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/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
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 * 	contributors may be used to endorse or promote products derived from this
 * 	software without specific prior written permission.
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package org.openimaj.lsh.functions;

import cern.jet.random.engine.MersenneTwister;

import org.openimaj.feature.LongFV;
import org.openimaj.feature.SparseLongFV;
import org.openimaj.util.array.SparseLongArray;

/**
 * Base {@link RandomisedHashFunction} for hashing long arrays.
 * 
 * @author Jonathon Hare ([email protected])
 */
public abstract class LongHashFunction extends RandomisedHashFunction {
	/**
	 * Default constructor
	 * 
	 * @param factory
	 *            factory to use
	 * @param rng
	 *            random generator
	 */
	LongHashFunction(MersenneTwister rng) {
		super(rng);
	}
	
	/**
	 * Compute the hash code for the feature vector.
	 * 
	 * @param feature
	 *            the feature vector
	 * 
	 * @return the hash code
	 */
	public final int computeHashCode(LongFV feature) {
		return computeHashCode(feature.values);
	}
	
	/**
	 * Compute the hash code for the sparse array. This method 
	 * converts the sparse array to a dense one and computes the
	 * hash code from that. Subclasses should override this method
	 * for improved performance.
	 * 
	 * @param array
	 *            the sparse array
	 * 
	 * @return the hash code
	 */
	public int computeHashCode(SparseLongArray array) {
		return computeHashCode(array.toArray());
	}
	
	/**
	 * Compute the hash code for the sparse feature vector.
	 * 
	 * @param feature
	 *            the sparse feature
	 * 
	 * @return the hash code
	 */
	public final int computeHashCode(SparseLongFV feature) {
		return computeHashCode(feature.values);
	}
}