[v1_enum] enum {...}
typedef [v1_enum] enum {label1, label2, ...};
Remarks
The v1_enum attribute directs that the specified enumerated type be transmitted as a 32-bit entity, rather than the 16-bit default. This increases the efficiency of marshalling and unmarshalling data when such an enumerator is embedded in structures or unions.
For improved performance, we recommend applying the v1_enum attribute to enumerators in 32-bit applications. Keep in mind, however, that on 16-bit platforms the C compiler treats an enumerated type as a 16-bit int. Therefore 16-bit client applications need to convert enum types to long for remote transmission in order to avoid overwriting data or sending incorrect values.