public void sumValueNoCheck(long value) {
      if (Math.abs(sum) > nearDecimal64Max) {
        if (!usingRegularDecimal) {
          usingRegularDecimal = true;
          regularDecimalSum.deserialize64(sum, inputScale);
        } else {
          temp.deserialize64(sum, inputScale);
          regularDecimalSum.mutateAdd(temp);
        }
        sum = value;
      } else {
        sum += value;
      }
    }
Value is explicitly (re)initialized in reset()
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/aggregates/VectorUDAFSumDecimal64ToDecimal.java