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) {
    
    return (ctrl->bits.enable)          // enable must be 1
         &&(ctrl->bits.priority<=2)     // pririty less than or equal 2
         &&(ctrl->bits.reserved==0);    // reserved must be 0
}

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

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

    return 0;
}