77. Validate Configuration Register Layout

#include <stdio.h>

typedef struct {
    unsigned short reg;
} ConfigRegister;

int validate_config(ConfigRegister *cfg) {
    if (!cfg) return -1;

    if (((cfg->reg & 1) == 0) || 
        (((cfg->reg >> 2) & 0x3) == 0x3) || 
        (((cfg->reg >> 4) != 0)))
    {
        return 0;
    }

    return 1;
}

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

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

    return 0;
}