code: public Chunk chunkFor(long position) {
          // position of the chunk
          int idx = 8 * (int) (position / parameters.chunkLength());
  
          if (idx >= chunkOffsets.size())
              throw new CorruptSSTableException(new EOFException(), indexFilePath);
  
          long chunkOffset = chunkOffsets.getLong(idx);
          long nextChunkOffset = (idx + 8 == chunkOffsets.size())
                  ? compressedFileLength
                  : chunkOffsets.getLong(idx + 8);
  
          return new Chunk(chunkOffset, (int) (nextChunkOffset - chunkOffset - 4)); // "4" bytes reserved for checksum
      }
docs: Get a chunk of compressed data (offset, length) corresponding to given position
  
  @param position Position in the file.
  @return pair of chunk offset and length.