presto-main/src/main/java/io/prestosql/type/DecimalParametricType.java/DecimalParametricType/createType
class DecimalParametricType:    @Override
    public Type createType(TypeManager typeManager, List<TypeParameter> parameters)
    {
        switch (parameters.size()) {
            case 0:
                return DecimalType.createDecimalType();
            case 1:
                return DecimalType.createDecimalType(parameters.get(0).getLongLiteral().intValue());
            case 2:
                return DecimalType.createDecimalType(parameters.get(0).getLongLiteral().intValue(), parameters.get(1).getLongLiteral().intValue());
            default:
                throw new IllegalArgumentException("Expected 0, 1 or 2 parameters for DECIMAL type constructor.");
        }
    }