literallysignedminimalperfecthash.java

MG4J (Managing Gigabytes for Java) is a free full-text search engine for large document collections

package it.unimi.dsi.mg4j.util;

/*		 
 * MG4J: Managing Gigabytes for Java
 *
 * Copyright (C) 2002-2007 Sebastiano Vigna 
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 2.1 of the License, or (at your option)
 *  any later version.
 *
 *  This library is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 *  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 */

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.InvocationTargetException;
import java.util.Iterator;

import com.martiansoftware.jsap.JSAPException;


/** Literally signed order-preserving minimal perfect hash tables.
 *
 * <P>This class source exemplifies a signed minimal perfect hash table that
 * signes each term with the term itself, thus avoiding false positives. Note
 * that it does not feature {@linkplain SignedMinimalPerfectHash#SignedMinimalPerfectHash(String, String, int, boolean) constructors for <samp>gzip</samp>'d files}.
 * 
 * @author Sebastiano Vigna
 * @since 0.4
 * @deprecated Use the new hashing stuff in Sux4J.
 */

@Deprecated
public class LiterallySignedMinimalPerfectHash extends SignedMinimalPerfectHash {
	private static final long serialVersionUID = 1L;
	/** An array containing the original strings. */
	CharSequence[] signature;


	/** Creates a new literally signed order-preserving minimal perfect hash table 
	 * for the given terms using the given number of weights.
	 *
	 * @param terms some terms to hash; it is assumed that there are
	 * no terms with a common prefix of
	 * <code>weightLength</code> characters.
	 * @param weightLength the number of weights used generating the
	 * intermediate hash functions.
	 * @see MinimalPerfectHash#MinimalPerfectHash(Iterable, int)
	 */
    public LiterallySignedMinimalPerfectHash( final Iterable<? extends CharSequence> terms, final int weightLength ) {
		super( terms, weightLength );
    }

	/** Creates a new literally signed order-preserving minimal perfect hash table for the given
	 * terms, using as many weights as the longest term in the collection.
	 *
	 * @param terms some terms to hash; it is assumed that they do not contain duplicates.
	 * @see MinimalPerfectHash#MinimalPerfectHash(Iterable)
	 *	 
	 */
	public LiterallySignedMinimalPerfectHash( final Iterable<? extends CharSequence> terms ) {
		super( terms );
	}

	/** Creates a new literally signed order-preserving minimal perfect hash table for the given file 
	 * of terms using the given number of weights.
	 *
	 * @param termFile an UTF-8 file containing one term on each line; it is assumed that 
	 * it does not contain terms with a common prefix of
	 * <code>weightLength</code> characters.
	 * @param encoding the encoding of <code>wordFile</code>; if <code>null</code>, it
	 * is assumed to be the platform default encoding.
	 * @param weightLength the number of weights used generating the
	 * intermediate hash functions.
	 * @see MinimalPerfectHash#MinimalPerfectHash(String,String,int)
	 */
	public LiterallySignedMinimalPerfectHash( final String termFile, final String encoding, final int weightLength ) {
		super( termFile, encoding, weightLength );
	}

	/** Creates a new literally signed order-preserving minimal perfect hash table for the given file 
	 * of terms.
	 *
	 * @param termFile an UTF-8 file containing one term on each line; it is assumed that 
	 * it does not contain terms with a common prefix of
	 * <code>weightLength</code> characters.
	 * @param encoding the encoding of <code>wordFile</code>; if <code>null</code>, it
	 * is assumed to be the platform default encoding.
	 * @see MinimalPerfectHash#MinimalPerfectHash(String,String)
	 */
	public LiterallySignedMinimalPerfectHash( final String termFile, final String encoding ) {
		super( termFile, encoding );
	}


	@Override
	public void initSignatures( final Iterable<? extends CharSequence> terms ) {
		int i = 0;
	    signature = new CharSequence[ n ];

	    for ( Iterator<? extends CharSequence> e = terms.iterator(); e.hasNext(); i++ ) signature[ i ] = new MutableString( e.next() );
	}

	@Override
	public boolean checkSignature( final CharSequence word, final int index ) {
		if ( n == 0 ) return false; // Empty maps contain no word
	    return signature[ index ].equals( word );
	}

	public boolean checkSignature( final byte[] a, int off, int len, final int index ) {
		if ( n == 0 ) return false; // Empty maps contain no word
		try {
			return signature[ index ].equals( new String( a, off, len, "ISO-8859-1" ) );
		}
		catch ( UnsupportedEncodingException e ) {
			throw new RuntimeException( e );
		}
	}

    public static void main( final String[] arg ) throws InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException, IOException, JSAPException, ClassNotFoundException {
    	MinimalPerfectHash.main( LiterallySignedMinimalPerfectHash.class, arg );
    }
}