org.eclipse.jgit/src/org/eclipse/jgit/diff/HashedSequencePair.java

/*
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 * This program and the accompanying materials are made available
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package org.eclipse.jgit.diff;

/**
 * Wraps two {@link Sequence} instances to cache their element hash codes.
 * <p>
 * This pair wraps two sequences that contain cached hash codes for the input
 * sequences.
 *
 * @param <S>
 *            the base sequence type.
 */
public class HashedSequencePair<S extends Sequence> {
	private final SequenceComparator<? super S> cmp;

	private final S baseA;

	private final S baseB;

	private HashedSequence<S> cachedA;

	private HashedSequence<S> cachedB;

	/**
	 * Construct a pair to provide fast hash codes.
	 *
	 * @param cmp
	 *            the base comparator for the sequence elements.
	 * @param a
	 *            the A sequence.
	 * @param b
	 *            the B sequence.
	 */
	public HashedSequencePair(SequenceComparator<? super S> cmp, S a, S b) {
		this.cmp = cmp;
		this.baseA = a;
		this.baseB = b;
	}

	/** @return obtain a comparator that uses the cached hash codes. */
	public HashedSequenceComparator<S> getComparator() {
		return new HashedSequenceComparator<>(cmp);
	}

	/** @return wrapper around A that includes cached hash codes. */
	public HashedSequence<S> getA() {
		if (cachedA == null)
			cachedA = wrap(baseA);
		return cachedA;
	}

	/** @return wrapper around B that includes cached hash codes. */
	public HashedSequence<S> getB() {
		if (cachedB == null)
			cachedB = wrap(baseB);
		return cachedB;
	}

	private HashedSequence<S> wrap(S base) {
		final int end = base.size();
		final int[] hashes = new int[end];
		for (int ptr = 0; ptr < end; ptr++)
			hashes[ptr] = cmp.hash(base, ptr);
		return new HashedSequence<>(base, hashes);
	}
}