SequenceComparator.java
- /*
- * 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.diff;
- /**
- * Equivalence function for a {@link org.eclipse.jgit.diff.Sequence} compared by
- * difference algorithm.
- * <p>
- * Difference algorithms can use a comparator to compare portions of two
- * sequences and discover the minimal edits required to transform from one
- * sequence to the other sequence.
- * <p>
- * Indexes within a sequence are zero-based.
- *
- * @param <S>
- * type of sequence the comparator supports.
- */
- public abstract class SequenceComparator<S extends Sequence> {
- /**
- * Compare two items to determine if they are equivalent.
- *
- * It is permissible to compare sequence {@code a} with itself (by passing
- * {@code a} again in position {@code b}).
- *
- * @param a
- * the first sequence.
- * @param ai
- * item of {@code ai} to compare.
- * @param b
- * the second sequence.
- * @param bi
- * item of {@code bi} to compare.
- * @return true if the two items are identical according to this function's
- * equivalence rule.
- */
- public abstract boolean equals(S a, int ai, S b, int bi);
- /**
- * Get a hash value for an item in a sequence.
- *
- * If two items are equal according to this comparator's
- * {@link #equals(Sequence, int, Sequence, int)} method, then this hash
- * method must produce the same integer result for both items.
- *
- * It is not required for two items to have different hash values if they
- * are unequal according to the {@code equals()} method.
- *
- * @param seq
- * the sequence.
- * @param ptr
- * the item to obtain the hash for.
- * @return hash the hash value.
- */
- public abstract int hash(S seq, int ptr);
- /**
- * Modify the edit to remove common leading and trailing items.
- *
- * The supplied edit {@code e} is reduced in size by moving the beginning A
- * and B points so the edit does not cover any items that are in common
- * between the two sequences. The ending A and B points are also shifted to
- * remove common items from the end of the region.
- *
- * @param a
- * the first sequence.
- * @param b
- * the second sequence.
- * @param e
- * the edit to start with and update.
- * @return {@code e} if it was updated in-place, otherwise a new edit
- * containing the reduced region.
- */
- public Edit reduceCommonStartEnd(S a, S b, Edit e) {
- // Skip over items that are common at the start.
- //
- while (e.beginA < e.endA && e.beginB < e.endB
- && equals(a, e.beginA, b, e.beginB)) {
- e.beginA++;
- e.beginB++;
- }
- // Skip over items that are common at the end.
- //
- while (e.beginA < e.endA && e.beginB < e.endB
- && equals(a, e.endA - 1, b, e.endB - 1)) {
- e.endA--;
- e.endB--;
- }
- return e;
- }
- }