/*
* Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* - Neither the name of the Eclipse Foundation, Inc. nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.eclipse.jgit.internal.storage.file;
import java.text.MessageFormat;
import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.internal.storage.file.PackIndex.MutableEntry;
import org.eclipse.jgit.lib.ObjectId;
/**
* <p>
* Reverse index for forward pack index. Provides operations based on offset
* instead of object id. Such offset-based reverse lookups are performed in
* O(log n) time.
* </p>
*
* @see PackIndex
* @see PackFile
*/
public class PackReverseIndex {
/** Index we were created from, and that has our ObjectId data. */
private final PackIndex index;
/** The number of bytes per entry in the offsetIndex. */
private final long bucketSize;
/**
* An index into the nth mapping, where the value is the position after the
* the last index that contains the values of the bucket. For example given
* offset o (and bucket = o / bucketSize), the offset will be contained in
* the range nth[offsetIndex[bucket - 1]] inclusive to
* nth[offsetIndex[bucket]] exclusive.
*
* See {@link #binarySearch}
*/
private final int[] offsetIndex;
/** Mapping from indices in offset order to indices in SHA-1 order. */
private final int[] nth;
/**
* Create reverse index from straight/forward pack index, by indexing all
* its entries.
*
* @param packIndex
* forward index - entries to (reverse) index.
*/
public PackReverseIndex(final PackIndex packIndex) {
index = packIndex;
final long cnt = index.getObjectCount();
if (cnt + 1 > Integer.MAX_VALUE)
throw new IllegalArgumentException(
JGitText.get().hugeIndexesAreNotSupportedByJgitYet);
if (cnt == 0) {
bucketSize = Long.MAX_VALUE;
offsetIndex = new int[1];
nth = new int[0];
return;
}
final long[] offsetsBySha1 = new long[(int) cnt];
long maxOffset = 0;
int ith = 0;
for (final MutableEntry me : index) {
final long o = me.getOffset();
offsetsBySha1[ith++] = o;
if (o > maxOffset)
maxOffset = o;
}
bucketSize = maxOffset / cnt + 1;
int[] bucketIndex = new int[(int) cnt];
int[] bucketValues = new int[(int) cnt + 1];
for (int oi = 0; oi < offsetsBySha1.length; oi++) {
final long o = offsetsBySha1[oi];
final int bucket = (int) (o / bucketSize);
final int bucketValuesPos = oi + 1;
final int current = bucketIndex[bucket];
bucketIndex[bucket] = bucketValuesPos;
bucketValues[bucketValuesPos] = current;
}
int nthByOffset = 0;
nth = new int[offsetsBySha1.length];
offsetIndex = bucketIndex; // Reuse the allocation
for (int bi = 0; bi < bucketIndex.length; bi++) {
final int start = nthByOffset;
// Insertion sort of the values in the bucket.
for (int vi = bucketIndex[bi]; vi > 0; vi = bucketValues[vi]) {
final int nthBySha1 = vi - 1;
final long o = offsetsBySha1[nthBySha1];
int insertion = nthByOffset++;
for (; start < insertion; insertion--) {
if (o > offsetsBySha1[nth[insertion - 1]])
break;
nth[insertion] = nth[insertion - 1];
}
nth[insertion] = nthBySha1;
}
offsetIndex[bi] = nthByOffset;
}
}
/**
* Search for object id with the specified start offset in this pack
* (reverse) index.
*
* @param offset
* start offset of object to find.
* @return object id for this offset, or null if no object was found.
*/
public ObjectId findObject(final long offset) {
final int ith = binarySearch(offset);
if (ith < 0)
return null;
return index.getObjectId(nth[ith]);
}
/**
* Search for the next offset to the specified offset in this pack (reverse)
* index.
*
* @param offset
* start offset of previous object (must be valid-existing
* offset).
* @param maxOffset
* maximum offset in a pack (returned when there is no next
* offset).
* @return offset of the next object in a pack or maxOffset if provided
* offset was the last one.
* @throws CorruptObjectException
* when there is no object with the provided offset.
*/
public long findNextOffset(final long offset, final long maxOffset)
throws CorruptObjectException {
final int ith = binarySearch(offset);
if (ith < 0)
throw new CorruptObjectException(
MessageFormat.format(
JGitText.get().cantFindObjectInReversePackIndexForTheSpecifiedOffset,
Long.valueOf(offset)));
if (ith + 1 == nth.length)
return maxOffset;
return index.getOffset(nth[ith + 1]);
}
int findPostion(long offset) {
return binarySearch(offset);
}
private int binarySearch(final long offset) {
int bucket = (int) (offset / bucketSize);
int low = bucket == 0 ? 0 : offsetIndex[bucket - 1];
int high = offsetIndex[bucket];
while (low < high) {
final int mid = (low + high) >>> 1;
final long o = index.getOffset(nth[mid]);
if (offset < o)
high = mid;
else if (offset == o)
return mid;
else
low = mid + 1;
}
return -1;
}
ObjectId findObjectByPosition(int nthPosition) {
return index.getObjectId(nth[nthPosition]);
}
}