com.google.common.collect.Hashing Maven / Gradle / Ivy
/*
* Copyright (C) 2008 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import com.google.common.annotations.GwtCompatible;
import com.google.common.primitives.Ints;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* Static methods for implementing hash-based collections.
*
* @author Kevin Bourrillion
* @author Jesse Wilson
* @author Austin Appleby
*/
@GwtCompatible
final class Hashing {
private Hashing() {}
/*
* These should be ints, but we need to use longs to force GWT to do the multiplications with
* enough precision.
*/
private static final long C1 = 0xcc9e2d51;
private static final long C2 = 0x1b873593;
/*
* This method was rewritten in Java from an intermediate step of the Murmur hash function in
* http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which contained the
* following header:
*
* MurmurHash3 was written by Austin Appleby, and is placed in the public domain. The author
* hereby disclaims copyright to this source code.
*/
static int smear(int hashCode) {
return (int) (C2 * Integer.rotateLeft((int) (hashCode * C1), 15));
}
static int smearedHash(@NullableDecl Object o) {
return smear((o == null) ? 0 : o.hashCode());
}
private static final int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;
static int closedTableSize(int expectedEntries, double loadFactor) {
// Get the recommended table size.
// Round down to the nearest power of 2.
expectedEntries = Math.max(expectedEntries, 2);
int tableSize = Integer.highestOneBit(expectedEntries);
// Check to make sure that we will not exceed the maximum load factor.
if (expectedEntries > (int) (loadFactor * tableSize)) {
tableSize <<= 1;
return (tableSize > 0) ? tableSize : MAX_TABLE_SIZE;
}
return tableSize;
}
static boolean needsResizing(int size, int tableSize, double loadFactor) {
return size > loadFactor * tableSize && tableSize < MAX_TABLE_SIZE;
}
}