| /* |
| * 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); |
| } |
| } |