75 lines
2.3 KiB
Java
75 lines
2.3 KiB
Java
/*
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* Copyright (C) 2008 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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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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*/
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package com.google.common.collect;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.primitives.Ints;
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/**
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* Static methods for implementing hash-based collections.
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*
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* @author Kevin Bourrillion
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* @author Jesse Wilson
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* @author Austin Appleby
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*/
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@GwtCompatible
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final class Hashing {
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private Hashing() {
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}
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private static final int C1 = 0xcc9e2d51;
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private static final int C2 = 0x1b873593;
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/*
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* This method was rewritten in Java from an intermediate step of the Murmur
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* hash function in
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* http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which
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* contained the following header:
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*
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* MurmurHash3 was written by Austin Appleby, and is placed in the public
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* domain. The author hereby disclaims copyright to this source code.
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*/
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static int smear(int hashCode) {
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return C2 * Integer.rotateLeft(hashCode * C1, 15);
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}
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static int smearedHash(@Nullable Object o) {
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return smear((o == null) ? 0 : o.hashCode());
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}
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private static int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;
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static int closedTableSize(int expectedEntries, double loadFactor) {
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// Get the recommended table size.
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// Round down to the nearest power of 2.
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expectedEntries = Math.max(expectedEntries, 2);
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int tableSize = Integer.highestOneBit(expectedEntries);
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// Check to make sure that we will not exceed the maximum load factor.
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if (expectedEntries > (int) (loadFactor * tableSize)) {
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tableSize <<= 1;
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return (tableSize > 0) ? tableSize : MAX_TABLE_SIZE;
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}
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return tableSize;
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}
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static boolean needsResizing(int size, int tableSize, double loadFactor) {
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return size > loadFactor * tableSize && tableSize < MAX_TABLE_SIZE;
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}
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}
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