77. Validate Configuration Register Layout

#include <stdio.h>

typedef struct {
    unsigned short reg;
} ConfigRegister;

int validate_config(ConfigRegister *cfg) {
    if ((cfg->reg & 0x0001) == 0) {
        // enable bit should be 1
        return 0;
    }
    if (((cfg->reg >> 2) & 0x0003) == 3) {
        // '11' is invalid for priority
        return 0;
    }
    if ((cfg->reg & 0xFFF0) != 0) {
        // no 1's should be in reserved
        return 0;
    }
    return 1;
}

int main() {
    ConfigRegister cfg;
    scanf("%hx", &cfg.reg);

    int result = validate_config(&cfg);
    printf("%d", result);

    return 0;
}