static int getCommonLength(int aLen, int bLen) {
    int maxLength;
    if (aLen < 0 || bLen < 0) {
      // negative length should take precedence over positive value?
      maxLength = -1;
    } else {
      maxLength = Math.max(aLen, bLen);
    }
    return maxLength;
  }
Check if a type is exact (not approximate such as float and double). String is considered as
double, thus not exact.

@param typeInfo
@return
ql/src/java/org/apache/hadoop/hive/ql/exec/FunctionRegistry.java