@Override
  public Descriptor getDescriptor() {
    VectorExpressionDescriptor.Builder b = new VectorExpressionDescriptor.Builder();
    b.setMode(VectorExpressionDescriptor.Mode.PROJECTION).setNumArguments(2)
        .setArgumentTypes(getInputColumnType(), VectorExpressionDescriptor.ArgumentType.INT_FAMILY)
        .setInputExpressionTypes(VectorExpressionDescriptor.InputExpressionType.COLUMN,
            VectorExpressionDescriptor.InputExpressionType.SCALAR);
    return b.build();
  }
Vectorized implementation of trunc(number, scale) function for float/double input
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/TruncFloat.java