Control Register Using Nested Bitfields

Code

#include <stdio.h>
#include <stdint.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) {
    uint8_t validation_sum = 0; 

    if(ctrl->bits.enable){
        validation_sum++;
    }

    if(ctrl->bits.priority <= 2){
        validation_sum++;
    }

    if(!(ctrl->bits.reserved)){
        validation_sum++;
    }

    return (validation_sum == 3) ? 1 : 0;    
}

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

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

    return 0;
}

Solving Approach