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/*
* Copyright (C) 2019 The Android Open Source Project
*
* 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 android.util;
import com.android.internal.util.ArrayUtils;
import com.android.internal.util.GrowingArrayUtils;
import libcore.util.EmptyArray;
import java.util.NoSuchElementException;
/**
* A lightweight implementation for a queue with long values.
* Additionally supports getting an element with a specified position from the head of the queue.
* The queue grows in size if needed to accommodate new elements.
*
* @hide
*/
public class LongArrayQueue {
private long[] mValues;
private int mSize;
private int mHead;
private int mTail;
/**
* Initializes a queue with the given starting capacity.
*
* @param initialCapacity the capacity.
*/
public LongArrayQueue(int initialCapacity) {
if (initialCapacity == 0) {
mValues = EmptyArray.LONG;
} else {
mValues = ArrayUtils.newUnpaddedLongArray(initialCapacity);
}
mSize = 0;
mHead = mTail = 0;
}
/**
* Initializes a queue with default starting capacity.
*/
public LongArrayQueue() {
this(16);
}
private void grow() {
if (mSize < mValues.length) {
throw new IllegalStateException("Queue not full yet!");
}
final int newSize = GrowingArrayUtils.growSize(mSize);
final long[] newArray = ArrayUtils.newUnpaddedLongArray(newSize);
final int r = mValues.length - mHead; // Number of elements on and to the right of head.
System.arraycopy(mValues, mHead, newArray, 0, r);
System.arraycopy(mValues, 0, newArray, r, mHead);
mValues = newArray;
mHead = 0;
mTail = mSize;
}
/**
* Returns the number of elements in the queue.
*/
public int size() {
return mSize;
}
/**
* Removes all elements from this queue.
*/
public void clear() {
mSize = 0;
mHead = mTail = 0;
}
/**
* Adds a value to the tail of the queue.
*
* @param value the value to be added.
*/
public void addLast(long value) {
if (mSize == mValues.length) {
grow();
}
mValues[mTail] = value;
mTail = (mTail + 1) % mValues.length;
mSize++;
}
/**
* Removes an element from the head of the queue.
*
* @return the element at the head of the queue.
* @throws NoSuchElementException if the queue is empty.
*/
public long removeFirst() {
if (mSize == 0) {
throw new NoSuchElementException("Queue is empty!");
}
final long ret = mValues[mHead];
mHead = (mHead + 1) % mValues.length;
mSize--;
return ret;
}
/**
* Returns the element at the given position from the head of the queue, where 0 represents the
* head of the queue.
*
* @param position the position from the head of the queue.
* @return the element found at the given position.
* @throws IndexOutOfBoundsException if {@code position} < {@code 0} or
* {@code position} >= {@link #size()}
*/
public long get(int position) {
if (position < 0 || position >= mSize) {
throw new IndexOutOfBoundsException("Index " + position
+ " not valid for a queue of size " + mSize);
}
final int index = (mHead + position) % mValues.length;
return mValues[index];
}
/**
* Returns the element at the head of the queue, without removing it.
*
* @return the element at the head of the queue.
* @throws NoSuchElementException if the queue is empty
*/
public long peekFirst() {
if (mSize == 0) {
throw new NoSuchElementException("Queue is empty!");
}
return mValues[mHead];
}
/**
* Returns the element at the tail of the queue.
*
* @return the element at the tail of the queue.
* @throws NoSuchElementException if the queue is empty.
*/
public long peekLast() {
if (mSize == 0) {
throw new NoSuchElementException("Queue is empty!");
}
final int index = (mTail == 0) ? mValues.length - 1 : mTail - 1;
return mValues[index];
}
}
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