| /* |
| * Copyright (C) 2010, Google Inc. and others |
| * |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Distribution License v. 1.0 which is available at |
| * https://www.eclipse.org/org/documents/edl-v10.php. |
| * |
| * SPDX-License-Identifier: BSD-3-Clause |
| */ |
| |
| 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; |
| } |
| } |