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;


int validate_register(ControlRegister *ctrl) {
    int res = 0;
    if(
        ctrl->bits.enable == 1 && \
        ctrl->bits.priority <= 2 && \
        ctrl->bits.reserved == 0
    )
    res = 1;
    return res;
}

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

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

    return 0;
}

Solving Approach