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 * Copyright (C) 2010, Google Inc.
 * and other copyright owners as documented in the project's IP log.
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 * This program and the accompanying materials are made available
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package org.eclipse.jgit.diff;

/**
 * Wrap another comparator for use with {@link Subsequence}.
 * <p>
 * This comparator acts as a proxy for the real comparator, translating element
 * indexes on the fly by adding the subsequence's begin offset to them.
 * Comparators of this type must be used with a {@link Subsequence}.
 *
 * @param <S>
 *            the base sequence type.
 */
public final class SubsequenceComparator<S extends Sequence> extends
		SequenceComparator<Subsequence<S>> {
	private final SequenceComparator<? super S> cmp;

	/**
	 * Construct a comparator wrapping another comparator.
	 *
	 * @param cmp
	 *            the real comparator.
	 */
	public SubsequenceComparator(SequenceComparator<? super S> cmp) {
		this.cmp = cmp;
	}

	@Override
	public boolean equals(Subsequence<S> a, int ai, Subsequence<S> b, int bi) {
		return cmp.equals(a.base, ai + a.begin, b.base, bi + b.begin);
	}

	@Override
	public int hash(Subsequence<S> seq, int ptr) {
		return cmp.hash(seq.base, ptr + seq.begin);
	}
}