77. Validate Configuration Register Layout

#include <stdio.h>

typedef struct {
    unsigned short reg;
} ConfigRegister;

int select_bits(int data, int start, int end)
{
    int mask = (1 << (end - start + 1)) - 1;
    return (data >> start) & mask;
}

int validate_config(ConfigRegister *cfg) {
    return select_bits(cfg->reg, 0, 0) == 1 &&
        (select_bits(cfg->reg, 2, 3) != 0b11) &&
        select_bits(cfg->reg, 4, 15) == 0;
}

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

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

    return 0;
}