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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */
package hivemall.knn.distance;

import static hivemall.utils.hadoop.WritableUtils.val;

import java.math.BigInteger;
import java.util.List;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.ql.udf.UDFType;
import org.apache.hadoop.io.IntWritable;

//@formatter:off
@Description(name = "popcnt", value = "_FUNC_(a [, b]) - Returns a popcount value", 
             extended = "select \n" + 
                     "  popcnt(3),\n" + 
                     "  popcnt(\"3\"),  -- 3=0x11\n" + 
                     "  popcnt(array(1,3));\n" + 
                     "\n" + 
                     "2       2       3")
@UDFType(deterministic = true, stateful = false)
//@formatter:on
public final class PopcountUDF extends UDF {

    public IntWritable evaluate(long a) {
        return val(Long.bitCount(a));
    }

    public IntWritable evaluate(String a) {
        BigInteger ai = new BigInteger(a);
        return val(ai.bitCount());
    }

    public IntWritable evaluate(List a) {
        int result = 0;
        for (int i = 0; i < a.size(); i++) {
            long x = a.get(i).longValue();
            result += Long.bitCount(x);
        }
        return val(result);
    }

    /**
     * Count bits that both bits are 1.
     */
    public IntWritable evaluate(long a, long b) {
        long innerProduct = a & b;
        return val(Long.bitCount(innerProduct));
    }

    /**
     * Count bits that both bits are 1.
     */
    public IntWritable evaluate(String a, String b) {
        BigInteger ai = new BigInteger(a);
        BigInteger bi = new BigInteger(b);
        BigInteger innerProduct = ai.and(bi);
        return val(innerProduct.bitCount());
    }

    /**
     * Count bits that both bits are 1.
     */
    public IntWritable evaluate(List a, List b) {
        final int min = Math.min(a.size(), b.size());
        int result = 0;
        for (int i = 0; i < min; i++) {
            long innerProduct = a.get(i).longValue() & b.get(i).longValue();
            result += Long.bitCount(innerProduct);
        }
        return val(result);
    }

}