67. Control Register Using Nested Bitfields

#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) {
if(!(ctrl->bits.enable))
    return 0;

if (ctrl->bits.priority > 2)
    return 0;

if (ctrl->bits.reserved != 0)
    return 0;
return 1;
}

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

    int result = validate_register(&ctrl);
    //printf("%d\n",sizeof(ctrl));
    printf("%d", result);

    return 0;
}