DeltaWindowEntry.java

/*
 * Copyright (C) 2010, Google Inc. 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.internal.storage.pack;

final class DeltaWindowEntry {
    DeltaWindowEntry prev;
    DeltaWindowEntry next;
    ObjectToPack object;

    /** Complete contents of this object. Lazily loaded. */
    byte[] buffer;

    /** Index of this object's content, to encode other deltas. Lazily loaded. */
    DeltaIndex index;

    final void set(ObjectToPack object) {
        this.object = object;
        this.index = null;
        this.buffer = null;
    }

    /** @return current delta chain depth of this object. */
    final int depth() {
        return object.getDeltaDepth();
    }

    /** @return type of the object in this window entry. */
    final int type() {
        return object.getType();
    }

    /** @return estimated unpacked size of the object, in bytes . */
    final int size() {
        return object.getWeight();
    }

    /** @return true if there is no object stored in this entry. */
    final boolean empty() {
        return object == null;
    }

    final void makeNext(DeltaWindowEntry e) {
        // Disconnect e from the chain.
        e.prev.next = e.next;
        e.next.prev = e.prev;

        // Insert e after this.
        e.next = next;
        e.prev = this;
        next.prev = e;
        next = e;
    }

    static DeltaWindowEntry createWindow(int cnt) {
        // C Git increases the window size supplied by the user by 1.
        // We don't know why it does this, but if the user asks for
        // window=10, it actually processes with window=11. Because
        // the window size has the largest direct impact on the final
        // pack file size, we match this odd behavior here to give us
        // a better chance of producing a similar sized pack as C Git.
        //
        // We would prefer to directly honor the user's request since
        // PackWriter has a minimum of 2 for the window size, but then
        // users might complain that JGit is creating a bigger pack file.
        DeltaWindowEntry res = new DeltaWindowEntry();
        DeltaWindowEntry p = res;
        for (int i = 0; i < cnt; i++) {
            DeltaWindowEntry e = new DeltaWindowEntry();
            e.prev = p;
            p.next = e;
            p = e;
        }
        p.next = res;
        res.prev = p;
        return res;
    }
}