldsize);
  			int nextPowerOfTwo = 1;
  			while (nextPowerOfTwo <= oldsize) {
  				nextPowerOfTwo <<= 1;
  			}
  			int lastPowerOfTwo = nextPowerOfTwo >> 1;
  			for (int j = oldsize; j <= newsize; j++) {
  				if (j + 1 == nextPowerOfTwo) {
  					newContent[j] = lastPowerOfTwo;
  					lastPowerOfTwo = nextPowerOfTwo;
  					nextPowerOfTwo <<= 1;
  				} else {
  					newContent[j] = newContent[j - lastPowerOfTwo + 1];
  				}
  			}
  			cachedValues = newContent;
  
  		}
  		return cachedValues[i];
  	}
  
  	static {
  		luby(PRECOMPUTED_VALUES_IN_POOL);
  	}
  
  	private int factor;
  
  	private int count;
  
  	public LubyRestarts() {
  		this(DEFAULT_LUBY_FACTOR); // uses TiniSAT default
  	}
  
  	/**
  	 * @param factor
  	 *            the factor used for the Luby series.
  	 * @since 2.1
  	 */
  	public LubyRestarts(int factor) {
  		setFactor(factor);
  	}
  
  	public final void setFactor(int factor) {
  		this.factor = factor;
  	}
 
 	public int getFactor() {
 		return factor;
 	}
 
 	public void init(SearchParams params) {
 		count = 1;
 	}
 
 	public long nextRestartNumberOfConflict() {
 		return luby(count) * factor;
 	}
 
 	public void onRestart() {
 		count++;
 	}
 
 	@Override
 	public String toString() {
 		return "luby style (SATZ_rand, TiniSAT) restarts strategy with factor "
 				+ factor;
 	}
 
 }