--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/tmatesoft/hg/internal/RevisionLookup.java	Fri May 03 17:03:31 2013 +0200
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2013 TMate Software Ltd
+ *  
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * For information on how to redistribute this software under
+ * the terms of a license other than GNU General Public License
+ * contact TMate Software at support@hg4j.com
+ */
+package org.tmatesoft.hg.internal;
+
+import static org.tmatesoft.hg.repo.HgRepository.BAD_REVISION;
+
+import java.util.Arrays;
+
+import org.tmatesoft.hg.core.Nodeid;
+import org.tmatesoft.hg.repo.HgRevisionMap;
+
+/**
+ * Lite alternative to {@link HgRevisionMap}, to speed up nodeid to index conversion without consuming too much memory.
+ * E.g. for a 100k revisions, {@link HgRevisionMap} consumes 3 * (N * sizeof(int)) for indexes plus 48 bytes per 
+ * Nodeid instance, total (12+48)*N = 6 mb of memory. {RevisionLookup} instead keeps only Nodeid hashes, (N * sizeof(int) = 400 kb),
+ * but is slower in lookup, O(N/2) to find potential match plus disk read operatin (or few, in an unlikely case of hash collisions).
+ * 
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+public class RevisionLookup implements RevlogStream.Inspector {
+	
+	private final RevlogStream content;
+	private int[] nodeidHashes;
+
+	public RevisionLookup(RevlogStream stream) {
+		assert stream != null;
+		content = stream;
+	}
+	
+	public static RevisionLookup createFor(RevlogStream stream) {
+		RevisionLookup rv = new RevisionLookup(stream);
+		int revCount = stream.revisionCount();
+		rv.prepare(revCount);
+		if (revCount > 0) {
+			stream.iterate(0, revCount - 1, false, rv);
+		}
+		return rv;
+	}
+
+	public void prepare(int count) {
+		nodeidHashes = new int[count];
+		Arrays.fill(nodeidHashes, BAD_REVISION);
+	}
+	public void next(int index, byte[] nodeid) {
+		nodeidHashes[index] = Nodeid.hashCode(nodeid);
+	}
+	public void next(int index, Nodeid nodeid) {
+		nodeidHashes[index] = nodeid.hashCode();
+	}
+	public int findIndex(Nodeid nodeid) {
+		final int hash = nodeid.hashCode();
+		for (int i = 0; i < nodeidHashes.length; i++) {
+			if (nodeidHashes[i] == hash) {
+				byte[] nodeidAtI = content.nodeid(i);
+				if (nodeid.equalsTo(nodeidAtI)) {
+					return i;
+				}
+			}
+			// else: false match (only 4 head bytes matched, continue loop
+		}
+		return BAD_REVISION;
+	}
+
+	public void next(int revisionIndex, int actualLen, int baseRevision, int linkRevision, int parent1Revision, int parent2Revision, byte[] nodeid, DataAccess data) {
+		next(revisionIndex, nodeid);
+	}
+}