@Override
  public Descriptor getDescriptor() {
    VectorExpressionDescriptor.Builder b = new VectorExpressionDescriptor.Builder();
    b.setMode(VectorExpressionDescriptor.Mode.PROJECTION).setNumArguments(1)
        .setArgumentTypes(getInputColumnType())
        .setInputExpressionTypes(VectorExpressionDescriptor.InputExpressionType.COLUMN);
    return b.build();
  }
Vectorized implementation of trunc(number) function for decimal input
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/TruncDecimalNoScale.java