private int pageIndex(long pointer) {
    return (int)
        ((pointer
                & (SchemaFileConfig.PAGE_INDEX_MASK << SchemaFileConfig.COMP_POINTER_OFFSET_DIGIT))
            >> SchemaFileConfig.COMP_POINTER_OFFSET_DIGIT);
  }
CompoundPointer structure (from high bits to low):

<ul>
  <li>16 bits: reserved
  <li>32 bits: page index, which points to target content
  <li>16 bits: key offset, which denotes where key is in this page/segment.
</ul>
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/schemafile/InternalPage.java