public static void NaNToNull(DoubleColumnVector v, int[] sel, boolean selectedInUse, int n) {
    NaNToNull(v, sel, selectedInUse, n, false);
  }
Math expression evaluation helper functions.
Some of these are referenced from ColumnUnaryFunc.txt.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/MathExpr.java