| /* |
| * 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. |
| */ |
| |
| using System; |
| |
| using IndexOutput = Lucene.Net.Store.IndexOutput; |
| using RAMOutputStream = Lucene.Net.Store.RAMOutputStream; |
| |
| namespace Lucene.Net.Index |
| { |
| |
| /// <summary> This abstract class writes skip lists with multiple levels. |
| /// |
| /// Example for skipInterval = 3: |
| /// c (skip level 2) |
| /// c c c (skip level 1) |
| /// x x x x x x x x x x (skip level 0) |
| /// d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d (posting list) |
| /// 3 6 9 12 15 18 21 24 27 30 (df) |
| /// |
| /// d - document |
| /// x - skip data |
| /// c - skip data with child pointer |
| /// |
| /// Skip level i contains every skipInterval-th entry from skip level i-1. |
| /// Therefore the number of entries on level i is: floor(df / ((skipInterval ^ (i + 1))). |
| /// |
| /// Each skip entry on a level i>0 contains a pointer to the corresponding skip entry in list i-1. |
| /// This guarantess a logarithmic amount of skips to find the target document. |
| /// |
| /// While this class takes care of writing the different skip levels, |
| /// subclasses must define the actual format of the skip data. |
| /// |
| /// </summary> |
| abstract class MultiLevelSkipListWriter |
| { |
| // number of levels in this skip list |
| private int numberOfSkipLevels; |
| |
| // the skip interval in the list with level = 0 |
| private int skipInterval; |
| |
| // for every skip level a different buffer is used |
| private RAMOutputStream[] skipBuffer; |
| |
| protected internal MultiLevelSkipListWriter(int skipInterval, int maxSkipLevels, int df) |
| { |
| this.skipInterval = skipInterval; |
| |
| // calculate the maximum number of skip levels for this document frequency |
| numberOfSkipLevels = df == 0?0:(int) System.Math.Floor(System.Math.Log(df) / System.Math.Log(skipInterval)); |
| |
| // make sure it does not exceed maxSkipLevels |
| if (numberOfSkipLevels > maxSkipLevels) |
| { |
| numberOfSkipLevels = maxSkipLevels; |
| } |
| } |
| |
| protected internal virtual void Init() |
| { |
| skipBuffer = new RAMOutputStream[numberOfSkipLevels]; |
| for (int i = 0; i < numberOfSkipLevels; i++) |
| { |
| skipBuffer[i] = new RAMOutputStream(); |
| } |
| } |
| |
| protected internal virtual void ResetSkip() |
| { |
| // creates new buffers or empties the existing ones |
| if (skipBuffer == null) |
| { |
| Init(); |
| } |
| else |
| { |
| for (int i = 0; i < skipBuffer.Length; i++) |
| { |
| skipBuffer[i].Reset(); |
| } |
| } |
| } |
| |
| /// <summary> Subclasses must implement the actual skip data encoding in this method. |
| /// |
| /// </summary> |
| /// <param name="level">the level skip data shall be writting for |
| /// </param> |
| /// <param name="skipBuffer">the skip buffer to write to |
| /// </param> |
| protected internal abstract void WriteSkipData(int level, IndexOutput skipBuffer); |
| |
| /// <summary> Writes the current skip data to the buffers. The current document frequency determines |
| /// the max level is skip data is to be written to. |
| /// |
| /// </summary> |
| /// <param name="df">the current document frequency |
| /// </param> |
| /// <throws> IOException </throws> |
| internal virtual void BufferSkip(int df) |
| { |
| int numLevels; |
| |
| // determine max level |
| for (numLevels = 0; (df % skipInterval) == 0 && numLevels < numberOfSkipLevels; df /= skipInterval) |
| { |
| numLevels++; |
| } |
| |
| long childPointer = 0; |
| |
| for (int level = 0; level < numLevels; level++) |
| { |
| WriteSkipData(level, skipBuffer[level]); |
| |
| long newChildPointer = skipBuffer[level].FilePointer; |
| |
| if (level != 0) |
| { |
| // store child pointers for all levels except the lowest |
| skipBuffer[level].WriteVLong(childPointer); |
| } |
| |
| //remember the childPointer for the next level |
| childPointer = newChildPointer; |
| } |
| } |
| |
| /// <summary> Writes the buffered skip lists to the given output. |
| /// |
| /// </summary> |
| /// <param name="output">the IndexOutput the skip lists shall be written to |
| /// </param> |
| /// <returns> the pointer the skip list starts |
| /// </returns> |
| internal virtual long WriteSkip(IndexOutput output) |
| { |
| long skipPointer = output.FilePointer; |
| if (skipBuffer == null || skipBuffer.Length == 0) |
| return skipPointer; |
| |
| for (int level = numberOfSkipLevels - 1; level > 0; level--) |
| { |
| long length = skipBuffer[level].FilePointer; |
| if (length > 0) |
| { |
| output.WriteVLong(length); |
| skipBuffer[level].WriteTo(output); |
| } |
| } |
| skipBuffer[0].WriteTo(output); |
| |
| return skipPointer; |
| } |
| } |
| } |