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package org.apache.lucene.util;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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* Simple lockless and memory barrier free String intern cache that is guaranteed
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* to return the same String instance as String.intern()
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public class SimpleStringInterner extends StringInterner {
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private static class Entry {
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final private String str;
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final private int hash;
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private Entry(String str, int hash, Entry next) {
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private final Entry[] cache;
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private final int maxChainLength;
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* @param tableSize Size of the hash table, should be a power of two.
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* @param maxChainLength Maximum length of each bucket, after which the oldest item inserted is dropped.
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public SimpleStringInterner(int tableSize, int maxChainLength) {
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cache = new Entry[Math.max(1,BitUtil.nextHighestPowerOfTwo(tableSize))];
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this.maxChainLength = Math.max(2,maxChainLength);
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public String intern(String s) {
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// In the future, it may be worth augmenting the string hash
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// if the lower bits need better distribution.
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int slot = h & (cache.length-1);
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Entry first = this.cache[slot];
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Entry nextToLast = null;
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for(Entry e=first; e!=null; e=e.next) {
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if (e.hash == h && (e.str == s || e.str.compareTo(s)==0)) {
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// if (e.str == s || (e.hash == h && e.str.compareTo(s)==0)) {
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// insertion-order cache: add new entry at head
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this.cache[slot] = new Entry(s, h, first);
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if (chainLength >= maxChainLength) {
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nextToLast.next = null;
b'\\ No newline at end of file'