address a few more comments on roaring

processing/src/main/java/io/druid/segment/IndexIO.java

@@ -756,6 +756,10 @@ public class IndexIO
       SmooshedFileMapper smooshedFiles = Smoosh.map(inDir);
 
       ByteBuffer indexBuffer = smooshedFiles.mapFile("index.drd");
+      /**
+       * Index.drd should consist of the segment version, the columns and dimensions of the segment as generic
+       * indexes, the interval start and end millis as longs (in 16 bytes), and a bitmap index type.
+       */
       final GenericIndexed<String> cols = GenericIndexed.read(indexBuffer, GenericIndexed.stringStrategy);
       final GenericIndexed<String> dims = GenericIndexed.read(indexBuffer, GenericIndexed.stringStrategy);
       final Interval dataInterval = new Interval(indexBuffer.getLong(), indexBuffer.getLong());
@@ -768,7 +772,7 @@ public class IndexIO
       if (indexBuffer.hasRemaining()) {
         segmentBitmapSerdeFactory = mapper.readValue(serializerUtils.readString(indexBuffer), BitmapSerdeFactory.class);
       } else {
-        segmentBitmapSerdeFactory = BitmapSerdeFactory.DEFAULT_BITMAP_SERDE_FACTORY;
+        segmentBitmapSerdeFactory = new ConciseBitmapSerdeFactory();
       }
 
       Map<String, Column> columns = Maps.newHashMap();

processing/src/main/java/io/druid/segment/data/BitmapSerdeFactory.java

@@ -34,8 +34,6 @@ import com.metamx.collections.bitmap.ImmutableBitmap;
 
 public interface BitmapSerdeFactory
 {
-  public static BitmapSerdeFactory DEFAULT_BITMAP_SERDE_FACTORY = new ConciseBitmapSerdeFactory();
-
   public ObjectStrategy<ImmutableBitmap> getObjectStrategy();
 
   public BitmapFactory getBitmapFactory();

processing/src/main/java/io/druid/segment/data/ConciseCompressedIndexedInts.java

@@ -26,7 +26,6 @@ import com.metamx.common.ISE;
 import it.uniroma3.mat.extendedset.intset.ImmutableConciseSet;
 import it.uniroma3.mat.extendedset.intset.IntSet;
 
-import javax.annotation.Nullable;
 import java.nio.ByteBuffer;
 import java.util.Iterator;
 
@@ -65,11 +64,10 @@ public class ConciseCompressedIndexedInts implements IndexedInts, Comparable<Imm
   }
 
   @Override
-  public int compareTo(@Nullable ImmutableBitmap conciseCompressedIndexedInts)
+  public int compareTo(ImmutableBitmap conciseCompressedIndexedInts)
   {
-    // TODO
     if (!(conciseCompressedIndexedInts instanceof WrappedImmutableConciseBitmap)) {
-      throw new ISE("WTF bro! No, bad.");
+      throw new ISE("Unknown class [%s]", conciseCompressedIndexedInts.getClass());
     }
 
     return immutableConciseSet.compareTo(((WrappedImmutableConciseBitmap) conciseCompressedIndexedInts).getBitmap());

processing/src/main/java/io/druid/segment/serde/DictionaryEncodedColumnPartSerde.java

@@ -30,6 +30,7 @@ import io.druid.segment.column.ColumnConfig;
 import io.druid.segment.column.ValueType;
 import io.druid.segment.data.BitmapSerdeFactory;
 import io.druid.segment.data.ByteBufferSerializer;
+import io.druid.segment.data.ConciseBitmapSerdeFactory;
 import io.druid.segment.data.GenericIndexed;
 import io.druid.segment.data.IndexedRTree;
 import io.druid.segment.data.VSizeIndexed;
@@ -96,7 +97,7 @@ public class DictionaryEncodedColumnPartSerde implements ColumnPartSerde
   {
     this.isSingleValued = isSingleValued;
     this.bitmapSerdeFactory = bitmapSerdeFactory == null
-                              ? BitmapSerdeFactory.DEFAULT_BITMAP_SERDE_FACTORY
+                              ? new ConciseBitmapSerdeFactory()
                               : bitmapSerdeFactory;
 
     this.dictionary = null;