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/*
* Copyright (C) 2009, Google Inc.
* Copyright (C) 2009, Jonas Fonseca <fonseca@diku.dk>
* Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0 which is available at
* https://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.eclipse.jgit.revwalk;
import java.text.MessageFormat;
import java.util.AbstractList;
import org.eclipse.jgit.internal.JGitText;
/**
* An ordered list of {@link org.eclipse.jgit.revwalk.RevObject} subclasses.
*
* @param <E>
* type of subclass of RevObject the list is storing.
*/
public class RevObjectList<E extends RevObject> extends AbstractList<E> {
static final int BLOCK_SHIFT = 8;
static final int BLOCK_SIZE = 1 << BLOCK_SHIFT;
/**
* Items stored in this list.
* <p>
* If {@link Block#shift} = 0 this block holds the list elements; otherwise
* it holds pointers to other {@link Block} instances which use a shift that
* is {@link #BLOCK_SHIFT} smaller.
*/
protected Block contents = new Block(0);
/** Current number of elements in the list. */
protected int size = 0;
/**
* Create an empty object list.
*/
public RevObjectList() {
// Initialized above.
}
@Override
public void add(int index, E element) {
if (index != size)
throw new UnsupportedOperationException(MessageFormat.format(
JGitText.get().unsupportedOperationNotAddAtEnd,
Integer.valueOf(index)));
set(index, element);
size++;
}
@Override
@SuppressWarnings("unchecked")
public E set(int index, E element) {
Block s = contents;
while (index >> s.shift >= BLOCK_SIZE) {
s = new Block(s.shift + BLOCK_SHIFT);
s.contents[0] = contents;
contents = s;
}
while (s.shift > 0) {
final int i = index >> s.shift;
index -= i << s.shift;
if (s.contents[i] == null)
s.contents[i] = new Block(s.shift - BLOCK_SHIFT);
s = (Block) s.contents[i];
}
final Object old = s.contents[index];
s.contents[index] = element;
return (E) old;
}
@Override
@SuppressWarnings("unchecked")
public E get(int index) {
Block s = contents;
if (index >> s.shift >= 1024)
return null;
while (s != null && s.shift > 0) {
final int i = index >> s.shift;
index -= i << s.shift;
s = (Block) s.contents[i];
}
return s != null ? (E) s.contents[index] : null;
}
@Override
public int size() {
return size;
}
@Override
public void clear() {
contents = new Block(0);
size = 0;
}
/** One level of contents, either an intermediate level or a leaf level. */
protected static class Block {
final Object[] contents = new Object[BLOCK_SIZE];
final int shift;
Block(int s) {
shift = s;
}
}
}
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