27. Extract Bit Field from 16-bit Register

#include <stdio.h>
#include <stdint.h>

uint8_t extract_field(uint16_t reg) {
    
    uint16_t mask = ((1 << ((8 -  4) + 1 )) - 1) << 4;

    reg &= mask;

    return reg >> 4;
}

int main() {
    uint16_t reg;
    scanf("%hx", &reg);
    printf("%u", extract_field(reg));
    return 0;
}