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/*
 * Copyright (c) 2002 - 2006 IBM Corporation.
 * 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
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 */
package com.ibm.wala.dataflow.graph;

import com.ibm.wala.fixpoint.BitVectorVariable;
import com.ibm.wala.fixpoint.UnaryOperator;
import org.jspecify.annotations.Nullable;

/** Operator U(n) = U(n) U U(j) */
public class UnaryBitVectorUnion extends UnaryOperator {

  private static final UnaryBitVectorUnion SINGLETON = new UnaryBitVectorUnion();

  public static UnaryBitVectorUnion instance() {
    return SINGLETON;
  }

  private UnaryBitVectorUnion() {}

  @Override
  public byte evaluate(@Nullable BitVectorVariable lhs, BitVectorVariable rhs)
      throws IllegalArgumentException {
    if (lhs == null) {
      throw new IllegalArgumentException("lhs == null");
    }

    BitVectorVariable U = new BitVectorVariable();
    U.copyState(lhs);
    U.addAll(rhs);
    if (lhs.sameValue(U)) {
      return NOT_CHANGED;
    } else {
      lhs.copyState(U);
      return CHANGED;
    }
  }

  @Override
  public String toString() {
    return "UNION";
  }

  @Override
  public int hashCode() {
    return 9901;
  }

  @Override
  public boolean equals(Object o) {
    return (o instanceof UnaryBitVectorUnion);
  }
}