@Override
  public void evaluate(VectorizedRowBatch batch) throws HiveException {

    if (childExpressions != null) {
      this.evaluateChildren(batch);
    }

    ColumnVector inputColVector = batch.cols[inputColumnNum[0]];
    BytesColumnVector outputColVector = (BytesColumnVector) batch.cols[outputColumnNum];

    int[] sel = batch.selected;
    boolean[] inputIsNull = inputColVector.isNull;
    boolean[] outputIsNull = outputColVector.isNull;
    int n = batch.size;

    // return immediately if batch is empty
    if (n == 0) {
      return;
    }

    // We do not need to do a column reset since we are carefully changing the output.
    outputColVector.isRepeating = false;

    if (inputColVector.isRepeating) {
      if (inputColVector.noNulls || !inputIsNull[0]) {
        outputIsNull[0] = false;
        truncDate(inputColVector, outputColVector, 0);
      } else {
        outputIsNull[0] = true;
        outputColVector.noNulls = false;
      }
      outputColVector.isRepeating = true;
      return;
    }

    if (inputColVector.noNulls) {
      if (batch.selectedInUse) {

        // CONSIDER: For large n, fill n or all of isNull array and use the tighter ELSE loop.
        if (!outputColVector.noNulls) {
          for (int j = 0; j != n; j++) {
            final int i = sel[j];
            // Set isNull before call in case it changes it mind.
            outputIsNull[i] = false;
            truncDate(inputColVector, outputColVector, i);
          }
        } else {
          for (int j = 0; j != n; j++) {
            final int i = sel[j];
            truncDate(inputColVector, outputColVector, i);
          }
        }
      } else {
        if (!outputColVector.noNulls) {

          // Assume it is almost always a performance win to fill all of isNull so we can
          // safely reset noNulls.
          Arrays.fill(outputIsNull, false);
          outputColVector.noNulls = true;
        }
        for (int i = 0; i != n; i++) {
          truncDate(inputColVector, outputColVector, i);
        }
      }
    } else /* there are nulls in the inputColVector */ {

      // Carefully handle NULLs...
      outputColVector.noNulls = false;

      if (batch.selectedInUse) {
        for (int j = 0; j != n; j++) {
          int i = sel[j];
          outputIsNull[i] = inputIsNull[i];
          if (!inputIsNull[i]) {
            truncDate(inputColVector, outputColVector, i);
          }
        }
      } else {
        System.arraycopy(inputIsNull, 0, outputIsNull, 0, n);
        for (int i = 0; i != n; i++) {
          if (!inputColVector.isNull[i]) {
            truncDate(inputColVector, outputColVector, i);
          }
        }
      }
    }
  }
Vectorized implementation of trunc(date, fmt) function for timestamp input
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/TruncDateFromTimestamp.java