| /* |
| * 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.qual.Nullable; |
| |
| /** |
| * 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(@Nullable 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; |
| } |
| } |