codedcharsequencebooleaniterator.java

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

package it.unimi.dsi.mg4j.compression;

/*		 
* MG4J: Managing Gigabytes for Java
*
* Copyright (C) 2005-2007 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 it.unimi.dsi.fastutil.booleans.AbstractBooleanIterator;
import it.unimi.dsi.fastutil.chars.Char2IntMap;

import java.util.NoSuchElementException;

import cern.colt.bitvector.BitVector;


/** A wrapper for character sequences that exposes them as a boolean iterators
 * returning the bits obtained coding the sequence, using
 * a given map from character to symbols in a prefix coder.
 * 
 * <P>This class is very lightweight: it just scans the string, concatenating
 * lazily the bits of each codeword.
 * @deprecated Moved to <code>dsiutils</code>.
 */

@Deprecated
public class CodedCharSequenceBooleanIterator extends AbstractBooleanIterator {
	private final CharSequence s;
	private final int length;
	private final Char2IntMap char2code;
	private final BitVector[] codeWord;
	
	private BitVector char2codeWord( final char c ) {
		return codeWord[ char2code.get( c ) ];
	}
	
	private int pos, index;
	private BitVector currCodeWord;
	
	/** Creates a new boolean iterator over a character sequence. 
	 * 
	 * @param s a character sequence.
	 * @param prefixCoder a prefix coder that is able to code the characters in <code>s</code>, or possibly <code>null</code> if
	 * <code>s</code> is empty.
	 * @param char2code the map from characters in <code>s</code> to symbols in <code>coder</code>.
	 */
	
	public CodedCharSequenceBooleanIterator( final CharSequence s, final PrefixCoder prefixCoder, final Char2IntMap char2code ) {
		this.s = s;
		this.char2code = char2code;
		this.length = s.length();
		if ( s.length() > 0 && prefixCoder == null ) throw new IllegalArgumentException( "Empty PrefixCoder with non empty string: " + s );
		this.codeWord = prefixCoder != null ? prefixCoder.codeWords() : null;
		if ( length != 0 ) currCodeWord = char2codeWord( s.charAt( 0 ) ); 
	}

	public boolean hasNext() {
		/* If the current codeword has lenth 0, there's nothing to code. Note that
		 * in this case by definition the current codeword is also the *only* codeword. */
		return currCodeWord.size() > 0 && pos < length;
	}

	public boolean nextBoolean() {
		if ( ! hasNext() ) throw new NoSuchElementException();
		final boolean bit = currCodeWord.get( index++ );
		if ( index == currCodeWord.size() ) {
			pos++;
			if ( pos < length ) {
				currCodeWord = char2codeWord( s.charAt( pos ) );
				index = 0;
			}
		}
		return bit;
	}
}