@Override
  public String vectorExpressionParameters() {
    DecimalTypeInfo decimalTypeInfo1 = (DecimalTypeInfo) inputTypeInfos[1];
    HiveDecimalWritable writable1 = new HiveDecimalWritable();
    writable1.deserialize64(arg2Scalar, decimalTypeInfo1.scale());

    DecimalTypeInfo decimalTypeInfo2 = (DecimalTypeInfo) inputTypeInfos[2];
    HiveDecimalWritable writable2 = new HiveDecimalWritable();
    writable2.deserialize64(arg3Scalar, decimalTypeInfo2.scale());
    return
        getColumnParamString(0, inputColumnNum[0]) +
        ", decimal64Val1 " + arg2Scalar + ", decimalVal1 " + writable1.toString() +
        ", decimal64Val2 " + arg3Scalar + ", decimalVal2 " + writable2.toString();
  }
Compute IF(expr1, expr2, expr3) for 3 input  expressions.
The first is always a boolean (LongColumnVector).
The second is a constant value.
The third is a constant value.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/IfExprDecimal64ScalarDecimal64Scalar.java