content: /* 
   * Kodkod -- Copyright (c) 2005-present, Emina Torlak
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  package kodkod.engine.bool;
  
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import kodkod.util.ints.Ints;
  
  
  /**
   * A logic NOT gate.
   * 
   * @invariant this.op = Operator.NOT
   * @invariant #inputs = 1 
   * @invariant this.label = -inputs.label
   * @invariant label in (-Integer.MAX_VALUE..-1]
   * @author Emina Torlak
   */
  public final class NotGate extends BooleanFormula {
  
  	private final int hashcode;
  	
  	/**
  	 * Constructs a new NotGate with the given formula as its input.
  	 * @requires input != null && input !in NotGate
  	 * @ensures this.inputs' = 0->input && this.output'.label = -input.label
  	 */
  	NotGate(BooleanFormula input) {
  		super(input);
  		this.hashcode = Ints.superFastHash(-input.label());
  	}
  	
  	/**
  	 * Returns a hash of this inverter's label.
  	 * @return Ints.superFastHash(this.label)
  	 */
  	@Override
  	int hash(Operator op) {
  		return hashcode;
  	}
  
  	/**
  	 * Returns an iterator that returns this gate's single input.
  	 * @return an iterator over this.inputs.
  	 */
  	@Override
  	public Iterator<BooleanFormula> iterator() {
  		return new Iterator<BooleanFormula>() {
  			boolean hasNext = true;
  			public boolean hasNext() {
  				return hasNext;
  			}
  
  			public BooleanFormula next() {
  				if (!hasNext) throw new NoSuchElementException();
  				hasNext = false;
  				return negation();
  			}
  
  			public void remove() {
  				throw new UnsupportedOperationException();
  			}
  			
  		};
  	}
  	
  	/**
  	 * Returns the label for this value. 
  	 * @return this.label
  	 */
  	@Override
  	public final int label() { return -negation().label(); }
  	
  	/**
  	 * Returns 1.
  	 * @return 1.
  	 */
  	@Override
  	public int size() {
  		return 1;
  	}
  	
  	/**
  	 * Passes this value and the given
  	 * argument value to the visitor, and returns the resulting value.
  	 * @return the value produced by the visitor when visiting this node
  	 * with the given argument.
  	 */
  	@Override
  	public <T, A> T accept(BooleanVisitor<T,A> visitor, A arg) {
  		return visitor.visit(this, arg);
  	}
  	
  	/**
  	 * Returns a string representation of this inverter.
  	 * @return a string representation of this inverter.
  	 */
  	public String toString() {
  		return "!" + negation().toString();
  	}
  
  	/**
  	 * Returns Operator.NOT.
  	 * @return Operator.NOT
  	 */
  	@Override
  	public kodkod.engine.bool.Operator op() {
  		return kodkod.engine.bool.Operator.NOT;
  	}
  
  	/**
  	 * Returns this.input[i].
  	 * @return this.input[i]
  	 * @throws IndexOutOfBoundsException  i != 0
  	 */
  	@Override
  	public BooleanFormula input(int i) {
  		if (i != 0) throw new IndexOutOfBoundsException();
  		return negation();
  	}
  
  	/**
  	 * Returns a hashcode for this inverter.
  	 * @return a hashcode for this inverter.
  	 */
  	public int hashCode() { 
  		return hashcode;
  	}
  }
  