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AbstractSpinedBuffer.java
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127 lines (111 loc) · 2.85 KB
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/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util.stream;
/**
* Base class for a data structure for gathering elements into a buffer and then
* iterating them. Maintains an array of increasingly sized arrays, so there is
* no copying cost associated with growing the data structure.
* @since 1.8
*/
abstract class AbstractSpinedBuffer {
/**
* Minimum power-of-two for the first chunk.
*/
public static final int MIN_CHUNK_POWER = 4;
/**
* Minimum size for the first chunk.
*/
public static final int MIN_CHUNK_SIZE = 1 << MIN_CHUNK_POWER;
/**
* Max power-of-two for chunks.
*/
public static final int MAX_CHUNK_POWER = 30;
/**
* Minimum array size for array-of-chunks.
*/
public static final int MIN_SPINE_SIZE = 8;
/**
* log2 of the size of the first chunk.
*/
protected final int initialChunkPower;
/**
* Index of the *next* element to write; may point into, or just outside of,
* the current chunk.
*/
protected int elementIndex;
/**
* Index of the *current* chunk in the spine array, if the spine array is
* non-null.
*/
protected int spineIndex;
/**
* Count of elements in all prior chunks.
*/
protected long[] priorElementCount;
/**
* Construct with an initial capacity of 16.
*/
protected AbstractSpinedBuffer() {
this.initialChunkPower = MIN_CHUNK_POWER;
}
/**
* Construct with a specified initial capacity.
*
* @param initialCapacity The minimum expected number of elements
*/
protected AbstractSpinedBuffer(int initialCapacity) {
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity);
this.initialChunkPower = Math.max(MIN_CHUNK_POWER,
Integer.SIZE - Integer.numberOfLeadingZeros(initialCapacity - 1));
}
/**
* Is the buffer currently empty?
*/
public boolean isEmpty() {
return (spineIndex == 0) && (elementIndex == 0);
}
/**
* How many elements are currently in the buffer?
*/
public long count() {
return (spineIndex == 0)
? elementIndex
: priorElementCount[spineIndex] + elementIndex;
}
/**
* How big should the nth chunk be?
*/
protected int chunkSize(int n) {
int power = (n == 0 || n == 1)
? initialChunkPower
: Math.min(initialChunkPower + n - 1, AbstractSpinedBuffer.MAX_CHUNK_POWER);
return 1 << power;
}
/**
* Remove all data from the buffer
*/
public abstract void clear();
}