public BigInteger split2(BigInteger a, BigInteger b) {
      return a.add(b).divide(BigInteger.valueOf(2)).abs();
    }
Divide 2 numbers in half (for split algorithm)
@param a number #1
@param b number #2
@return the midpoint of the 2 numbers
hbase-server/src/main/java/org/apache/hadoop/hbase/util/RegionSplitter.java