hyracks-storage-am-invertedindex/src/main/java/edu/uci/ics/hyracks/storage/am/invertedindex/tokenizers/HashedUTF8NGramToken.java

/**
 * Copyright 2010-2011 The Regents of the University of California
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on
 * an "AS IS"; BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations under
 * the License.
 * 
 * Author: Alexander Behm <abehm (at) ics.uci.edu>
 */

package edu.uci.ics.hyracks.storage.am.invertedindex.tokenizers;

import java.io.DataOutput;
import java.io.IOException;

import edu.uci.ics.hyracks.dataflow.common.data.util.StringUtils;

public class HashedUTF8NGramToken extends UTF8NGramToken {
	public HashedUTF8NGramToken(byte tokenTypeTag, byte countTypeTag) {
		super(tokenTypeTag, countTypeTag);
	}

	@Override
	public void serializeToken(DataOutput dos) throws IOException {
		handleTokenTypeTag(dos);

		int hash = GOLDEN_RATIO_32;

		// pre chars
		for (int i = 0; i < numPreChars; i++) {
			hash ^= PRECHAR;
			hash *= GOLDEN_RATIO_32;
		}

		// regular chars
		int numRegGrams = tokenLength - numPreChars - numPostChars;
		int pos = start;
		for (int i = 0; i < numRegGrams; i++) {
			hash ^= StringUtils.toLowerCase(StringUtils.charAt(data, pos));
			hash *= GOLDEN_RATIO_32;
			pos += StringUtils.charSize(data, pos);
		}

		// post chars
		for (int i = 0; i < numPostChars; i++) {
			hash ^= POSTCHAR;
			hash *= GOLDEN_RATIO_32;
		}

		// token count
		hash += tokenCount;

		dos.writeInt(hash);
	}
}