private void transformLong(Row row) throws IOException {
    long v = row.getLong(0);
    longMin = Math.min(longMin, v);
    longMax = Math.max(longMax, v);
  }
This function is used to calculate the spread of time series, that is, the maximum value minus
the minimum value.
library-udf/src/main/java/org/apache/iotdb/library/dprofile/UDAFSpread.java