MultiGate.java

/* 
 * 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 kodkod.util.ints.Ints;


/**
 * A logic gate with two or more inputs; an AND or an OR gate.
 *  
 * @specfield op: Operator.Binary
 * @invariant #inputs > 1
 * @invariant some components.this => label in [1..Integer.MAX_VALUE), label in [0..Integer.MAX_VALUE)
 * @invariant no c1, c2: inputs | c1.label = -c2.label
 * @invariant this.label > 0 => all c: inputs | |c.label| < this.label
 * @author Emina Torlak
 */
public abstract class MultiGate extends BooleanFormula {
	final Operator.Nary op;
	
	private final int label, labelhash, hashcode;
	
	/**
	 * Constructs a new MultiGate gate with the given operator and label.
	 * @requires op != null && label >= 0
	 * @ensures this.op' = op && this.label' = label
	 */
	 MultiGate(Operator.Nary op, int label, int hashcode) {
		super(null);
		assert op != null;
		assert label >= 0;
		this.op = op;
		this.label = label;
		this.labelhash = Ints.superFastHash(label);
		this.hashcode = hashcode;
	}
	
	/**
	 * Returns the label for this value. 
	 * @return this.label
	 */
	@Override
	public final int label() { return label; }
	
	/**
	 * Returns the operator used to combine the input
	 * variables of this connective gate.
	 * @return this.op
	 */
	public final Operator.Nary op() { return op; }
	
	/**
	 * 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 multigate.
	 * @return a string representation of this multigate.
	 */
	public String toString() {
		final StringBuilder builder = new StringBuilder("(");
		final Iterator<BooleanFormula> children = iterator();
		builder.append(children.next());
		while(children.hasNext()) {
			builder.append(op);
			builder.append(children.next());
		}
		builder.append(")");
		return builder.toString();
	}
	
	/**
	 * Returns a hashcode for this gate.  The hashcode obeys the Object contract.
	 * @return a hashcode for this gate.
	 */
	@Override
	public final int hashCode() {
		return hashcode;
	}
	
	/**
	 * Returns the digest of this formula that would be used
	 * to compute the digest of the composition of this and
	 * some other formula using the given operator.  Specifically,
	 * if op = this.op, then the sum of this circuit's irreducible
	 * inputs' hashes (with respect to op) is returned.  Otherwise, 
	 * the superFastHash of this.label is returned.
	 * @return this.op = op => this.op.hash(this.inputs), Ints.superFastHash(this.label)
	 */
	@Override
	final int hash(Operator op) {
		return op==this.op ? hashcode : labelhash; 
	}
}