http://lucene.apache.org/lucene-parent/lucene-backward-codecs: Codecs for older versions of Lucene. (The Apache Software Foundation) 
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package org.apache.lucene.codecs.lucene70;

import java.io.IOException;

import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.NormsConsumer;
import org.apache.lucene.codecs.NormsFormat;
import org.apache.lucene.codecs.NormsProducer;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.store.DataOutput;


Lucene 7.0 Score normalization format.


Encodes normalization values by encoding each value with the minimum
number of bytes needed to represent the range (which can be zero).


Files:

    
  
  1. .nvd: Norms data
    2. 
  
  2. .nvm: Norms metadata
    3. 



    
  
  1. 
  
    The Norms metadata or .nvm file.
    
  
    For each norms field, this stores metadata, such as the offset into the 
     Norms data (.nvd)
    
  
    Norms metadata (.dvm) --> Header,<Entry>NumFields,Footer
    
  
      
    
    • Header --> IndexHeader
      • 
    
    • Entry --> FieldNumber, DocsWithFieldAddress, DocsWithFieldLength, NumDocsWithField, BytesPerNorm, NormsAddress
      • 
    
    • FieldNumber --> Int32
      • 
    
    • DocsWithFieldAddress --> Int64
      • 
    
    • DocsWithFieldLength --> Int64
      • 
    
    • NumDocsWithField --> Int32
      • 
    
    • BytesPerNorm --> byte
      • 
    
    • NormsAddress --> Int64
      • 
    
    • Footer --> CodecFooter
      • 
  
    
  
    FieldNumber of -1 indicates the end of metadata.
    
  
    NormsAddress is the pointer to the start of the data in the norms data (.nvd), or the singleton value 
     when BytesPerValue = 0. If BytesPerValue is different from 0 then there are NumDocsWithField values
     to read at that offset.
    
  
    DocsWithFieldAddress is the pointer to the start of the bit set containing documents that have a norm
     in the norms data (.nvd), or -2 if no documents have a norm value, or -1 if all documents have a norm
     value.
    
  
    DocsWithFieldLength is the number of bytes used to encode the set of documents that have a norm.
    
  
  2. 
  
    The Norms data or .nvd file.
    
  
    For each Norms field, this stores the actual per-document data (the heavy-lifting)
    
  
    Norms data (.nvd) --> Header,< Data >NumFields,Footer
    
  
      
    
    • Header --> IndexHeader
      • 
    
    • DocsWithFieldData --> Bit set of MaxDoc bits
      • 
    
    • NormsData --> byteNumDocsWithField * BytesPerValue
      • 
    
    • Footer --> CodecFooter
      • 
  
    



@lucene.experimental
/**
 * Lucene 7.0 Score normalization format.
 * <p>
 * Encodes normalization values by encoding each value with the minimum
 * number of bytes needed to represent the range (which can be zero).
 * <p>
 * Files:
 * <ol>
 *   <li><tt>.nvd</tt>: Norms data</li>
 *   <li><tt>.nvm</tt>: Norms metadata</li>
 * </ol>
 * <ol>
 *   <li><a name="nvm"></a>
 *   <p>The Norms metadata or .nvm file.</p>
 *   <p>For each norms field, this stores metadata, such as the offset into the 
 *      Norms data (.nvd)</p>
 *   <p>Norms metadata (.dvm) --&gt; Header,&lt;Entry&gt;<sup>NumFields</sup>,Footer</p>
 *   <ul>
 *     <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}</li>
 *     <li>Entry --&gt; FieldNumber, DocsWithFieldAddress, DocsWithFieldLength, NumDocsWithField, BytesPerNorm, NormsAddress</li>
 *     <li>FieldNumber --&gt; {@link DataOutput#writeInt Int32}</li>
 *     <li>DocsWithFieldAddress --&gt; {@link DataOutput#writeLong Int64}</li>
 *     <li>DocsWithFieldLength --&gt; {@link DataOutput#writeLong Int64}</li>
 *     <li>NumDocsWithField --&gt; {@link DataOutput#writeInt Int32}</li>
 *     <li>BytesPerNorm --&gt; {@link DataOutput#writeByte byte}</li>
 *     <li>NormsAddress --&gt; {@link DataOutput#writeLong Int64}</li>
 *     <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}</li>
 *   </ul>
 *   <p>FieldNumber of -1 indicates the end of metadata.</p>
 *   <p>NormsAddress is the pointer to the start of the data in the norms data (.nvd), or the singleton value 
 *      when BytesPerValue = 0. If BytesPerValue is different from 0 then there are NumDocsWithField values
 *      to read at that offset.</p>
 *   <p>DocsWithFieldAddress is the pointer to the start of the bit set containing documents that have a norm
 *      in the norms data (.nvd), or -2 if no documents have a norm value, or -1 if all documents have a norm
 *      value.</p>
 *   <p>DocsWithFieldLength is the number of bytes used to encode the set of documents that have a norm.</p>
 *   <li><a name="nvd"></a>
 *   <p>The Norms data or .nvd file.</p>
 *   <p>For each Norms field, this stores the actual per-document data (the heavy-lifting)</p>
 *   <p>Norms data (.nvd) --&gt; Header,&lt; Data &gt;<sup>NumFields</sup>,Footer</p>
 *   <ul>
 *     <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}</li>
 *     <li>DocsWithFieldData --&gt; Bit set of MaxDoc bits</li>
 *     <li>NormsData --&gt; {@link DataOutput#writeByte(byte) byte}<sup>NumDocsWithField * BytesPerValue</sup></li>
 *     <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}</li>
 *   </ul>
 * </ol>
 * @lucene.experimental
 */
public class Lucene70NormsFormat extends NormsFormat {

  
Sole Constructor 
/** Sole Constructor */
  public Lucene70NormsFormat() {}
  
  @Override
  public NormsConsumer normsConsumer(SegmentWriteState state) throws IOException {
    return new Lucene70NormsConsumer(state, DATA_CODEC, DATA_EXTENSION, METADATA_CODEC, METADATA_EXTENSION);
  }

  @Override
  public NormsProducer normsProducer(SegmentReadState state) throws IOException {
    return new Lucene70NormsProducer(state, DATA_CODEC, DATA_EXTENSION, METADATA_CODEC, METADATA_EXTENSION);
  }
  
  private static final String DATA_CODEC = "Lucene70NormsData";
  private static final String DATA_EXTENSION = "nvd";
  private static final String METADATA_CODEC = "Lucene70NormsMetadata";
  private static final String METADATA_EXTENSION = "nvm";
  static final int VERSION_START = 0;
  static final int VERSION_CURRENT = VERSION_START;
}