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    * and other copyright owners as documented in the project's IP log.
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  package org.eclipse.jgit.diff;
  
  import static org.eclipse.jgit.diff.DiffEntry.Side.NEW;
  import static org.eclipse.jgit.diff.DiffEntry.Side.OLD;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.BitSet;
  import java.util.List;
  
  import org.eclipse.jgit.diff.DiffEntry.ChangeType;
  import org.eclipse.jgit.diff.SimilarityIndex.TableFullException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.FileMode;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ProgressMonitor;
  
  class SimilarityRenameDetector {
  	/**
  	 * Number of bits we need to express an index into src or dst list.
  	 * <p>
  	 * This must be 28, giving us a limit of 2^28 entries in either list, which
  	 * is an insane limit of 536,870,912 file names being considered in a single
  	 * rename pass. The other 8 bits are used to store the score, while staying
  	 * under 127 so the long doesn't go negative.
  	 */
  	private static final int BITS_PER_INDEX = 28;
  
  	private static final int INDEX_MASK = (1 << BITS_PER_INDEX) - 1;
  
  	private static final int SCORE_SHIFT = 2 * BITS_PER_INDEX;
  
  	private ContentSource.Pair reader;
  
  	/**
  	 * All sources to consider for copies or renames.
  	 * <p>
  	 * A source is typically a {@link ChangeType#DELETE} change, but could be
  	 * another type when trying to perform copy detection concurrently with
  	 * rename detection.
  	 */
  	private List<DiffEntry> srcs;
  
  	/**
  	 * All destinations to consider looking for a rename.
  	 * <p>
  	 * A destination is typically an {@link ChangeType#ADD}, as the name has
  	 * just come into existence, and we want to discover where its initial
  	 * content came from.
  	 */
  	private List<DiffEntry> dsts;
  
  	/**
  	 * Matrix of all examined file pairs, and their scores.
  	 * <p>
 	 * The upper 8 bits of each long stores the score, but the score is bounded
 	 * to be in the range (0, 128] so that the highest bit is never set, and all
 	 * entries are therefore positive.
 	 * <p>
 	 * List indexes to an element of {@link #srcs} and {@link #dsts} are encoded
 	 * as the lower two groups of 28 bits, respectively, but the encoding is
 	 * inverted, so that 0 is expressed as {@code (1 << 28) - 1}. This sorts
 	 * lower list indices later in the matrix, giving precedence to files whose
 	 * names sort earlier in the tree.
 	 */
 	private long[] matrix;
 
 	/** Score a pair must exceed to be considered a rename. */
 	private int renameScore = 60;
 
 	/** Set if any {@link SimilarityIndex.TableFullException} occurs. */
 	private boolean tableOverflow;
 
 	private List<DiffEntry> out;
 
 	SimilarityRenameDetector(ContentSource.Pair reader, List<DiffEntry> srcs,
 			List<DiffEntry> dsts) {
 		this.reader = reader;
 		this.srcs = srcs;
 		this.dsts = dsts;
 	}
 
 	void setRenameScore(int score) {
 		renameScore = score;
 	}
 
 	void compute(ProgressMonitor pm) throws IOException {
 		if (pm == null)
 			pm = NullProgressMonitor.INSTANCE;
 
 		pm.beginTask(JGitText.get().renamesFindingByContent, //
 				2 * srcs.size() * dsts.size());
 
 		int mNext = buildMatrix(pm);
 		out = new ArrayList<DiffEntry>(Math.min(mNext, dsts.size()));
 
 		// Match rename pairs on a first come, first serve basis until
 		// we have looked at everything that is above our minimum score.
 		//
 		for (--mNext; mNext >= 0; mNext--) {
 			long ent = matrix[mNext];
 			int sIdx = srcFile(ent);
 			int dIdx = dstFile(ent);
 			DiffEntry s = srcs.get(sIdx);
 			DiffEntry d = dsts.get(dIdx);
 
 			if (d == null) {
 				pm.update(1);
 				continue; // was already matched earlier
 			}
 
 			ChangeType type;
 			if (s.changeType == ChangeType.DELETE) {
 				// First use of this source file. Tag it as a rename so we
 				// later know it is already been used as a rename, other
 				// matches (if any) will claim themselves as copies instead.
 				//
 				s.changeType = ChangeType.RENAME;
 				type = ChangeType.RENAME;
 			} else {
 				type = ChangeType.COPY;
 			}
 
 			out.add(DiffEntry.pair(type, s, d, score(ent)));
 			dsts.set(dIdx, null); // Claim the destination was matched.
 			pm.update(1);
 		}
 
 		srcs = compactSrcList(srcs);
 		dsts = compactDstList(dsts);
 		pm.endTask();
 	}
 
 	List<DiffEntry> getMatches() {
 		return out;
 	}
 
 	List<DiffEntry> getLeftOverSources() {
 		return srcs;
 	}
 
 	List<DiffEntry> getLeftOverDestinations() {
 		return dsts;
 	}
 
 	boolean isTableOverflow() {
 		return tableOverflow;
 	}
 
 	private static List<DiffEntry> compactSrcList(List<DiffEntry> in) {
 		ArrayList<DiffEntry> r = new ArrayList<DiffEntry>(in.size());
 		for (DiffEntry e : in) {
 			if (e.changeType == ChangeType.DELETE)
 				r.add(e);
 		}
 		return r;
 	}
 
 	private static List<DiffEntry> compactDstList(List<DiffEntry> in) {
 		ArrayList<DiffEntry> r = new ArrayList<DiffEntry>(in.size());
 		for (DiffEntry e : in) {
 			if (e != null)
 				r.add(e);
 		}
 		return r;
 	}
 
 	private int buildMatrix(ProgressMonitor pm) throws IOException {
 		// Allocate for the worst-case scenario where every pair has a
 		// score that we need to consider. We might not need that many.
 		//
 		matrix = new long[srcs.size() * dsts.size()];
 
 		long[] srcSizes = new long[srcs.size()];
 		long[] dstSizes = new long[dsts.size()];
 		BitSet dstTooLarge = null;
 
 		// Consider each pair of files, if the score is above the minimum
 		// threshold we need record that scoring in the matrix so we can
 		// later find the best matches.
 		//
 		int mNext = 0;
 		SRC: for (int srcIdx = 0; srcIdx < srcs.size(); srcIdx++) {
 			DiffEntry srcEnt = srcs.get(srcIdx);
 			if (!isFile(srcEnt.oldMode)) {
 				pm.update(dsts.size());
 				continue;
 			}
 
 			SimilarityIndex s = null;
 
 			for (int dstIdx = 0; dstIdx < dsts.size(); dstIdx++) {
 				DiffEntry dstEnt = dsts.get(dstIdx);
 
 				if (!isFile(dstEnt.newMode)) {
 					pm.update(1);
 					continue;
 				}
 
 				if (!RenameDetector.sameType(srcEnt.oldMode, dstEnt.newMode)) {
 					pm.update(1);
 					continue;
 				}
 
 				if (dstTooLarge != null && dstTooLarge.get(dstIdx)) {
 					pm.update(1);
 					continue;
 				}
 
 				long srcSize = srcSizes[srcIdx];
 				if (srcSize == 0) {
 					srcSize = size(OLD, srcEnt) + 1;
 					srcSizes[srcIdx] = srcSize;
 				}
 
 				long dstSize = dstSizes[dstIdx];
 				if (dstSize == 0) {
 					dstSize = size(NEW, dstEnt) + 1;
 					dstSizes[dstIdx] = dstSize;
 				}
 
 				long max = Math.max(srcSize, dstSize);
 				long min = Math.min(srcSize, dstSize);
 				if (min * 100 / max < renameScore) {
 					// Cannot possibly match, as the file sizes are so different
 					pm.update(1);
 					continue;
 				}
 
 				if (s == null) {
 					try {
 						s = hash(OLD, srcEnt);
 					} catch (TableFullException tableFull) {
 						tableOverflow = true;
 						continue SRC;
 					}
 				}
 
 				SimilarityIndex d;
 				try {
 					d = hash(NEW, dstEnt);
 				} catch (TableFullException tableFull) {
 					if (dstTooLarge == null)
 						dstTooLarge = new BitSet(dsts.size());
 					dstTooLarge.set(dstIdx);
 					tableOverflow = true;
 					pm.update(1);
 					continue;
 				}
 
 				int contentScore = s.score(d, 10000);
 
 				// nameScore returns a value between 0 and 100, but we want it
 				// to be in the same range as the content score. This allows it
 				// to be dropped into the pretty formula for the final score.
 				int nameScore = nameScore(srcEnt.oldPath, dstEnt.newPath) * 100;
 
 				int score = (contentScore * 99 + nameScore * 1) / 10000;
 
 				if (score < renameScore) {
 					pm.update(1);
 					continue;
 				}
 
 				matrix[mNext++] = encode(score, srcIdx, dstIdx);
 				pm.update(1);
 			}
 		}
 
 		// Sort everything in the range we populated, which might be the
 		// entire matrix, or just a smaller slice if we had some bad low
 		// scoring pairs.
 		//
 		Arrays.sort(matrix, 0, mNext);
 		return mNext;
 	}
 
 	static int nameScore(String a, String b) {
 	    int aDirLen = a.lastIndexOf("/") + 1; //$NON-NLS-1$
 	    int bDirLen = b.lastIndexOf("/") + 1; //$NON-NLS-1$
 
 	    int dirMin = Math.min(aDirLen, bDirLen);
 	    int dirMax = Math.max(aDirLen, bDirLen);
 
 	    final int dirScoreLtr;
 	    final int dirScoreRtl;
 
 		if (dirMax == 0) {
 			dirScoreLtr = 100;
 			dirScoreRtl = 100;
 		} else {
 			int dirSim = 0;
 			for (; dirSim < dirMin; dirSim++) {
 				if (a.charAt(dirSim) != b.charAt(dirSim))
 					break;
 			}
 			dirScoreLtr = (dirSim * 100) / dirMax;
 
 			if (dirScoreLtr == 100) {
 				dirScoreRtl = 100;
 			} else {
 				for (dirSim = 0; dirSim < dirMin; dirSim++) {
 					if (a.charAt(aDirLen - 1 - dirSim) != b.charAt(bDirLen - 1
 							- dirSim))
 						break;
 				}
 				dirScoreRtl = (dirSim * 100) / dirMax;
 			}
 		}
 
 		int fileMin = Math.min(a.length() - aDirLen, b.length() - bDirLen);
 		int fileMax = Math.max(a.length() - aDirLen, b.length() - bDirLen);
 
 		int fileSim = 0;
 		for (; fileSim < fileMin; fileSim++) {
 			if (a.charAt(a.length() - 1 - fileSim) != b.charAt(b.length() - 1
 					- fileSim))
 				break;
 		}
 		int fileScore = (fileSim * 100) / fileMax;
 
 		return (((dirScoreLtr + dirScoreRtl) * 25) + (fileScore * 50)) / 100;
 	}
 
 	private SimilarityIndex hash(DiffEntry.Side side, DiffEntry ent)
 			throws IOException, TableFullException {
 		SimilarityIndex r = new SimilarityIndex();
 		r.hash(reader.open(side, ent));
 		r.sort();
 		return r;
 	}
 
 	private long size(DiffEntry.Side side, DiffEntry ent) throws IOException {
 		return reader.size(side, ent);
 	}
 
 	private static int score(long value) {
 		return (int) (value >>> SCORE_SHIFT);
 	}
 
 	static int srcFile(long value) {
 		return decodeFile(((int) (value >>> BITS_PER_INDEX)) & INDEX_MASK);
 	}
 
 	static int dstFile(long value) {
 		return decodeFile(((int) value) & INDEX_MASK);
 	}
 
 	static long encode(int score, int srcIdx, int dstIdx) {
 		return (((long) score) << SCORE_SHIFT) //
 				| (encodeFile(srcIdx) << BITS_PER_INDEX) //
 				| encodeFile(dstIdx);
 	}
 
 	private static long encodeFile(int idx) {
 		// We invert the index so that the first file in the list sorts
 		// later in the table. This permits us to break ties favoring
 		// earlier names over later ones.
 		//
 		return INDEX_MASK - idx;
 	}
 
 	private static int decodeFile(int v) {
 		return INDEX_MASK - v;
 	}
 
 	private static boolean isFile(FileMode mode) {
 		return (mode.getBits() & FileMode.TYPE_MASK) == FileMode.TYPE_FILE;
 	}
 }