77. Validate Configuration Register Layout

#include <stdio.h>

typedef struct {
    unsigned short reg;
} ConfigRegister;

int validate_config(ConfigRegister *cfg) {
    unsigned reserved_mask = 0xFFFU;
    unsigned priority_mask = 0x03U;
    unsigned enable_mask = 0x01U;

    unsigned is_reserved = ((cfg->reg >> 4) & reserved_mask) == 0x0;
    if (!is_reserved) return 0;

    unsigned is_valid_priority = ((cfg->reg >> 2) & priority_mask) != priority_mask;
    if (!is_valid_priority) return 0;

    unsigned is_enabled = (cfg->reg & enable_mask) == enable_mask;
    if (!is_enabled) return 0;

    return 1;  
}

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

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

    return 0;
}