Let us quickly find ObjectId or next object for specified offset in a
pack, in O(log n) time.
Current implementation uses one level (reverse) indexing by an offset.
However, it tries to take small space as possible, by using 2 distinct
arrays for offsets with value < 2^31 (int[]) and those with value > 2^31
(long[]). Offsets are stored ordered in these 2 arrays. Binary search is
performed during requests.
Reverse index is constructed from an existing PackIndex instance, by
lazy initialization in a PackFile instance.
Signed-off-by: Marek Zawirski <marek.zawirski@xxxxxxxxx>
---
.../src/org/spearce/jgit/lib/PackFile.java | 20 +++
.../src/org/spearce/jgit/lib/PackReverseIndex.java | 179 ++++++++++++++++++++
2 files changed, 199 insertions(+), 0 deletions(-)
create mode 100644 org.spearce.jgit/src/org/spearce/jgit/lib/PackReverseIndex.java
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
index 1b2c167..3880966 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
@@ -55,6 +55,8 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
private final PackIndex idx;
+ private PackReverseIndex reverseIdx;
+
/**
* Construct a reader for an existing, pre-indexed packfile.
*
@@ -172,6 +174,18 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
return idx.getObjectCount();
}
+ /**
+ * Search for object id with the specified start offset in associated pack
+ * (reverse) index.
+ *
+ * @param offset
+ * start offset of object to find
+ * @return object id for this offset, or null if no object was found
+ */
+ ObjectId findObjectForOffset(final long offset) {
+ return getReverseIdx().findObject(offset);
+ }
+
final UnpackedObjectCache.Entry readCache(final long position) {
return UnpackedObjectCache.get(pack, position);
}
@@ -264,4 +278,10 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
throw new IOException("Unknown object type " + typeCode + ".");
}
}
+
+ private PackReverseIndex getReverseIdx() {
+ if (reverseIdx == null)
+ reverseIdx = new PackReverseIndex(idx);
+ return reverseIdx;
+ }
}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackReverseIndex.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackReverseIndex.java
new file mode 100644
index 0000000..3dede88
--- /dev/null
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackReverseIndex.java
@@ -0,0 +1,179 @@
+/*
+ * Copyright (C) 2008, Marek Zawirski <marek.zawirski@xxxxxxxxx>
+ *
+ * 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 Git Development Community 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.spearce.jgit.lib;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+import org.spearce.jgit.errors.CorruptObjectException;
+import org.spearce.jgit.lib.PackIndex.MutableEntry;
+
+/**
+ * <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
+ */
+class PackReverseIndex {
+ /**
+ * (offset31, truly) Offsets accommodating in 31 bits.
+ */
+ private final int offsets32[];
+
+ /**
+ * Offsets not accommodating in 31 bits.
+ */
+ private final long offsets64[];
+
+ /**
+ * Object ids corresponding to {@link #offsets32} and {@link #offsets64}.
+ */
+ private final int names[];
+
+ /**
+ * Create reverse index from straight/forward pack index, by indexing all
+ * its entries.
+ *
+ * @param index
+ * forward index - entries to (reverse) index.
+ */
+ PackReverseIndex(final PackIndex index) {
+ final long count = index.getObjectCount();
+ if (count > Integer.MAX_VALUE)
+ throw new IllegalArgumentException(
+ "Huge indexes (> 2^31 entries) are not supported by jgit, yet");
+
+ final MutableEntry entries[] = new MutableEntry[(int) count];
+ int i = 0;
+ int count32 = 0;
+ for (MutableEntry me : index) {
+ entries[i++] = me.cloneEntry();
+ if (me.getOffset() <= Integer.MAX_VALUE)
+ count32++;
+ }
+ Arrays.sort(entries, new Comparator<MutableEntry>() {
+ public int compare(MutableEntry o1, MutableEntry o2) {
+ return Long.signum(o1.getOffset() - o2.getOffset());
+ }
+ });
+
+ names = new int[entries.length * Constants.OBJECT_ID_LENGTH / 4];
+ offsets32 = new int[count32];
+ offsets64 = new long[entries.length - count32];
+ for (int j = 0, j32 = 0; j < entries.length; j++) {
+ final long offset = entries[j].getOffset();
+ if (offset <= Integer.MAX_VALUE)
+ offsets32[j32++] = (int) offset;
+ else
+ offsets64[j - j32] = offset;
+ entries[j].copyRawTo(names, j * Constants.OBJECT_ID_LENGTH / 4);
+ }
+ }
+
+ /**
+ * 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.
+ */
+ ObjectId findObject(final long offset) {
+ if (offset <= Integer.MAX_VALUE) {
+ final int i32 = Arrays.binarySearch(offsets32, (int) offset);
+ if (i32 < 0)
+ return null;
+ final int iNames = i32 * Constants.OBJECT_ID_LENGTH / 4;
+ return ObjectId.fromRaw(names, iNames);
+ } else {
+ final int i64 = Arrays.binarySearch(offsets64, offset);
+ if (i64 < 0)
+ return null;
+ final int iNames = (i64 + offsets32.length)
+ * Constants.OBJECT_ID_LENGTH / 4;
+ return ObjectId.fromRaw(names, iNames);
+ }
+ }
+
+ /**
+ * 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.
+ */
+ long findNextOffset(final long offset, final long maxOffset)
+ throws CorruptObjectException {
+ if (offset <= Integer.MAX_VALUE) {
+ final int i32 = Arrays.binarySearch(offsets32, (int) offset);
+ if (i32 < 0)
+ throw new CorruptObjectException(
+ "Can't find object in (reverse) pack index for the specified offset "
+ + offset);
+
+ if (i32 + 1 == offsets32.length) {
+ if (offsets64.length > 0)
+ return offsets64[0];
+ return maxOffset;
+ }
+ return offsets32[i32 + 1];
+ } else {
+ final int i64 = Arrays.binarySearch(offsets64, offset);
+ if (i64 < 0)
+ throw new CorruptObjectException(
+ "Can't find object in (reverse) pack index for the specified offset "
+ + offset);
+
+ if (i64 + 1 == offsets64.length)
+ return maxOffset;
+ return offsets64[i64 + 1];
+ }
+ }
+}
--
1.5.5.1
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