MATLAB: Enums in Bitfields [Greenhills PowerPC Compiler for C]

cgreenhillspolyspacePolyspace Code ProverPolyspace Code Prover Serverpowerpc

I have an enum
    typedef enum
    {
        YES  = 0u,
        NO = 1u
    } AnswerType;
Which is used as a bit field element in a struct
    typedef struct
    {
        uint8_t    messageField;
        uint8_t    padding : 7;
        AnswerType answer  : 1;
    } MessageType;
When attempting to access this field, Polyspace is confusing the enum to be a signed 1 bit bitfield with a range of [-1..0], when in fact it's unsigned [0..1]. This of course causes a chain of errors due to incorrect range values.
Forcing the "auto-unsigned-first" option in Polyspace for "-enum-type-definition" will treat this enum as a u8, however it's actually compiled as u32, thus causing problems in other areas of the analysis (where we rely on it being a u32).
Is there a way to override the range values for enums and struct elements?

Best Answer

Hello,
Polyspace is not confused but the actual type of an enum (and its signedness) is implementation-dependent.
See this link for a reference to the C standard on this topic.
Some C coding standards like MISRA-C:2012 highlight this problem, with the rule 6.1 "Bit-fields shall only be declared with an appropriate type".
Now, you can have unsigned bitfields by choosing a gnu compiler in your Polyspace project.
But a more portable solution is not to rely on the representation of enums with bitfields.
For example, you could use constants instead:
 typedef unsigned int AnswerType;
 const AnswerType YES = 0u;
 const AnswerType NO  = 1u;
Regards,
Alexandre
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