Control Register Using Nested Bitfields

Code

#include <stdio.h>

typedef union {
    unsigned char reg;
    struct {
        unsigned char enable : 1;
        unsigned char mode : 1;
        unsigned char priority : 2;
        unsigned char reserved : 4;
    } bits;
} ControlRegister;

// Write your logic here
int validate_register(ControlRegister *ctrl) {
    int result = 0;
    // validate
    if(ctrl->bits.enable && ctrl->bits.priority <= 2 && ctrl->bits.reserved == 0)
    {
        result = 1;
    }
    
    return result;
}

int main() {
    ControlRegister ctrl;
    scanf("%hhx", &ctrl.reg);

    int result = validate_register(&ctrl);
    printf("%d", result);

    return 0;
}

Solving Approach

/*
Plan:
- check bit 0
- check bit (2 to 3) -> must be <= 2
- check bits (4 -7) -> must be 0

struct inside of union will give me the bit fields

*/