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Standard library for the Scala Programming Language
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala.collection
package mutable
import scala.annotation.tailrec
import scala.collection.Stepper.EfficientSplit
import scala.collection.generic.DefaultSerializationProxy
import scala.util.hashing.MurmurHash3
/** This class implements mutable sets using a hashtable.
*
* @see [[https://docs.scala-lang.org/overviews/collections/concrete-mutable-collection-classes.html#hash-tables "Scala's Collection Library overview"]]
* section on `Hash Tables` for more information.
*
* @define Coll `mutable.HashSet`
* @define coll mutable hash set
* @define mayNotTerminateInf
* @define willNotTerminateInf
*/
final class HashSet[A](initialCapacity: Int, loadFactor: Double)
extends AbstractSet[A]
with SetOps[A, HashSet, HashSet[A]]
with StrictOptimizedIterableOps[A, HashSet, HashSet[A]]
with IterableFactoryDefaults[A, HashSet]
with Serializable {
def this() = this(HashSet.defaultInitialCapacity, HashSet.defaultLoadFactor)
import HashSet.Node
/* The Hashset class holds the following invariant:
* - For each i between 0 and table.length, the bucket at table(i) only contains elements whose hash-index is i.
* - Every bucket is sorted in ascendent hash order
* - The sum of the lengths of all buckets is equal to contentSize.
*/
/** The actual hash table. */
private[this] var table = new Array[Node[A]](tableSizeFor(initialCapacity))
/** The next size value at which to resize (capacity * load factor). */
private[this] var threshold: Int = newThreshold(table.length)
private[this] var contentSize = 0
override def size: Int = contentSize
/** Performs the inverse operation of improveHash. In this case, it happens to be identical to improveHash*/
@`inline` private[collection] def unimproveHash(improvedHash: Int): Int = improveHash(improvedHash)
/** Computes the improved hash of an original (`any.##`) hash. */
private[this] def improveHash(originalHash: Int): Int = {
// Improve the hash by xoring the high 16 bits into the low 16 bits just in case entropy is skewed towards the
// high-value bits. We only use the lowest bits to determine the hash bucket. This is the same improvement
// algorithm as in java.util.HashMap.
originalHash ^ (originalHash >>> 16)
}
/** Computes the improved hash of this element */
@`inline` private[this] def computeHash(o: A): Int = improveHash(o.##)
@`inline` private[this] def index(hash: Int) = hash & (table.length - 1)
override def contains(elem: A): Boolean = findNode(elem) ne null
@`inline` private[this] def findNode(elem: A): Node[A] = {
val hash = computeHash(elem)
table(index(hash)) match {
case null => null
case nd => nd.findNode(elem, hash)
}
}
override def sizeHint(size: Int): Unit = {
val target = tableSizeFor(((size + 1).toDouble / loadFactor).toInt)
if(target > table.length) growTable(target)
}
override def add(elem: A) : Boolean = {
if(contentSize + 1 >= threshold) growTable(table.length * 2)
addElem(elem, computeHash(elem))
}
override def addAll(xs: IterableOnce[A]): this.type = {
sizeHint(xs.knownSize)
xs match {
case hm: immutable.HashSet[A] =>
hm.foreachWithHash((k, h) => addElem(k, improveHash(h)))
this
case hm: mutable.HashSet[A] =>
val iter = hm.nodeIterator
while (iter.hasNext) {
val next = iter.next()
addElem(next.key, next.hash)
}
this
case _ => super.addAll(xs)
}
}
override def subtractAll(xs: IterableOnce[A]): this.type = {
if (size == 0) {
return this
}
xs match {
case hs: immutable.HashSet[A] =>
hs.foreachWithHashWhile { (k, h) =>
remove(k, improveHash(h))
size > 0
}
this
case hs: mutable.HashSet[A] =>
val iter = hs.nodeIterator
while (iter.hasNext) {
val next = iter.next()
remove(next.key, next.hash)
if (size == 0) return this
}
this
case _ => super.subtractAll(xs)
}
}
/** Adds an element to this set
* @param elem element to add
* @param hash the **improved** hash of `elem` (see computeHash)
*/
private[this] def addElem(elem: A, hash: Int) : Boolean = {
val idx = index(hash)
table(idx) match {
case null =>
table(idx) = new Node(elem, hash, null)
case old =>
var prev: Node[A] = null
var n = old
while((n ne null) && n.hash <= hash) {
if(n.hash == hash && elem == n.key) return false
prev = n
n = n.next
}
if(prev eq null)
table(idx) = new Node(elem, hash, old)
else
prev.next = new Node(elem, hash, prev.next)
}
contentSize += 1
true
}
private[this] def remove(elem: A, hash: Int): Boolean = {
val idx = index(hash)
table(idx) match {
case null => false
case nd if nd.hash == hash && nd.key == elem =>
// first element matches
table(idx) = nd.next
contentSize -= 1
true
case nd =>
// find an element that matches
var prev = nd
var next = nd.next
while((next ne null) && next.hash <= hash) {
if(next.hash == hash && next.key == elem) {
prev.next = next.next
contentSize -= 1
return true
}
prev = next
next = next.next
}
false
}
}
override def remove(elem: A) : Boolean = remove(elem, computeHash(elem))
private[this] abstract class HashSetIterator[B] extends AbstractIterator[B] {
private[this] var i = 0
private[this] var node: Node[A] = null
private[this] val len = table.length
protected[this] def extract(nd: Node[A]): B
def hasNext: Boolean = {
if(node ne null) true
else {
while(i < len) {
val n = table(i)
i += 1
if(n ne null) { node = n; return true }
}
false
}
}
def next(): B =
if(!hasNext) Iterator.empty.next()
else {
val r = extract(node)
node = node.next
r
}
}
override def iterator: Iterator[A] = new HashSetIterator[A] {
override protected[this] def extract(nd: Node[A]): A = nd.key
}
/** Returns an iterator over the nodes stored in this HashSet */
private[collection] def nodeIterator: Iterator[Node[A]] = new HashSetIterator[Node[A]] {
override protected[this] def extract(nd: Node[A]): Node[A] = nd
}
override def stepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S with EfficientSplit = {
import convert.impl._
val s = shape.shape match {
case StepperShape.IntShape => new IntTableStepper[Node[A]] (size, table, _.next, _.key.asInstanceOf[Int], 0, table.length)
case StepperShape.LongShape => new LongTableStepper[Node[A]] (size, table, _.next, _.key.asInstanceOf[Long], 0, table.length)
case StepperShape.DoubleShape => new DoubleTableStepper[Node[A]](size, table, _.next, _.key.asInstanceOf[Double], 0, table.length)
case _ => shape.parUnbox(new AnyTableStepper[A, Node[A]](size, table, _.next, _.key, 0, table.length))
}
s.asInstanceOf[S with EfficientSplit]
}
private[this] def growTable(newlen: Int) = {
var oldlen = table.length
threshold = newThreshold(newlen)
if(size == 0) table = new Array(newlen)
else {
table = java.util.Arrays.copyOf(table, newlen)
val preLow: Node[A] = new Node(null.asInstanceOf[A], 0, null)
val preHigh: Node[A] = new Node(null.asInstanceOf[A], 0, null)
// Split buckets until the new length has been reached. This could be done more
// efficiently when growing an already filled table to more than double the size.
while(oldlen < newlen) {
var i = 0
while (i < oldlen) {
val old = table(i)
if(old ne null) {
preLow.next = null
preHigh.next = null
var lastLow: Node[A] = preLow
var lastHigh: Node[A] = preHigh
var n = old
while(n ne null) {
val next = n.next
if((n.hash & oldlen) == 0) { // keep low
lastLow.next = n
lastLow = n
} else { // move to high
lastHigh.next = n
lastHigh = n
}
n = next
}
lastLow.next = null
if(old ne preLow.next) table(i) = preLow.next
if(preHigh.next ne null) {
table(i + oldlen) = preHigh.next
lastHigh.next = null
}
}
i += 1
}
oldlen *= 2
}
}
}
override def filterInPlace(p: A => Boolean): this.type = {
if (nonEmpty) {
var bucket = 0
while (bucket < table.length) {
var head = table(bucket)
while ((head ne null) && !p(head.key)) {
head = head.next
contentSize -= 1
}
if (head ne null) {
var prev = head
var next = head.next
while (next ne null) {
if (p(next.key)) {
prev = next
} else {
prev.next = next.next
contentSize -= 1
}
next = next.next
}
}
table(bucket) = head
bucket += 1
}
}
this
}
/*
private[mutable] def checkTable(): Unit = {
var i = 0
var count = 0
var prev: Node[A] = null
while(i < table.length) {
var n = table(i)
prev = null
while(n != null) {
count += 1
assert(index(n.hash) == i)
if(prev ne null) assert(prev.hash <= n.hash)
prev = n
n = n.next
}
i += 1
}
assert(contentSize == count)
}
*/
private[this] def tableSizeFor(capacity: Int) =
(Integer.highestOneBit((capacity-1).max(4))*2).min(1 << 30)
private[this] def newThreshold(size: Int) = (size.toDouble * loadFactor).toInt
def clear(): Unit = {
java.util.Arrays.fill(table.asInstanceOf[Array[AnyRef]], null)
contentSize = 0
}
override def iterableFactory: IterableFactory[HashSet] = HashSet
@`inline` def addOne(elem: A): this.type = { add(elem); this }
@`inline` def subtractOne(elem: A): this.type = { remove(elem); this }
override def knownSize: Int = size
override def isEmpty: Boolean = size == 0
override def foreach[U](f: A => U): Unit = {
val len = table.length
var i = 0
while(i < len) {
val n = table(i)
if(n ne null) n.foreach(f)
i += 1
}
}
protected[this] def writeReplace(): AnyRef = new DefaultSerializationProxy(new HashSet.DeserializationFactory[A](table.length, loadFactor), this)
override protected[this] def className = "HashSet"
override def hashCode: Int = {
val setIterator = this.iterator
val hashIterator: Iterator[Any] =
if (setIterator.isEmpty) setIterator
else new HashSetIterator[Any] {
var hash: Int = 0
override def hashCode: Int = hash
override protected[this] def extract(nd: Node[A]): Any = {
hash = unimproveHash(nd.hash)
this
}
}
MurmurHash3.unorderedHash(hashIterator, MurmurHash3.setSeed)
}
}
/**
* $factoryInfo
* @define Coll `mutable.HashSet`
* @define coll mutable hash set
*/
@SerialVersionUID(3L)
object HashSet extends IterableFactory[HashSet] {
def from[B](it: scala.collection.IterableOnce[B]): HashSet[B] = {
val k = it.knownSize
val cap = if(k > 0) ((k + 1).toDouble / defaultLoadFactor).toInt else defaultInitialCapacity
new HashSet[B](cap, defaultLoadFactor) ++= it
}
def empty[A]: HashSet[A] = new HashSet[A]
def newBuilder[A]: Builder[A, HashSet[A]] = newBuilder(defaultInitialCapacity, defaultLoadFactor)
def newBuilder[A](initialCapacity: Int, loadFactor: Double): Builder[A, HashSet[A]] =
new GrowableBuilder[A, HashSet[A]](new HashSet[A](initialCapacity, loadFactor)) {
override def sizeHint(size: Int) = elems.sizeHint(size)
}
/** The default load factor for the hash table */
final def defaultLoadFactor: Double = 0.75
/** The default initial capacity for the hash table */
final def defaultInitialCapacity: Int = 16
@SerialVersionUID(3L)
private final class DeserializationFactory[A](val tableLength: Int, val loadFactor: Double) extends Factory[A, HashSet[A]] with Serializable {
def fromSpecific(it: IterableOnce[A]): HashSet[A] = new HashSet[A](tableLength, loadFactor) ++= it
def newBuilder: Builder[A, HashSet[A]] = HashSet.newBuilder(tableLength, loadFactor)
}
private[collection] final class Node[K](_key: K, _hash: Int, private[this] var _next: Node[K]) {
def key: K = _key
def hash: Int = _hash
def next: Node[K] = _next
def next_= (n: Node[K]): Unit = _next = n
@tailrec
def findNode(k: K, h: Int): Node[K] =
if(h == _hash && k == _key) this
else if((_next eq null) || (_hash > h)) null
else _next.findNode(k, h)
@tailrec
def foreach[U](f: K => U): Unit = {
f(_key)
if(_next ne null) _next.foreach(f)
}
override def toString = s"Node($key, $hash) -> $next"
}
}