/*
* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.sun.tools.javac.util;
/**
* A hash table that maps Object to int.
*
* This is a custom hash table optimised for the Object {@literal ->} int
* maps. This is done to avoid unnecessary object allocation in the image set.
*
* @author Charles Turner
* @author Per Bothner
*/
public class IntHashTable {
private static final int DEFAULT_INITIAL_SIZE = 64;
protected Object[] objs; // the domain set
protected int[] ints; // the image set
protected int mask; // used to clip int's into the domain
protected int num_bindings; // the number of mappings (including DELETED)
private final static Object DELETED = new Object();
/**
* Construct an Object {@literal ->} int hash table.
*
* The default size of the hash table is 64 mappings.
*/
public IntHashTable() {
objs = new Object[DEFAULT_INITIAL_SIZE];
ints = new int[DEFAULT_INITIAL_SIZE];
mask = DEFAULT_INITIAL_SIZE - 1;
}
/**
* Construct an Object {@literal ->} int hash table with a specified amount of mappings.
* @param capacity The number of default mappings in this hash table.
*/
public IntHashTable(int capacity) {
int log2Size = 4;
while (capacity > (1 << log2Size)) {
log2Size++;
}
capacity = 1 << log2Size;
objs = new Object[capacity];
ints = new int[capacity];
mask = capacity - 1;
}
/**
* Compute the hash code of a given object.
*
* @param key The object whose hash code is to be computed.
* @return zero if the object is null, otherwise the identityHashCode
*/
public int hash(Object key) {
return System.identityHashCode(key);
}
/**
* Find either the index of a key's value, or the index of an available space.
*
* @param key The key to whose value you want to find.
* @param hash The hash code of this key.
* @return Either the index of the key's value, or an index pointing to
* unoccupied space.
*/
public int lookup(Object key, int hash) {
Object node;
int hash1 = hash ^ (hash >>> 15);
int hash2 = (hash ^ (hash << 6)) | 1; //ensure coprimeness
int deleted = -1;
for (int i = hash1 & mask;; i = (i + hash2) & mask) {
node = objs[i];
if (node == key)
return i;
if (node == null)
return deleted >= 0 ? deleted : i;
if (node == DELETED && deleted < 0)
deleted = i;
}
}
/**
* Lookup a given key's value in the hash table.
*
* @param key The key whose value you want to find.
* @return Either the index of the key's value, or an index pointing to
* unoccupied space.
*/
public int lookup(Object key) {
return lookup(key, hash(key));
}
/**
* Return the value stored at the specified index in the table.
*
* @param index The index to inspect, as returned from {@link #lookup}
* @return A non-negative integer if the index contains a non-null
* value, or -1 if it does.
*/
public int getFromIndex(int index) {
Object node = objs[index];
return node == null || node == DELETED ? -1 : ints[index];
}
/**
* Associates the specified key with the specified value in this map.
*
* @param key key with which the specified value is to be associated.
* @param value value to be associated with the specified key.
* @param index the index at which to place this binding, as returned
* from {@link #lookup}.
* @return previous value associated with specified key, or -1 if there was
* no mapping for key.
*/
public int putAtIndex(Object key, int value, int index) {
Object old = objs[index];
if (old == null || old == DELETED) {
objs[index] = key;
ints[index] = value;
if (old != DELETED)
num_bindings++;
if (3 * num_bindings >= 2 * objs.length)
rehash();
return -1;
} else { // update existing mapping
int oldValue = ints[index];
ints[index] = value;
return oldValue;
}
}
public int remove(Object key) {
int index = lookup(key);
Object old = objs[index];
if (old == null || old == DELETED)
return -1;
objs[index] = DELETED;
return ints[index];
}
/**
* Expand the hash table when it exceeds the load factor.
*
* Rehash the existing objects.
*/
protected void rehash() {
Object[] oldObjsTable = objs;
int[] oldIntsTable = ints;
int oldCapacity = oldObjsTable.length;
int newCapacity = oldCapacity << 1;
Object[] newObjTable = new Object[newCapacity];
int[] newIntTable = new int[newCapacity];
int newMask = newCapacity - 1;
objs = newObjTable;
ints = newIntTable;
mask = newMask;
num_bindings = 0; // this is recomputed below
Object key;
for (int i = oldIntsTable.length; --i >= 0;) {
key = oldObjsTable[i];
if (key != null && key != DELETED)
putAtIndex(key, oldIntsTable[i], lookup(key, hash(key)));
}
}
/**
* Removes all mappings from this map.
*/
public void clear() {
for (int i = objs.length; --i >= 0;) {
objs[i] = null;
}
num_bindings = 0;
}
}