/*
* 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 org.apache.solr.util.hll;
/**
* A collection of test utilities for constructing input values to HLLs and for
* computing their serialized size.
*/
public class ProbabilisticTestUtil {
/**
* Constructs a value that when added raw to a HLL will set the register at
* <code>registerIndex</code> to <code>registerValue</code>.
*
* @param log2m the log-base-2 of the number of registers in the HLL
* @param registerIndex the index of the register to set
* @param registerValue the value to set the register to
* @return the value
*/
public static long constructHLLValue(final int log2m, final int registerIndex, final int registerValue) {
final long partition = registerIndex;
final long substreamValue = (1L << (registerValue - 1));
return (substreamValue << log2m) | partition;
}
/**
* Extracts the HLL register index from a raw value.
*/
public static short getRegisterIndex(final long rawValue, final int log2m) {
final long mBitsMask = (1 << log2m) - 1;
final short j = (short)(rawValue & mBitsMask);
return j;
}
/**
* Extracts the HLL register value from a raw value.
*/
public static byte getRegisterValue(final long rawValue, final int log2m) {
final long substreamValue = (rawValue >>> log2m);
final byte p_w;
if (substreamValue == 0L) {
// The paper does not cover p(0x0), so the special value 0 is used.
// 0 is the original initialization value of the registers, so by
// doing this the HLL simply ignores it. This is acceptable
// because the probability is 1/(2^(2^registerSizeInBits)).
p_w = 0;
} else {
p_w = (byte)Math.min(1 + BitUtil.leastSignificantBit(substreamValue), 31);
}
return p_w;
}
/**
* @return the number of bytes required to pack <code>registerCount</code>
* registers of width <code>shortWordLength</code>.
*/
public static int getRequiredBytes(final int shortWordLength, final int registerCount) {
return (int)Math.ceil((registerCount * shortWordLength)/(float)8);
}
}