How to interpret 4 bytes in reverse as float without memcpy?

Projects Programming
12

Do you have any suggestions on how to design several different packet types without too much redundancy while keeping the order intact?

For example I would like to do something among the lines of:

struct __attribute__((packed)) GenericPacket {
    uint8_t start_seq[2]; // always {0xBE, 0xEF}
    uint8_t body_size;
    uint8_t packet_type;
    uint8_t header_byte;
    uint8_t body[body_size];
    uint8_t end_seq[2]; // always {0xEF, 0xBE}
};

struct __attribute__((packed)) GenericEntityPacket : public GenericPacket {
    // Replace uint8_t body[body_size]; with:
        uint8_t entity_id;
        uint8_t reserved[3];
        uint8_t remaining_body[body_size-4];
};

// Example: BE EF 08 03 00 58 00 00 00 00 00 C0 40 EF BE
struct __attribute__((packed)) FloatEntityPacket : public GenericEntityPacket {
    // Replace `uint8_t remaining_body[body_size-4];` with
        float value;
};

// Example: BE EF 05 03 00 59 00 00 01 EF BE
struct __attribute__((packed)) BoolEntityPacket : public GenericEntityPacket {
    // Replace `uint8_t value[body_size-4];` with
        uint8 unused[3];
        bool value;
};

// Example: BE EF 05 03 00 5C 00 00 00 04 EF BE
struct __attribute__((packed)) Uint8tEntityPacket : public GenericEntityPacket {
    // Replace `uint8_t value[body_size-4];` with
        uint8 unused[3];
        uint8_t value;
};

// Example: BE EF 01 18 01 02 EF BE
struct __attribute__((packed)) ToggleTunerPacket : public GenericPacket {
    // Replace `uint8_t header_byte;` with:    
        uint8_t state;
    // Replace `uint8_t body[body_size];` with
        uint8_t channel;
};

// Example: BE EF 00 1E 02 EF BE
struct __attribute__((packed)) SdRecordPacket : public GenericPacket {
    // Replace `uint8_t header_byte;` with:    
        uint8_t state;
    // Remove `uint8_t body[body_size];`
};

// Example: BE EF 01 1A 01 04 EF BE
struct __attribute__((packed)) SnapshotPacket : public GenericPacket {
    // Replace `uint8_t header_byte;` with:    
        uint8_t action;
    // Replace `uint8_t body[body_size];` with
        uint8_t slot;
};

Edit: Moved to How to elegantly inherit from struct overriding/adding fields