| /* |
| * Copyright (C) 2023, Google LLC 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.file; |
| |
| import java.text.MessageFormat; |
| |
| import org.eclipse.jgit.errors.CorruptObjectException; |
| import org.eclipse.jgit.errors.PackMismatchException; |
| import org.eclipse.jgit.internal.JGitText; |
| import org.eclipse.jgit.internal.storage.file.PackIndex.MutableEntry; |
| import org.eclipse.jgit.lib.ObjectId; |
| |
| /** |
| * Reverse index for forward pack index which is computed from the forward pack |
| * index. |
| * <p> |
| * Creating an instance uses an insertion sort of the entries in the forward |
| * index, so it runs in quadratic time on average. |
| */ |
| final class PackReverseIndexComputed implements PackReverseIndex { |
| /** |
| * Index we were created from, and that has our ObjectId data. |
| */ |
| private final PackIndex index; |
| |
| /** |
| * The difference in offset between the start of an offset bucket and the |
| * start of its succeeding bucket. |
| */ |
| private final long bucketSize; |
| |
| /** |
| * The indexes into indexPosInOffsetOrder at which the next bucket starts. |
| * <p> |
| * For example, given offset o (and therefore bucket = o / bucketSize), the |
| * indexPos corresponding to o will be contained in the range |
| * indexPosInOffsetOrder[nextBucketStart[bucket - 1]] inclusive to |
| * indexPosInOffsetOrder[nextBucketStart[bucket]] exclusive. |
| * <p> |
| * This range information can speed up #binarySearch by identifying the |
| * relevant bucket and only searching within its range. |
| * <p> |
| * See {@link #binarySearch} |
| */ |
| private final int[] nextBucketStart; |
| |
| /** |
| * Mapping from indices in offset order to indices in SHA-1 order. |
| */ |
| private final int[] indexPosInOffsetOrder; |
| |
| /** |
| * Create reverse index from straight/forward pack index, by indexing all |
| * its entries. |
| * |
| * @param packIndex |
| * forward index - entries to (reverse) index. |
| */ |
| PackReverseIndexComputed(PackIndex packIndex) { |
| index = packIndex; |
| |
| long rawCnt = index.getObjectCount(); |
| if (rawCnt + 1 > Integer.MAX_VALUE) { |
| throw new IllegalArgumentException( |
| JGitText.get().hugeIndexesAreNotSupportedByJgitYet); |
| } |
| int cnt = (int) rawCnt; |
| |
| if (cnt == 0) { |
| bucketSize = Long.MAX_VALUE; |
| nextBucketStart = new int[1]; |
| indexPosInOffsetOrder = new int[0]; |
| return; |
| } |
| |
| // Sort the index positions according to the corresponding pack offsets. |
| // Use bucket sort since the offsets are somewhat uniformly distributed |
| // over the range (0, pack size). |
| long[] offsetsInIndexOrder = new long[cnt]; |
| long maxOffset = 0; |
| int i = 0; |
| for (MutableEntry entry : index) { |
| long offset = entry.getOffset(); |
| offsetsInIndexOrder[i++] = offset; |
| if (offset > maxOffset) { |
| maxOffset = offset; |
| } |
| } |
| |
| bucketSize = maxOffset / cnt + 1; |
| // The values in each bucket, stored as a linked list. Given a bucket, |
| // headValues[bucket] contains the first value, |
| // furtherValues[headValues[bucket]] contains the second, |
| // furtherValues[furtherValues[headValues[bucket]]] the third, and so |
| // on. The linked list stops when a value is 0. The values themselves |
| // are shifted index positions. There won't be any |
| // collisions because every index position is unique. |
| int[] headValues = new int[cnt]; |
| int[] furtherValues = new int[cnt + 1]; |
| for (int indexPos = 0; indexPos < cnt; indexPos++) { |
| // The offset determines which bucket this index position falls |
| // into, since the goal is sort into offset order. |
| long offset = offsetsInIndexOrder[indexPos]; |
| int bucket = (int) (offset / bucketSize); |
| // Store the index positions as 1-indexed so that default |
| // initialized value 0 can be interpreted as the end of the bucket |
| // values. |
| int asBucketValue = indexPos + 1; |
| // If there is an existing value in this bucket, push the value to |
| // the front of the linked list. |
| int current = headValues[bucket]; |
| headValues[bucket] = asBucketValue; |
| furtherValues[asBucketValue] = current; |
| } |
| |
| int nthByOffset = 0; |
| indexPosInOffsetOrder = new int[cnt]; |
| nextBucketStart = headValues; // Reuse the allocation |
| for (int bi = 0; bi < headValues.length; bi++) { |
| // Insertion sort of the values in the bucket. |
| int start = nthByOffset; |
| for (int vi = headValues[bi]; vi > 0; vi = furtherValues[vi]) { |
| int nthBySha1 = vi - 1; |
| long o = offsetsInIndexOrder[nthBySha1]; |
| int insertion = nthByOffset++; |
| for (; start < insertion; insertion--) { |
| if (o > offsetsInIndexOrder[indexPosInOffsetOrder[insertion |
| - 1]]) { |
| break; |
| } |
| indexPosInOffsetOrder[insertion] = indexPosInOffsetOrder[insertion |
| - 1]; |
| } |
| indexPosInOffsetOrder[insertion] = nthBySha1; |
| } |
| nextBucketStart[bi] = nthByOffset; |
| } |
| } |
| |
| @Override |
| public void verifyPackChecksum(String packFilePath) |
| throws PackMismatchException { |
| // There is no file with a checksum. |
| } |
| |
| @Override |
| public ObjectId findObject(long offset) { |
| final int ith = binarySearch(offset); |
| if (ith < 0) { |
| return null; |
| } |
| return index.getObjectId(indexPosInOffsetOrder[ith]); |
| } |
| |
| @Override |
| public long findNextOffset(long offset, 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 == indexPosInOffsetOrder.length) { |
| return maxOffset; |
| } |
| return index.getOffset(indexPosInOffsetOrder[ith + 1]); |
| } |
| |
| @Override |
| public int findPosition(long offset) { |
| return binarySearch(offset); |
| } |
| |
| private int binarySearch(long offset) { |
| int bucket = (int) (offset / bucketSize); |
| int low = bucket == 0 ? 0 : nextBucketStart[bucket - 1]; |
| int high = nextBucketStart[bucket]; |
| while (low < high) { |
| final int mid = (low + high) >>> 1; |
| final long o = index.getOffset(indexPosInOffsetOrder[mid]); |
| if (offset < o) { |
| high = mid; |
| } else if (offset == o) { |
| return mid; |
| } else { |
| low = mid + 1; |
| } |
| } |
| return -1; |
| } |
| |
| @Override |
| public ObjectId findObjectByPosition(int nthPosition) { |
| return index.getObjectId(indexPosInOffsetOrder[nthPosition]); |
| } |
| } |