content: /*
   * 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.cassandra.index.sai.disk.v1.bitpack;
  
  import java.io.IOException;
  
  import org.apache.lucene.store.IndexOutput;
  import org.apache.lucene.util.packed.DirectWriter;
  
  import static org.apache.lucene.util.BitUtil.zigZagEncode;
  
  /**
   * A writer for large sequences of longs.
   *
   * Modified copy of {@link org.apache.lucene.util.packed.BlockPackedWriter} to use {@link DirectWriter}
   * for optimised reads that doesn't require seeking through the whole file to open a thread-exclusive reader.
   */
  public class BlockPackedWriter extends AbstractBlockPackedWriter
  {
      static final int BPV_SHIFT = 1;
      static final int MIN_VALUE_EQUALS_0 = 1;
  
      public BlockPackedWriter(IndexOutput out, int blockSize)
      {
          super(out, blockSize);
      }
  
      @Override
      protected void flushBlock() throws IOException
      {
          long min = Long.MAX_VALUE, max = Long.MIN_VALUE;
          for (int i = 0; i < blockIndex; ++i)
          {
              min = Math.min(blockValues[i], min);
              max = Math.max(blockValues[i], max);
          }
  
          long delta = max - min;
          int bitsRequired = delta == 0 ? 0 : DirectWriter.unsignedBitsRequired(delta);
  
          int shiftedBitsRequired = (bitsRequired << BPV_SHIFT) | (min == 0 ? MIN_VALUE_EQUALS_0 : 0);
          blockMetaWriter.writeByte((byte) shiftedBitsRequired);
  
          if (min != 0)
          {
              writeVLong(blockMetaWriter, zigZagEncode(min) - 1);
          }
  
          if (bitsRequired > 0)
          {
              if (min != 0)
              {
                  for (int i = 0; i < blockIndex; ++i)
                  {
                      blockValues[i] -= min;
                  }
              }
              blockMetaWriter.writeVLong(indexOutput.getFilePointer());
              writeValues(blockIndex, bitsRequired);
          }
      }
  }
  