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- /*
- * Copyright (C) 2010, Google Inc.
- * 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.pack;
-
- /**
- * Supports {@link DeltaIndex} by performing a partial scan of the content.
- */
- class DeltaIndexScanner {
- final int[] table;
-
- // To save memory the buckets for hash chains are stored in correlated
- // arrays. This permits us to get 3 values per entry, without paying
- // the penalty for an object header on each entry.
-
- final long[] entries;
-
- final int[] next;
-
- final int tableMask;
-
- private int entryCnt;
-
- DeltaIndexScanner(byte[] raw, int len) {
- // Clip the length so it falls on a block boundary. We won't
- // bother to scan the final partial block.
- //
- len -= (len % DeltaIndex.BLKSZ);
-
- final int worstCaseBlockCnt = len / DeltaIndex.BLKSZ;
- if (worstCaseBlockCnt < 1) {
- table = new int[] {};
- tableMask = 0;
-
- entries = new long[] {};
- next = new int[] {};
-
- } else {
- table = new int[tableSize(worstCaseBlockCnt)];
- tableMask = table.length - 1;
-
- // As we insert blocks we preincrement so that 0 is never a
- // valid entry. Therefore we have to allocate one extra space.
- //
- entries = new long[1 + worstCaseBlockCnt];
- next = new int[entries.length];
-
- scan(raw, len);
- }
- }
-
- private void scan(byte[] raw, final int end) {
- // We scan the input backwards, and always insert onto the
- // front of the chain. This ensures that chains will have lower
- // offsets at the front of the chain, allowing us to prefer the
- // earlier match rather than the later match.
- //
- int lastHash = 0;
- int ptr = end - DeltaIndex.BLKSZ;
- do {
- final int key = DeltaIndex.hashBlock(raw, ptr);
- final int tIdx = key & tableMask;
-
- final int head = table[tIdx];
- if (head != 0 && lastHash == key) {
- // Two consecutive blocks have the same content hash,
- // prefer the earlier block because we want to use the
- // longest sequence we can during encoding.
- //
- entries[head] = (((long) key) << 32) | ptr;
- } else {
- final int eIdx = ++entryCnt;
- entries[eIdx] = (((long) key) << 32) | ptr;
- next[eIdx] = head;
- table[tIdx] = eIdx;
- }
-
- lastHash = key;
- ptr -= DeltaIndex.BLKSZ;
- } while (0 <= ptr);
- }
-
- private static int tableSize(final int worstCaseBlockCnt) {
- int shift = 32 - Integer.numberOfLeadingZeros(worstCaseBlockCnt);
- int sz = 1 << (shift - 1);
- if (sz < worstCaseBlockCnt)
- sz <<= 1;
- return sz;
- }
- }
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