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.vector;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.FloatBuffer;
  import java.nio.IntBuffer;
  
  import com.google.common.primitives.Ints;
  
  import io.github.jbellis.jvector.disk.ReaderSupplier;
  import org.apache.cassandra.io.util.FileHandle;
  import org.apache.cassandra.io.util.RandomAccessReader;
  import org.apache.cassandra.io.util.Rebufferer.BufferHolder;
  
  public class RandomAccessReaderAdapter extends RandomAccessReader implements io.github.jbellis.jvector.disk.RandomAccessReader
  {
      static ReaderSupplier createSupplier(FileHandle fileHandle)
      {
          return () -> new RandomAccessReaderAdapter(fileHandle);
      }
  
      RandomAccessReaderAdapter(FileHandle fileHandle)
      {
          super(fileHandle.instantiateRebufferer(null));
      }
  
      @Override
      public void readFully(float[] dest) throws IOException
      {
          BufferHolder bh = bufferHolder;
          long position = getPosition();
  
          FloatBuffer floatBuffer;
          if (bh.offset() == 0 && position % Float.BYTES == 0)
          {
              // this is a separate code path because buffer() and asFloatBuffer() both allocate
              // new and relatively expensive xBuffer objects, so we want to avoid doing that
              // twice, where possible
              floatBuffer = bh.floatBuffer();
              floatBuffer.position(Ints.checkedCast(position / Float.BYTES));
          }
          else
          {
              // offset is non-zero, and probably not aligned to Float.BYTES, so
              // set the position before converting to FloatBuffer.
              ByteBuffer bb = bh.buffer();
              bb.position(Ints.checkedCast(position - bh.offset()));
              floatBuffer = bb.asFloatBuffer();
          }
  
          if (dest.length > floatBuffer.remaining())
          {
              // slow path -- desired slice is across region boundaries
              ByteBuffer bb = ByteBuffer.allocate(Float.BYTES * dest.length);
              readFully(bb);
              floatBuffer = bb.asFloatBuffer();
          }
  
          floatBuffer.get(dest);
          seek(position + (long) Float.BYTES * dest.length);
      }
  
      /**
       * Read ints into an int[], starting at the current position.
       *
       * @param dest the array to read into
       * @param offset the offset in the array at which to start writing ints
       * @param count the number of ints to read
       *
       * Will change the buffer position.
       */
      @Override
      public void read(int[] dest, int offset, int count) throws IOException
      {
          if (count == 0)
              return;
  
          BufferHolder bh = bufferHolder;
          long position = getPosition();
  
          IntBuffer intBuffer;
          if (bh.offset() == 0 && position % Integer.BYTES == 0)
          {
              // this is a separate code path because buffer() and asIntBuffer() both allocate
              // new and relatively expensive xBuffer objects, so we want to avoid doing that
              // twice, where possible
              intBuffer = bh.intBuffer();
              intBuffer.position(Ints.checkedCast(position / Integer.BYTES));
          }
          else
          {
              // offset is non-zero, and probably not aligned to Integer.BYTES, so
              // set the position before converting to IntBuffer.
              ByteBuffer bb = bh.buffer();
              bb.position(Ints.checkedCast(position - bh.offset()));
              intBuffer = bb.asIntBuffer();
          }
  
          if (count > intBuffer.remaining())
          {
              // slow path -- desired slice is across region boundaries
              ByteBuffer bb = ByteBuffer.allocate(Integer.BYTES * count);
              readFully(bb);
              intBuffer = bb.asIntBuffer();
          }
  
          intBuffer.get(dest, offset, count);
          seek(position + (long) Integer.BYTES * count);
      }
  }
  