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	/*
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* ASM: a very small and fast Java bytecode manipulation framework
	* Copyright (c) 2000-2011 INRIA, France Telecom
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	* 3. Neither the name of the copyright holders nor the names of its
	* contributors may be used to endorse or promote products derived from
	* this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
	* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
	* THE POSSIBILITY OF SUCH DAMAGE.
	*/
	package jdk.internal.org.objectweb.asm.tree.analysis;

	import java.util.AbstractSet;
	import java.util.HashSet;
	import java.util.Iterator;
	import java.util.NoSuchElementException;
	import java.util.Set;

	/**
	* An immutable set of at most two elements, optimized for speed compared to a generic set
	* implementation.
	*
	* @author Eric Bruneton
	*/
	final class SmallSet<T> extends AbstractSet<T> {

	/** The first element of this set, maybe {@literal null}. */
	private final T element1;

	/**
	* The second element of this set, maybe {@literal null}. If {@link #element1} is {@literal null}
	* then this field must be {@literal null}, otherwise it must be different from {@link #element1}.
	*/
	private final T element2;

	// -----------------------------------------------------------------------------------------------
	// Constructors
	// -----------------------------------------------------------------------------------------------

	/** Constructs an empty set. */
	SmallSet() {
	this.element1 = null;
	this.element2 = null;
	}

	/**
	* Constructs a set with exactly one element.
	*
	* @param element the unique set element.
	*/
	SmallSet(final T element) {
	this.element1 = element;
	this.element2 = null;
	}

	/**
	* Constructs a new {@link SmallSet}.
	*
	* @param element1 see {@link #element1}.
	* @param element2 see {@link #element2}.
	*/
	private SmallSet(final T element1, final T element2) {
	this.element1 = element1;
	this.element2 = element2;
	}

	// -----------------------------------------------------------------------------------------------
	// Implementation of the inherited abstract methods
	// -----------------------------------------------------------------------------------------------

	@Override
	public Iterator<T> iterator() {
	return new IteratorImpl<>(element1, element2);
	}

	@Override
	public int size() {
	if (element1 == null) {
	return 0;
	} else if (element2 == null) {
	return 1;
	} else {
	return 2;
	}
	}

	// -----------------------------------------------------------------------------------------------
	// Utility methods
	// -----------------------------------------------------------------------------------------------

	/**
	* Returns the union of this set and of the given set.
	*
	* @param otherSet another small set.
	* @return the union of this set and of otherSet.
	*/
	Set<T> union(final SmallSet<T> otherSet) {
	// If the two sets are equal, return this set.
	if ((otherSet.element1 == element1 && otherSet.element2 == element2)
	\|\| (otherSet.element1 == element2 && otherSet.element2 == element1)) {
	return this;
	}
	// If one set is empty, return the other.
	if (otherSet.element1 == null) {
	return this;
	}
	if (element1 == null) {
	return otherSet;
	}

	// At this point we know that the two sets are non empty and are different.
	// If otherSet contains exactly one element:
	if (otherSet.element2 == null) {
	// If this set also contains exactly one element, we have two distinct elements.
	if (element2 == null) {
	return new SmallSet<>(element1, otherSet.element1);
	}
	// If otherSet is included in this set, return this set.
	if (otherSet.element1 == element1 \|\| otherSet.element1 == element2) {
	return this;
	}
	}
	// If this set contains exactly one element, then otherSet contains two elements (because of the
	// above tests). Thus, if otherSet contains this set, return otherSet:
	if (element2 == null && (element1 == otherSet.element1 \|\| element1 == otherSet.element2)) {
	return otherSet;
	}

	// At this point we know that there are at least 3 distinct elements, so we need a generic set
	// to store the result.
	HashSet<T> result = new HashSet<>(4);
	result.add(element1);
	if (element2 != null) {
	result.add(element2);
	}
	result.add(otherSet.element1);
	if (otherSet.element2 != null) {
	result.add(otherSet.element2);
	}
	return result;
	}

	static class IteratorImpl<T> implements Iterator<T> {

	/** The next element to return in {@link #next}. Maybe {@literal null}. */
	private T firstElement;

	/**
	* The element to return in {@link #next}, after {@link #firstElement} is returned. If {@link
	* #firstElement} is {@literal null} then this field must be {@literal null}, otherwise it must
	* be different from {@link #firstElement}.
	*/
	private T secondElement;

	IteratorImpl(final T firstElement, final T secondElement) {
	this.firstElement = firstElement;
	this.secondElement = secondElement;
	}

	@Override
	public boolean hasNext() {
	return firstElement != null;
	}

	@Override
	public T next() {
	if (firstElement == null) {
	throw new NoSuchElementException();
	}
	T element = firstElement;
	firstElement = secondElement;
	secondElement = null;
	return element;
	}

	@Override
	public void remove() {
	throw new UnsupportedOperationException();
	}
	}
	}

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