/*
* Copyright (C) 2008 Google Inc.
*
* 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 static com.google.common.base.Preconditions.checkArgument;
/**
* Static methods for implementing hash-based collections.
*
* @author Kevin Bourrillion
* @author Jesse Wilson
*/
@GwtCompatible
final class Hashing {
private Hashing() {}
/*
* This method was written by Doug Lea with assistance from members of JCP
* JSR-166 Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
static int smear(int hashCode) {
hashCode ^= (hashCode >>> 20) ^ (hashCode >>> 12);
return hashCode ^ (hashCode >>> 7) ^ (hashCode >>> 4);
}
// We use power-of-2 tables, and this is the highest int that's a power of 2
private static final int MAX_TABLE_SIZE = 1 << 30;
// If the set has this many elements, it will "max out" the table size
private static final int CUTOFF = 1 << 29;
// Size the table to be at most 50% full, if possible
static int chooseTableSize(int setSize) {
if (setSize < CUTOFF) {
return Integer.highestOneBit(setSize) << 2;
}
// The table can't be completely full or we'll get infinite reprobes
checkArgument(setSize < MAX_TABLE_SIZE, "collection too large");
return MAX_TABLE_SIZE;
}
}