public static long extractPartialHashCode(long hashCode) {
    return (hashCode >>> KeyRef.PartialHashCode.intChooseBitShift) & KeyRef.PartialHashCode.bitMask;
  }
Extract partial hash code from the full hash code.

Choose the high bits of the hash code KNOWING it was calculated as an int.

We want the partial hash code to be different than the
lower bits used for our hash table slot calculations.

@param hashCode
@return
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/mapjoin/fast/VectorMapJoinFastBytesHashKeyRef.java