| /* |
| * 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.datasketches; |
| |
| /** |
| * This is a special power law updating scheme that has the following properties: |
| * <ul><li>The grand total weight of all updates is a power of 2.</li> |
| * <li>The total weight of each row of updates at a specific weight is a power of 2.</li> |
| * <li>Each specific weighted update has a weight that is a power of 2.</li> |
| * <li>The number of update rows is a power of 2.</li> |
| *</ul> |
| * |
| * <p>There are 5 schemes and you implement only one of these schemes:</p> |
| * <table> |
| * <caption><big><b>Scheme Details</b></big></caption> |
| * <tbody> |
| * <tr> |
| * <td> <b>Scheme</b></td> |
| * <td><b>WeightPerRow</b> </td> |
| * <td><b>NumRows</b> </td> |
| * <td><b>TotalSchemeWeight</b> </td> |
| * </tr> |
| * <tr> |
| * <td> 1</td> |
| * <td> 2</td> |
| * <td> 2</td> |
| * <td> 4</td> |
| * </tr> |
| * <tr> |
| * <td> 2</td> |
| * <td> 8</td> |
| * <td> 4</td> |
| * <td> 32</td> |
| * </tr> |
| * <tr> |
| * <td> 3</td> |
| * <td> 128</td> |
| * <td> 8</td> |
| * <td> 1,024</td> |
| * </tr> |
| * <tr> |
| * <td> 4</td> |
| * <td> 32,768</td> |
| * <td> 16</td> |
| * <td> 524,288</td> |
| * </tr> |
| * <tr> |
| * <td> 5</td> |
| * <td> 2,147,483,648</td> |
| * <td> 32</td> |
| * <td> 68,719,476,736</td> |
| * </tr> |
| * </tbody> |
| * </table> |
| * |
| * @author Lee Rhodes |
| */ |
| public final class PowersOf2PowerLaw { |
| //s or scheme is Scheme number |
| //m is Log2(Row Weight) = 2^s -1 |
| //w is Row Weight = 2^m |
| //r is Num Rows = 2^s |
| //sw is Scheme Weight = 2^(m + s) |
| |
| /** |
| * Gets the total weight of each row. |
| * @param scheme the given scheme, 1 to 5. |
| * @return the total weight of each row. |
| */ |
| public static long getTotalRowWeight(final int scheme) { |
| checkScheme(scheme); |
| final long m = (1L << scheme) - 1L; |
| return 1L << m; |
| } |
| |
| /** |
| * Gets the total Scheme Weight for all rows with their weights and repetitions. |
| * @param scheme the given scheme, 1 to 5. |
| * @return the total Scheme Weight for all rows with their weights and repetitions. |
| */ |
| public static long getTotalSchemeWeight(final int scheme) { |
| checkScheme(scheme); |
| final long m = (1L << scheme) - 1L; |
| return 1L << (m + scheme); |
| } |
| |
| /** |
| * Gets the number of rows for a given scheme. |
| * @param scheme the given scheme, 1 to 5. |
| * @return the number of rows for a given scheme. |
| */ |
| public static int getNumRows(final int scheme) { |
| checkScheme(scheme); |
| return 1 << scheme; |
| } |
| |
| /** |
| * Gets the weight of each update for the given row. |
| * @param row starting with zero, which has a weight of 1, row 1 has a weight of 2, |
| * row n has a weight of 2^n. |
| * @return the weight of updates for the given row. |
| */ |
| public static long getRowWeight(final int row) { |
| return 1L << row; |
| } |
| |
| /** |
| * Gets the number of repetitions for a given scheme and row. |
| * @param scheme the given scheme, 1 to 5. |
| * @param row starting with zero, which has a weight of 1, row 1 has a weight of 2, |
| * row n has a weight of 2^n. |
| * @return the number of repetitions for a given scheme and row. |
| */ |
| public static long getRowReps(final int scheme, final int row) { |
| checkScheme(scheme); |
| final long rw = getTotalRowWeight(scheme); |
| return rw >>> row; |
| } |
| |
| private static void checkScheme(final int scheme) { |
| if (scheme < 1 || scheme > 5) { |
| throw new IllegalArgumentException("Scheme must be >= 1 and <= 5."); |
| } |
| } |
| |
| } |
